food engineering aspects of baking sweet goods

Food Engineering Aspectsof Baking Sweet Goods

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Copyright 2008 by Taylor and Francis Group, LLC

Contemporary Food Engineering

Series Editor

Professor Da-Wen Sun, DirectorFood Refrigeration & Computerized Food Technology

National University of Ireland, Dublin(University College Dublin)

Dublin, Irelandhttp://www.ucd.ie/sun/

Food Engineering Aspects of Baking Sweet Goods, edited by Servet Gülüm Sumnu and Serpil Sahin (2008)

Computational Fluid Dynamics in Food Processing, edited by Da-Wen Sun (2007)

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www.ucd.ie

Food Engineering Aspectsof Baking Sweet Goods

Edited by

Servet Gülüm SumnuSerpil Sahin

CRC Press is an imprint of theTaylor & Francis Group, an informa business

Boca Raton London New York

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CRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487‑2742

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Library of Congress Cataloging‑in‑Publication Data

Food engineering aspects of baking sweet goods / editors, Servet Gulum Sumnu, Serpil Sahin.

p. cm. ‑‑ (Contemporary food engineering)Includes bibliographical references and index.ISBN 978‑1‑4200‑5274‑9 (hardback : alk. paper)1. Baked products‑‑Analysis. 2. Food‑‑Analysis. I. Sumnu, Servit Gulum. II.

Sahin, Serpil. III. Title. IV. Series.

TP431.F66 2007664’.752‑‑dc22 2007049013

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To

Erin Bora, Melisa Defne, and Devin Kerem Dindoruk

and

Tuğçe and Gökçe Özkan and Kaan Demirezen

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ii

ContentsSeries Editor’s Preface ..............................................................................................ixPreface ......................................................................................................................xiAbout the Series Editor .......................................................................................... xiiiAbout the Editors .....................................................................................................xvContributors ...........................................................................................................xvii

Chapter 1 Soft Wheat Quality ..............................................................................1

Edmund J. Tanhehco, Perry K.W. Ng

Chapter 2 Functions of Ingredients in the Baking of Sweet Goods ................... 31

Dasappa Indrani, Gandham Venkateswara Rao

Chapter 3 Chemical Reactions in the Processing of Soft Wheat Products ........ 49

Hamit Köksel, Vural Gökmen

Chapter 4 Cake Emulsions .................................................................................. 81

Sarabjit S. Sahi

Chapter 5 Cake Batter Rheology ........................................................................99

Serpil Sahin

Chapter 6 Cookie Dough Rheology .................................................................. 121

Meryem Esra Yener

Chapter 7 Technology of Cake Production ....................................................... 149

Suzan Tireki

Chapter 8 Technology of Cookie Production .................................................... 159

Suzan Tireki

Chapter 9 Heat and Mass Transfer during Baking of Sweet Goods ................. 173

Weibiao Zhou, Nantawan Therdthai

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iii FoodEngineeringAspectsofBakingSweetGoods

Chapter 10 Physical and Thermal Properties of Sweet Goods ........................... 191

Shyam S. Sablani

Chapter 11 Alternative Baking Technologies ..................................................... 215

Dilek Kocer, Mukund V. Karwe, Servet Gülüm Sumnu

Chapter 12 Low-Sugar and Low-Fat Sweet Goods .............................................245

Manuel Gómez

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ix

SeriesEditor’sPreface

Contemporary Food engineering

Food engineering is the multidisciplinary field of applied physical sciences combined with the knowledge of product properties. Food engineers provide the technological knowledge transfer essential to the cost-effective production and commercialization of food products and services. In particular, food engineers develop and design pro-cesses and equipment in order to convert raw agricultural materials and ingredi-ents into safe, convenient, and nutritious consumer food products. However, food engineering topics are continuously undergoing changes to meet diverse consumer demands, and the subject is being rapidly developed to reflect market needs.

In the development of food engineering, one of the many challenges is to employ modern tools and knowledge, such as computational materials science and nano-technology, to develop new products and processes. Simultaneously, improving food quality, safety, and security remain critical issues in food engineering study. New packaging materials and techniques are being developed to provide more protection to foods, and novel preservation technologies are emerging to enhance food security and defense. Additionally, process control and automation regularly appear among the top priorities identified in food engineering. Advanced monitoring and control systems are developed to facilitate automation and flexible food manufacturing. Fur-thermore, energy saving and minimization of environmental problems continue to be an important food engineering issue and significant progress is being made in waste management, efficient utilization of energy, and reduction of effluents and emissions in food production.

Consisting of edited books, the Contemporary Food Engineering book series attempts to address some of the recent developments in food engineering. Advances in classical unit operations in engineering applied to food manufacturing are covered as well as such topics as progress in the transport and storage of liquid and solid foods; heating, chilling, and freezing of foods; mass transfer in foods; chemical and biochemical aspects of food engineering and the use of kinetic analysis; dehydration, thermal processing, nonthermal processing, extrusion, liquid food concentration, membrane processes and applications of membranes in food processing; shelf-life, electronic indicators in inventory management, and sustainable technologies in food processing; and packaging, cleaning, and sanitation. The books aim at professional food scientists, academics researching food engineering problems, and graduate-level students.

The editors of the books are leading engineers and scientists from many parts of the world. All the editors were asked to present their books in a manner that will address the market need and pinpoint the cutting-edge technologies in food engineer-ing. Furthermore, all contributions are written by internationally renowned experts who have both academic and professional credentials. All authors have attempted to

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x FoodEngineeringAspectsofBakingSweetGoods

provide critical, comprehensive, and readily accessible information on the art and science of a relevant topic in each chapter, with reference lists to be used by readers for further information. Therefore, each book can serve as an essential reference source to students and researchers in universities and research institutions.

Da-Wen Sun, Series Editor

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xi

PrefaceBaking is a complex food process that involves simultaneous heat and mass transfer. Understanding the baking process is necessary for process and product develop-ment. The books dealing with this topic mainly concentrate on different product formulations and functions of ingredients in cookies, cakes, and so forth. To date, baking has been a field of trial and error. In this book, we chose to look at the topic of baking from a different perspective. We aimed to combine engineering and science aspects of baking, as this is lacking in baking books.

Rheological and emulsion properties of dough and batter, physical properties of sweet goods, and heat and mass transfer during baking are important in under-standing the baking process. For this reason, in this book we include chapters on the rheology of cake batter and cookie dough, physical and thermal properties of sweet goods, cake emulsions, and heat and mass transfer during baking. In addition, information is presented on the food science aspects of soft wheat products, includ-ing quality of soft wheat, functions of ingredients in the baking of sweet goods, and chemical reactions during processing. Moreover, information on cake and cookie technology is provided. The principles of recent technologies for baking soft wheat products, such as jet impingement, microwave and hybrid ovens, and recent studies in this area are also summarized. Presented in the last chapter of this book is a sum-mary of the nutritional issues regarding the consumption of fats and sugars and gen-eral strategies of substituting fats and sugars in baked products, because the recent trend among consumers is to consume low-calorie products.

Various experts in different fields from different countries contributed to this book. The editors believe that this book will be helpful for undergraduate or gradu-ate students who are working in the field of baking, food science, and food engineer-ing, and also people from the food industry.

Servet Gülüm SumnuSerpil Sahin

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xiii

AbouttheSeriesEditorBorn in Southern China, Professor Da-Wen Sun is internationally recognized for his leadership in food engineering research and education. His main research activities include cooling, drying, and refrigeration processes and systems, quality and safety of food products, bioprocess simulation and optimization, and computer vision tech-nology. Especially, his innovative studies on vacuum cooling of cooked meats, pizza quality inspection by computer vision, and edible films for shelf-life extension of fruits and vegetables have been widely reported in national and international media. Results of his work have been published in over 150 peer-reviewed journal papers and more than 200 conference papers.

He received first class B.Sc. Honors and M.Sc. in mechanical engineering, and a Ph.D. in chemical engineering in China before working in various universities in Europe. He became the first Chinese national to be permanently employed in an Irish University when he was appointed college lecturer at National University of Ireland, Dublin (University College Dublin), in 1995, and was then rapidly promoted to senior lecturer, associate professor, and full professor. Sun is now professor and director of the Food Refrigeration and Computerized Food Technology Research Group in University College Dublin.

As a leading educator in food engineering, Sun has contributed significantly to the field of food engineering. He has trained many Ph.D. students, who have made their own contributions to the industry and academia. He has also, on a regular basis, given lectures on advances in food engineering in academic institutions internation-ally and delivered keynote speeches at international conferences. As a recognized authority in food engineering, he has been conferred adjunct and visiting and consult-ing professorships from ten top universities in China including Zhejiang University, Shanghai Jiaotong University, Harbin Institute of Technology, China Agricultural University, South China University of Technology, and Southern Yangtze University. In recognition of his significant contribution to food engineering worldwide and for his outstanding leadership in the field, the International Commission of Agricultural Engineering (CIGR) awarded him the CIGR Merit Award in 2000 and again in 2006 and the Institution of Mechanical Engineers (IMechE) based in the United Kingdom named him Food Engineer of the Year 2004.

He is a Fellow of the Institution of Agricultural Engineers. He has also received numerous awards for teaching and research excellence, including the President’s Research Fellowship, and twice received the President’s Research Award of Univer-sity College Dublin. He is a member of the CIGR Executive Board and Honorary Vice-President of CIGR, editor-in-chief of Food and Bioprocess Technology—An International Journal (Springer), series editor of the “Contemporary Food Engi-neering” book series (CRC Press/Taylor & Francis), former editor of Journal of Food Engineering (Elsevier), and editorial board member for Journal of Food Pro-cess Engineering (Blackwell), Sensing and Instrumentation for Food Quality and Safety (Springer), and Czech Journal of Food Sciences. He is also a chartered engi-neer registered in the UK Engineering Council.

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x

AbouttheEditorsServet Gülüm Sumnu is an associate professor in the Department of Food Engi-neering, Middle East Technical University, Ankara, Turkey. She has authored or coauthored 55 journal articles and book chapters. She is one of the authors of Physi-cal Properties of Foods (2006, Springer). She received BS (1991), MS (1994), and PhD (1997) degrees from the Department of Food Engineering, Middle East Tech-nical University. Sumnu was a visiting scholar in the Department of Food Science and Technology at the Ohio State University for one year (1996). She is working on microwave food processes, especially microwave baking and frying. Her research also focuses on physicochemical properties of hydrocolloids and the determination of physical properties of foods.

Serpil Sahin is an associate professor in the Department of Food Engineering, Mid-dle East Technical University, Ankara, Turkey. She has authored or coauthored about 40 journal articles and book chapters. She is one of the authors of Physical Proper-ties of Foods (2006, Springer). She received BS (1989), MS (1992), and PhD (1997) degrees from the Department of Food Engineering, Middle East Technical Univer-sity. Sahin was a visiting scholar in the Department of Food Science and Technology at the Ohio State University for one year (1996). She is working on food processes, especially frying, baking, separation processes, and applications of the microwave.

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xii

Contributors

Vural GökmenDepartment of Food EngineeringHacettepe UniversityAnkara, Turkey

Manuel GómezE.T.S. Ingenierías Agrarias. AvdaMadrid, Spain

Dasappa IndraniFlour Milling, Baking, and

Confectionery TechnologyCentral Food Technological Research

InstituteMysore, India

Mukund V. KarweDepartment of Food ScienceRutgers, The State University of New

JerseyNew Brunswick, New Jersey

Dilek KocerNational Food Starch InnovationBridgewater, New Jersey

Hamit KökselDepartment of Food EngineeringHacettepe UniversityAnkara, Turkey

Perry K.W. NgDepartment of Food Science and

Human NutritionMichigan State UniversityEast Lansing, Michigan

Gandham Venkateswara RaoFlour Milling, Baking, and

Confectionery TechnologyCentral Food Technological Research

InstituteMysore, India

Shyam S. SablaniDepartment of Biological Systems

EngineeringWashington State UniversityPullman, Washington

Sarabjit S. SahiCereals Processing and Bakery ScienceCampden and Chorleywood Food

Research AssociationGloucestershire, United Kingdom

Serpil SahinDepartment of Food EngineeringMiddle East Technical UniversityAnkara, Turkey

Servet Gulum SumnuDepartment of Food EngineeringMiddle East Technical UniversityAnkara, Turkey

Edmund J. TanhehcoMennel Milling CompanyFostoria, Ohio

Nantawan TherdthaiDepartment of Product Development,

Faculty of Agro-IndustryKasetsart UniversityBangkok, Thailand

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xiii FoodEngineeringAspectsofBakingSweetGoods

Suzan TirekiETI Group of CompaniesEskisehir, Turkey

Meryem Esra YenerDepartment of Food EngineeringMiddle East Technical UniversityAnkara, Turkey

Weibiao ZhouFood Science and Technology ProgramNational University of SingaporeSingapore

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1 Soft Wheat QualityEdmund J. Tanhehco, Perry K.W. Ng

Contents

1.1 Introduction.....................................................................................................21.2 WheatProduction,Classification,andUsage.................................................2

1.2.1 Texture.................................................................................................31.2.2 Color.....................................................................................................31.2.3 Growth.................................................................................................3

1.3 FlourMilling...................................................................................................31.4 MajorConstituentsofSoftWheatFlour.........................................................5

1.4.1 Proteins................................................................................................51.4.2 Starch...................................................................................................51.4.3 Pentosans..............................................................................................61.4.4 Lipids...................................................................................................7

1.5 QualityEvaluationofWheatGrainandFlour................................................71.5.1 WheatGrain.........................................................................................8

1.5.1.1 TestWeight.............................................................................81.5.1.2 ExperimentalMilling.............................................................81.5.1.3 BreakFlourYield...................................................................81.5.1.4 KernelTexture........................................................................8

1.5.2 WheatFlour.........................................................................................91.5.2.1 Moisture.................................................................................91.5.2.2 Ash....................................................................................... 101.5.2.3 Protein.................................................................................. 101.5.2.4 SproutDamage..................................................................... 101.5.2.5 DamagedStarch................................................................... 111.5.2.6 PolyphenolOxidase.............................................................. 111.5.2.7 AlkalineWaterRetentionCapacityofFlour....................... 111.5.2.8 SolventRetentionCapacityofFlour.................................... 11

1.5.3 DoughRheology................................................................................ 121.5.3.1 Alveograph........................................................................... 131.5.3.2 MixographandFarinograph................................................. 14

1.5.4 ProductsRequiringWeakerProteins................................................. 141.5.4.1 Cookies................................................................................. 141.5.4.2 High-RatioCakes................................................................. 16

1.5.5 ProductsRequiringStrongerProteins............................................... 161.5.5.1 Crackers................................................................................ 161.5.5.2 Noodles................................................................................. 16

1.6 EffectsofFlourComponentsonCookies..................................................... 171.6.1 Proteins.............................................................................................. 17

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Food Engineering Aspects of Baking Sweet Goods

1.6.2 Starch................................................................................................. 181.6.3 Pentosans............................................................................................ 191.6.4 Lipids................................................................................................. 19

1.7 EffectsofFlourComponentsonCakes........................................................201.7.1 FlourParticleSize..............................................................................201.7.2 Proteins..............................................................................................201.7.3 Lipids................................................................................................. 21

1.8 FlourChlorination......................................................................................... 211.8.1 Starch.................................................................................................221.8.2 Lipids.................................................................................................221.8.3 Proteins..............................................................................................231.8.4 AlternativestoChlorination..............................................................24

1.9 Conclusion.....................................................................................................24References................................................................................................................24

. IntroduCtIon

Thecategoryofsweetgoodsmadefromwheatflourencompassesawidevarietyofproductswithdifferentappearances,textures,flavors,nutritionalvalues,andshelflives.Theseincludedifferenttypesofcakes,cookies,doughnuts,pastries,andmanymoreitems.Thequalityofthesegoodsbeginswiththatofthesoftwheatflourusedtoproduce them.Flourquality is, in turn,affectedby thewheatgenotype,grow-ing environment, and processing. The genotype and growing environment deter-minetheamountandcharacteristicsofthewheatcomponents,includingproteins,carbohydrates, and lipids. To produce high-quality flour, wheat must be properlymilled;postmillingprocessingsuchaschlorinationisalsosometimesutilizedforitsbenefits.Qualitytestingassuresthataflourmeetsanynecessarystandardsandgivesvaluable information to thoseseekingto improve it.These tests include thedeterminationofproximatecompositionalongwithvariouschemical,rheological,andbakingtests.Thefollowingsectionsofthischapterdescribethemillingofsoftwheatintoflour,compositionofflour,qualitytesting,andhowflourpropertiesrelatetothequalityofproductssuchascookiesandcakes.

. WheatProduCtIon,ClassIfICatIon,andusage

Wheat isoneof themajorcropsgrown in theworld,withover620millionmet-rictons(MMT)producedworldwidein2005(USDAForeignAgricultureService2007).U.S.andCanadianwheatproductionaccountedforover57and26MMT,respectively.Commonwheat,Triticumaestivum,isusedforawiderangeofprod-uctsincludingbreads,cakes,cookies,crackers,noodles,breakfastcereals,andmuchmore.Whendescribingwheatvarieties,classificationcanbebasedontexture,color,andgrowthhabit.

1.2.1 TexTure

Wheatiscategorizedashardorsoftbasedonkerneltexture,oneofthemajordeter-minantsofenduse.Comparedtowheatwithasoftertexture,hardwheatrequires

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Soft Wheat Quality

moreenergytobemilledintoflourandproducesacoarserflour,andalsoonewithmore starch damage. Conversely, wheat kernels with softer texture produce finerflourwithlessstarchdamage,bothimportantattributesofhigh-qualitysoftwheatflour.Themajority ofwheat grownworldwide is hard. In theUnitedStates, softwheataccountsforabout25%ofwheatproduction.

1.2.2 Color

Wheatcanalsobeclassifiedasredorwhitedependingonthecolorofthebrancover-ingthewheatkernel.Themajordifferencebetweenthetwo,otherthanappearance,isthegreatersusceptibilityofwhitewheattosproutingunderfavorable(moistandwarm)conditions.Thismakes theuseofwhitewheatundesirableforsomefood-processingapplicationssuchasthickening.However,thereareadvantagestowhitewheat,suchasthebranbeinglessbitterinflavor.Millingyields(orextractionrates)canalsobehigherinsomecasesbecausethebranofwhitewheatdoesnotdarkenflourasmuchasredwheatbran(LinandVocke2004).

1.2.3 GrowTh

Wheatplantedinthespringandharvestedinlatesummerinthesameyearisreferredtoasspringwheat.Winterwheatisusuallyplantedinlatesummerorearlyfallandharvested the followingsummer.Soft redwinterwheataccounts for themajorityof soft wheat planted in the United States. Major soft wheat producing areas liearoundtheMississippiRiver,Ohio,andsomeareasontheeastcoast(USDAEco-nomicResearchService2006).StatesthatgrowsoftwhitewheatincludethoseinthePacificNorthwest(Washington,Oregon,andIdaho),alongwithMichiganandNewYork.TheprovincesofOntarioandAlberta,Canada,accountformuchoftheCanadiansoftwheatproduction.

Hardwheatsaregenerallybredtohavehigherproteincontentthansoftwheats,althoughproteincontentandhardnessarenotnecessarilylinked.Thisreflectsthedifferentend-userequirementsofhard(>11%protein)andsoftwheatflours(8to10%protein).Themainuseofhardwheatfloursisinbread,wherestrongandhighlevelsofproteinareneeded.Softwheatfloursontheotherhandareusedinproductswhereweakerprotein (i.e.,weakerdough strengthandweakerviscoelasticproperties) isdesired,includingproductssuchascakesandcookies.However,softwheatfloursarealsousedforawiderangeofgoods,somerequiringhigherlevelsofproteins,althoughnotnecessarily“strong”proteins.Crackersandnoodlesfallintothiscategory.

. flourMIllIng

Themajorcomponentsofthewheatkernelaretheoutercoveringofbran,theembryoorgerm,andtheendosperm.Thegoalofflourmillingistoseparatethesethreeascleanlyaspossible,alongwithreducingtheendospermintoflourparticles.Higherextractionratesofflour,whileeconomicallydesirable,mayresultinflourwithexces-sivebrancontamination(andtherebyhigherashcontent)aswellasincreasedstarchdamage.Therefore,aproperbalanceneedstobeachieved,dependingonthedesiredenduseoftheflour.

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Aftercleaningthewheatofanydebris,thefirststepinmillingistheadditionofwater,referredtoastempering.Thepurposeoftemperingistotoughenthebran,keepingitinlargerflakes,therebyreducingtheamountofsmallbranparticleslatercontaminating the flour. An additional benefit of tempering is that it softens theendosperm, further reducingbreakageof thebranwhen it is crushed against theendospermduringmilling.Theamountofwateraddedintemperingvariesdepend-ingonthehardnessofthewheatandtheflourmillmachinerybeingused.Softwheatiscommonlytemperedtoaround14to15%moisture;hardwheatrequireshigherlevels.Thetimeneededfortemperingcanrangefromafewhoursupto24h,againdependingonthewheat.DetailedinformationonwheattemperingandpreparationforexperimentalmillingcanbefoundintheAmericanAssociationofCerealChem-istsInternational(AACCI)Method26-10A(AACCInternational2000).

Theproductionofflourisachievedthroughrollermillingwhichinvolvessetsoftwosteelrollsspinninginoppositedirections,betweenwhichthewheatfallstobeground.Theflourmilliscomposedoftwomainsystems:thebreakandthereduction.Thepurposeof thebreaksystemis to ripopen thewheatkernelandseparate the endosperm from the bran as cleanly as possible. This is achievedwithcorrugatedrollsturningwithadifferentialinspeed.Theslowerrollservestoholdthekernelwhilethefasterrollbreaksitopen.Multiplepassesthroughdif-ferentsetsofbreakrollswithdifferentgapsandcorrugationsareusedtoachieveagradualseparationofthebranandendosperm,whilekeepingthebranasintactaspossible.Inadditiontoseparatingthebranandendosperm,someflourisalsoproducedaftereachpassthroughthebreakrollsandissiftedout.Wheatwithasofterkerneltexturefracturesmoreeasilyandproducesmoreflourinthebreaksystemthandoeswheatwithahardertexture(Finney1989).Flourobtainedinthebreaksystemiscalled“breakflour”andhasasmallerparticlesizethantheflourproducedlateronduringmillinginthereductionsystem(i.e.,reductionflour).Theremainingendospermfreedbythebreakrollsrequiresfurthermillingandgoesontothereductionsystem.

Thereductionsystemissimilartothebreaksystemwiththemaindifferencebeingthatthereductionrollsaresmooth.Multiplepassesthroughdifferentreduc-tionrollswithsievinginbetweeneachpassareusedtograduallyreducetheendo-spermtoflourofthedesiredparticlesize.Thisgradualreductionisdonetocontrolthelevelofstarchdamage.Adjustingthepressurebetweentherollsandchangingtheleveloftemperingcanalsohelptocontroltheamountofstarchdamageinthemilledflour.

Furtherdownstreaminthemillingprocess,ashcontentishigherduetoincreasesinfinebrancontamination,andstarchdamageishigherduetothenarrowerreduc-tion roll gaps.Therefore, thedifferent break and reductionflour streamsneed tobe selectively blended together to produce flour with the desired characteristics.Straight-gradefloursareacombinationofalloftheflourstreams.Patentflourscon-sistofhigher-gradestreamswithlessbran(lighterincolor)andconsequentlylessash,andclearflourshavehigherbrancontamination(darkerincolor)andhigherash.Detailedinformationregardingmillingcanbefoundintheliterature(PosnerandHibbs1997).

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Soft Wheat Quality

. MajorConstItuentsofsoftWheatflour

Theconstituentsofwheatflourvaryduetothegenotypeandthegrowingenviron-ment.These, in turn,determine theend-usecharacteristics,withcertainvarietiesofwheatbeingbettersuitedtospecifictypesofproducts.Themostimportantflourconstituentsinrelationtoflourfunctionalityincludetheproteins,starches,pento-sans(thelargestportionofnonstarchpolysaccharides),andlipids.

1.4.1 ProTeins

Osborne(1907)fractionatedwheatproteinsintofourclassesbasedontheirsolubilityindifferentsolvents.Byhisclassification,albuminswereproteinssolubleinwater,andglobulinsweresolubleinsaltsolutions.Prolaminswerefoundtobesolublein70to85%ethanol,andglutelinsweresolubleindiluteacid.Overthedecades,fur-therworkwasdonetofractionatetheproteins,asthereissomeoverlapbetweenthedifferentclassesandbecausestillfurtherfractionationcanbedonewithdifferentsolvents(ChenandBushuk1970;Kreisetal.1985).

Wheatproteinshavetheuniqueabilitytoformaviscoelasticnetworkthatallowsfortheproductionofproductssuchasbread.Theproteinsmainlyresponsiblefortheviscoelasticpropertiesofflourarethegliadins(prolamins)andglutenins(glutelins).Gluteninsarelargepolymericproteinsheldtogetherbydisulfidebonds.Thesepro-teinsgivedoughstrengthandelasticity.Gliadinsaresmallermonomericproteinsthatareresponsiblefordoughextensibility.Togethertheseproteinsformtheglutenpro-teins.Boththequantity(amount)andquality(type)ofproteinareimportanttoflourcharacteristics.Thestrongglutenproteinsfoundinhardwheatflourareabletoformanetworkwithgoodgas-retainingpropertiesvitalforyeast-leavenedproducts.

Softwheatfloursaretypicallylowinproteincontent(8to10%)andtheproteinsareweakinstrength,characteristicsbettersuitedtomakingmoretenderproductssuchascakesandcookies.Most researchhasbeenfocusedonunderstanding themoreobvious roleofproteins inhardwheatproducts,with less focuson the roleofproteinsinsoftwheatproducts.However,studieshaveshownthatinadditiontoquantity,proteincompositionisimportantinsoftwheatproducts,makingitsstudynecessary(FinneyandBains1999;Houetal.1996a,1996b;Huebneretal.1999;Souzaetal.1994).

1.4.2 sTarCh

Ingeneral,wheatflourcontainsover70%starch (SollarsandRubenthaler1971)thatiscomposedofapproximately25%amyloseand75%amylopectin.Amyloseisaprimarilystraight-chainpolymerofα-1,4-linkedD-glucopyranosemolecules.Amylopectin isabranchedpolymerofα-1,4-linkedglucoseconnectedbyα-1,6-linkedbranchpoints.Amyloseandamylopectinareorganizedinstarchgranulesrangingfrom1to45µmindiameter.Wheatstarchgranulescomeintwoforms:ovaltypeAgranulesabout35µmindiameter,androundtypeBgranulesapproxi-mately3µmindiameter(Alexander1995).Oneofthemostimportantpropertiesofstarchisitsabilitytoswellandabsorbwaterwhenitisheatedinexcesswater.Asstarchgranulesswell,theycauseanincreaseintheviscosityofthestarch–water

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slurry,untileventuallythegranulesbreakdown,releasingprimarilyamylose,fol-lowed by amylopectin. Upon cooling, the starch molecules, especially amylose,canreassociate,formingagel.Theprocessesofgranuleswellingandbreakdownarereferredtoasgelatinizationandpasting,respectively,andcanbevisualizedinwheatflourbymeasuringtheviscosityofaflour–waterslurryasitisheatedandcooled(Figure1.1).Thesepropertiesofstarchareimportantinmanyaspectsrelat-ingtoflourqualitybecausetheyinfluencetheinteractionsofstarchandwaterinafoodsystem.

Starchgranulescanbephysicallydamagedduringflourmilling,increasingtheirwater-holdingabilityandsusceptibilitytoattackfromtheenzymeα-amylase.GreerandSteward(1959)foundthat2gofwaterwasabsorbedbyeachgramofdamagedstarch,comparedtoonly0.44gofwaterabsorbedbyeachgramofnativestarch.Softwheatflour, ingeneral, is lower indamaged starch content thanhardwheatflour,duetothesofterkerneltextureandhigherbreakflouryield.Inbreadflour,acontrolledamountofdamagedstarchisneededbecausetheenzymaticbreakdownof starch provides some food for the yeast. However, in soft wheat products, theincreasedwaterabsorptionassociatedwithincreasedlevelsofdamagedstarchcanbedetrimentaltoproductquality.

1.4.3 PenTosans

Pentosansarecarbohydratesofinterestduetotheirabilitytoabsorbtentimestheirownweightinwater(D’AppoloniaandKim1976;Kulp1968).Theyarefoundinthe

500

400

300

200

100

0

Temperature

Viscosity

Time (minutes)

Tem

pera

ture

(˚C

)100

90

80

70

60

50

40

30

200 5 10 15 20

Visc

osity

(RV

U)

fIgure. RapidViscoAnalyzerpastingcurveof3.5gofsoftwheatflourin25mlofwater.(RVU:viscosityinRapidViscounits.)

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Soft Wheat Quality

cellwallsofwheatendospermandbranandarecomposedmainlyofarabinoxylan,apolymerwithaβ-(1-4)-linkedD-xylopyranosebackboneandbranchesofL-arabino-furanoseresidues(Cole1967;Gruppenetal.1992;Perlin1951a,1951b;Wangetal.2006).Pentosansexistasbothwater-insolubleandwater-solubleforms,dependingonthedegreeofbranchingofthearabinosesidechains.Ahigherdegreeofarabi-nosesubstitutionisassociatedwithhigherwatersolubility(Hoseney1984;MedcalfandGilles1968;Wangetal.2006).Wangetal.(2006)measuredthetotalpentosancontentinsixvarietiesofhardspringwheatandfoundittorangefrom5.45to7.32%ofthewholegrainandfrom1.88to2.04%ofthestraight-gradefloursproducedfromthisgrain.Theratioofwater-solubletowater-insolublepentosansinthisflourwas0.36:0.37.Pentosancontentwasalsofoundtobehigherinthelower-gradestreamsofflour,animportantfacttoconsiderwhenblendingmillingstreams.Finnieetal.(2006)specificallymeasured thearabinoxylancontent insoftwhitewinterwheatflourandfoundvariationamongcultivarstobegreatestinthewater-solublefraction,rangingfrom3.23to5.74mgxyloseequivalentspergramsample.Water-insolublearabinoxylanrangedfromabout7to10andtotalarabinoxylanfromabout11to13.5mgxyloseequivalentspergramsampleofsoftwhitewinterwheatflour.

1.4.4 liPids

Flourlipidsareimportantforqualityattributesofsoftwheatproductssuchascookiespreadandcakevolume.Wholegrainwheatcontainsapproximately2 to4%andtheendospermabout1 to2%crudefat (Morrison1978a). Inflour, lipidsexistaseithernonstarchlipidsorstarchlipidsthatareheldinamylose-inclusioncomplexesin starch granules (Acker and Becker 1971). Starch lipids are deemed to be lessfunctionally important than nonstarch lipids due to their protected environment.Supporting evidence of this is that chlorination of flour (see Section 1.8) affectsnonstarchlipidsbutnotstarchlipids(Morrison1978b).Thenonstarchlipidscanbecharacterizedastwotypes:freelipidsextractablewithpetroleumordiethylether,andboundlipidsextractablewithcoldpolarsolventmixtures(Morrison1978a).Thefreelipidscanbefurtherfractionatedintononpolarlipids(triglycerides,diglycer-ides,monoglycerides,fattyacids,sterols,andhydrocarbons)andpolarlipids(gly-colipids and phospholipids). The bound polar lipids consist of phospholipids andglycolipids(Pomeranz1988).

. QualItyevaluatIonofWheatgraInandflour

Characterizationofwheatgrainandwheatflourisnecessaryforbothcommercialandresearchpurposes.Potentialbuyersneedtoknowifwhattheywillbegettingwillmeettheirneeds,andresearchersusethesemethodstobetterunderstandhowflouraffectsend-usequality.

Qualitytestsonwheatgrainincludedeterminingthetestweight,millingyield,andkernelhardness.Flouristypicallytestedforproximatecompositionalongwithvariouschemical,rheological,andbakingtests.

52748.indb 7 2/6/08 2:24:34 PM



1.5.1 wheaTGrain

... testWeight

Testweight isameasureof theweightofgrainperunitvolumeinkilogramsperhectoliter(kg/hl)orpoundsperbushel(lb/bu)(AACCIMethod55-10).Highertestweightsaregenerallycorrelatedwithgreatermillingflouryield;lowertestweightsresultingfromshriveledandlesssoundkernelsresultinlowerflouryields(Gainesetal.1997).

... experimentalMilling

Flouryieldisdependentontheamountofendosperminthekernelandhowwellit can be separated from the bran. As mentioned previously, flour yield must bebalancedwithflourqualitycharacteristicssuchasstarchdamageandashcontent.Themillingcharacteristicsofsmallquantitiesofwheat(<1kg)canbeevaluatedbylaboratoryscaleexperimentalmilling.AACCIMethods26-30A,26-31,and26-32describeprocedures formilling softwheatflourwith aBühlerMLU-202 experi-mentalmill(BühlerInc.,Uzwil,Switzerland).Thismillproducesthreebreakandthreereductionflourstreams.TheBrabenderQuadrumatJr.experimentalmill(C.W.BrabenderInstruments,Inc.,SouthHackensack,NJ)issuitedforsmallersamplesthantheBühlerMLU-202andproducesflourandbranafterpassingwheatthroughafixed setof threebreaks (AACCIMethod26-50).TheUSDA-ARSSoftWheatQualityLaboratoryinWooster,OH,hasalsodevelopedandmodifiedexperimentalmillingmethods tobetter evaluate themillingqualityof softwheat (Finney andAndrews1986;Gaines et al. 2000;Yamazaki andAndrews1982). In addition tovaluableinformationregardingmillingquality,theflourproducedbythesemillsisimportantforuseinflourqualityevaluation.

... Breakflouryield

Thebreakflouryield,expressedasapercent, is theweightof theflourproducedbythebreakrollsrelativetotheweightofallproductsobtainedfromthecombinedbreakand reduction rolls (all streamsofflour,bran, andgerm). It is anexcellentindicatorofwheathardness,becausesofterwheatproducesmorebreakflour.Forsoftwheatproducts,higherbreakflouryieldsareparticularlyimportantbecauseofthedesireforflourwithfinerparticlesizeandlowerstarchdamage.TypicalbreakflouryieldsfromaBühlerexperimentalmillusedintheMichiganStateUniversityWheatQualityTestingProgram(millingsoftwhitewinterwheat)arearound30%ofthetotalproductsrecoveredfrommilling(Figure1.2;Ngetal.2007),withharderwheatsgivingalowerpercentageofbreakflour,typicallylessthan25%.

... Kerneltexture

Inadditiontocomparingbreakflouryieldsfrommilling,standardizedmethodsexisttomeasurekernelhardness.Particlesizeindex(AACCIMethod55-30)ismeasuredbyusingastandardizedgrindertomillgrainintomealfollowedbyweighingwhatmealpassesthroughaU.S.No.75sieve.Asofterwheatpassesmoreofthemeal

52748.indb 8 2/6/08 2:24:34 PM


Soft Wheat Quality

throughthesieve.Anear-infrared(NIR)instrumentcanalsobecalibratedtomea-surehardnessofasampleofgroundwheat(AACCIMethod39-70A).

AmoreconvenientandincreasinglyutilizedwayofmeasuringkernelhardnessiswiththeSingleKernelCharacterizationSystem(SKCS;PertenInstruments,Huddinge,Sweden).Hardnessismeasuredbyassigningahardnessindexvaluetothesamplebasedontheforceneededtocrushtheindividualkernels(AACCIMethod55-31;Martinetal.1993).TherehasbeensomelimitedinformationreportedontheuseoftheSKCSforassessingsoftwheats.Gainesetal.(1996a)reportedarelationshipbetweenSKCShard-nessvaluesandsoftnessequivalent(whichisameasureofbreakflouryieldusedbytheUSDA-ARSSoftWheatQualityLaboratoryinWooster,OH)foragroupofsoftwheatcultivars.However,Hazenetal.(1997)didnotfindasignificantrelationshipbetweenSKCShardnessvaluesandsoftnessequivalentfortheirgroupoftestedsoftwheatcul-tivars.ThiscouldbeduetothefactthattheSKCSwasdevelopedinitiallyforahard-wheat-growingregionandperhapsthesensitivityofthemeasuredvaluesrequiressomeadjustmentforverysoftwheatcultivars.Nevertheless,itappearsthattheSKCScanstillbeusedwithsoftwheatsforevaluationofhardness,inrelativeterms.

1.5.2 wheaTFlour

... Moisture

The moisture content of flour is most easily determined from the difference inweightofasamplebeforeandafterdryinginanairoven(AACCIMethods44-15A

33

32

31

30

29

28

27

26

255 10 15 20 25 30 35 40 45

Hardness Index

Brea

k Fl

our Y

ield

(%)

fIgure. ScatterplotofhardnessindexmeasuredbytheSingleKernelCharacterizationSystemandbreakflouryieldofMichigansoftwhitewinterwheatmilledinaBühlerMLU-202flourmill.Wheatvarietiesweregrownintheyears2001to2005.

52748.indb 9 2/6/08 2:24:35 PM


0 Food Engineering Aspects of Baking Sweet Goods

and44-16).MoisturecontentcanalsobedeterminedwithaproperlycalibratedNIRspectrophotometerorwithmoisture-measuringinstrumentsmadebyvariousmanu-facturers.Resultsofflouranalysisareusuallyadjustedto14%moisturebasisasawayofexpressingresultsonaconstantsolidsbasisbetweensamplesthatmayhavedifferentmoisturecontents.

... ash

Ashormineralcontentofflourisoftenmeasuredasanindicatorofthequalityofmilling.As it ishigher in thebran than theendosperm,ashcontent indicates thedegreeofbrancontaminationinflour.However, itshouldbenotedthat theendo-spermashcontentvariesamongwheatgenotypes;therefore,ashlevelsmaynotcom-pletelycorrelatewiththedegreeofbrancontamination(Greffeuilleetal.2005).Ashcontentisalsoofinterestbecauseitiscorrelatedwithflourcolor(KimandFlores1999),anattributethataffectsmarketabilityofaflour.Flourashcontentsaretypi-callybelow0.5%andcanbedeterminedbyincineratingafloursampleinamufflefurnace,leavingonlytheash(AACCIMethods08-01and08-02).

... Protein

Proteincontentistypicallydeterminedindirectlythroughmeasuringnitrogencon-tentbymethodssuchasKjeldahl(AACCIMethod46-11A)andcombustion(AACCIMethod46-30).Acorrectionfactoraccountingforaminoacidcompositionandnon-proteinnitrogen(×5.7)isthenappliedtocalculatetheproteincontent.CalibrationofaNIRspectrophotometerusingeitherofthepreviouslymentionedmethodscanalsobedonetoprovidearapidwayofdeterminingproteincontentthatdoesnotrequirechemicalsorreagents(AACCIMethod39-11).

... sproutdamage

Sproutdamage,causedbyincreasedamountsofα-amylaseactivity,isaprobleminproductswhereahighhotpasteviscosityofthewheatflourisneeded,asinsoupthickeners.Highlevelsofα-amylasearefoundingrainthathasbeguntogerminatebecauseofexposuretomoisturebeforeharvest.Thisenzyme,whilenecessaryinagerminatingkernel,reducessoftwheatflourqualitybyhydrolyzingtheα-1,4-linkedglucosemoleculesofstarch.

Theα-amylaseactivity ingrainorflourcanbemeasuredcolorimetricallybyincubatingitwithdyedandcross-linkedamylosetablets(AACCIMethod22-05).Duetotheirease,however,methodsthatmeasuretheeffectsofα-amylaseactivityonheatedflour-waterslurriesaremorecommonlyused.TheFallingNumberSystem(PertenInstruments,Huddinge,Sweden)providesarapidmethodofassessingsproutdamagebymeasuringthetimeittakesforastirrertofallthroughaheatedwheatmealandwaterorflourandwatergel.Higherlevelsofα-amylasedecreasethevis-cosityofthegel,causingthestirrertofallfaster.WheatwithaFallingNumbervaluebelow300issuspectedtohavesomesproutdamage(KaldyandRubenthaler1987).

Instrumentsthatrecordviscositywhileheatingandstirringaflour–waterslurryincludetheAmylograph(C.W.BrabenderInstruments,Inc.,SouthHackensack,NJ)

52748.indb 10 2/6/08 2:24:36 PM


Soft Wheat Quality

and the Rapid Visco Analyzer (RVA; Newport Scientific Pty. Ltd., Warriewood,Australia)(AACCIMethods22-10and76-21,respectively).Higherα-amylaseactiv-ityresults inacurvewithlowerpeakviscosity.Theresultingcurvecanalsogiveinformationaboutstarchpastingcharacteristicsnotrelatedtosprouting.NoodlesareanexamplewheretexturehasbeencorrelatedwithAmylographandRVApastingproperties suchas thepasting temperatureandpeakviscosity (Bateyet al.1997;Morrisetal.1997;Odaetal.1980).

... damagedstarch

The level of damaged starch canbemeasuredby incubating aflour samplewithα-amylase,followedbymeasurementofthereducingsugarsorglucosethatarepro-duced (AACCI Methods 76-30A and 76-31). In soft wheat flour, damaged starchtypicallyisbelow3%.Levelsaslowaspossiblearepreferredduetotheincreasedsusceptibilityofdamagedstarchtotheactionofamylasesduringfoodprocessing.

... Polyphenoloxidase

Polyphenoloxidase (PPO), anenzyme that causes the formationof coloredcom-pounds(melanins)fromphenols(Bettge2004;Fuerstetal.2006),ismostlyremovedwiththebranduringmilling.However,somedoesmakeitswayinwiththeflour,especiallyathigherflourextractionrates.Thisenzymeactivityisespeciallydetri-mentaltothequalityofAsiannoodlesduetoitsdarkeninganddiscoloringeffects(Krugeretal.1992,1994).PPOhasalsobeenreportedtodiscolorbatters,piecrusts,andrefrigerateddoughs(Gajderowicz1979).LevelsofPPOinwheatdifferduetoboth genotype and growth environment (Baik 1994a; Park et al. 1997). AACCIMethod22-85wasdevelopedasarapidandsmall-scaletestforPPOactivitythatcanbeusedbybothbreedersand industry (Bettge2004).ThismethodmeasuresPPOactivitybyincubatingwheatorflourwithasubstrate(L-DOPA)andmonitoringthecolorchangespectrophotometrically.

... alkalineWaterretentionCapacityofflour

Alkalinewaterretentioncapacity(AWRC)isatestdevelopedtosimulatethealka-line conditions of the formula for evaluating sugar-snap cookie-making potentialofawheatflour(FinneyandYamazaki1953).Thetestisdefinedastheamountofalkalinewaterheldbytheflouragainstacentrifugalforce.Flourthatbindsalkalinewaterpoorlyisconsideredtobeofgoodquality(AACCIMethod56-10).Yamazaki(1953)foundanegativerelationshipbetweentheamountofalkalinewaterheldbythe flour and cookie diameter. However, the relationship is not as clear for morerecentlydevelopedsoftwheatvarieties(Finney1994)andfordistinguishingamongflourswithinasoftnessorhardnessclass(KittermanandRubenthaler1971).Breed-ers,though,arestillselectingforlowAWRCintheirsoftwheatlines.

... solventretentionCapacityofflour

Morerecently,amethodformeasuringthesolventretentioncapacity(SRC)ofwheatflourwasestablished topredictcommercialflourproperties (AACCIMethod56-

52748.indb 11 2/6/08 2:24:36 PM



11).Thismethodusesfoursolventsindependently—water,50%sucrose,5%sodiumcarbonate,and5%lacticacid—andmeasuresaflour’sabilitytoholdthemaftercen-trifugation.Ingeneral,waterSRCisaffectedbyallflourconstituents,sucroseSRCisassociatedwithpentosancharacteristics,sodiumcarbonateSRCisassociatedwiththelevelofdamagedstarch,andlacticacidSRCisassociatedwithglutenincharac-teristics(Bettgeetal.2002;Gaines2000).

TheuseofdifferentsolventsforSRCallowstheseparationofeffectsofdiffer-entflourcomponents,andthecombinedpatternofthefourSRCprofilesprovidesapracticalflourquality assessment forpredictingbakingperformance (Bettge etal.2002;Guttierietal.2004;SladeandLevine1994).InacollaborativestudybyGaines(2000),lacticacidSRCwasfoundtocorrelatewithMixographnumber(pro-teincontentmultipliedbypeakheightandpeaktime),andsodiumcarbonateSRCwith damaged starch, softness equivalent, AWRC, and sugar-snap cookie spread.SucroseSRCcorrelatedwithdamagedstarch,AWRC,andcookiespread(Table1.1).SRCtestsarecurrentlyusedinanumberofsoftwheatbreedingprograms,includ-ingtheMichiganStateUniversityWheatQualityTestingProgram(Ngetal.2007).VariationsontheSRCmethodsusingsmallerquantitiesofmaterialandwheatmealinsteadofflourhavealsobeendeveloped,allowingforrapidscreeningofearlygen-erationbreederlinesofwheat(Bettgeetal.2002;Guttierietal.2004).

1.5.3 douGhrheoloGy

Withregardtowheatflour,rheologyisthemeasureoftheflowanddeformationofdoughs.Thesedoughpropertiescanaffectproductqualitiessuchasgeometry(e.g., cookie spread or cake volume), texture, and handling during processing.Dough rheological instrumentswereoriginallydesigned forusewithmaterialssuchasbreaddoughs,wherestrengthandelasticityarevalued.Softwheatflourproducts, however, generally require doughs that are weaker. Results obtainedfromtheserheologicalinstrumentsshouldnotbeinterpretedusingthesamecri-

taBle.CorrelationCoefficientsbetweensolventretentionCapacityandvariousflourQualityParameters

Water 0%sucrose

%sodiumCarbonate

%lacticacid

Proteincontent 0.33a 0.39a 0.31a 0.39a

Damagedstarch 0.94a 0.77a 0.95a 0.23

Flouryield 0.51a 0.41a 0.54a –0.06

AWRC 0.97a 0.81a 0.97a 0.33a

SSCdiameter –0.88a –0.76a –0.86a –0.33a

Mixographnumber 0.50a 0.49a 0.43a 0.69a

Notes:AWRC,alkalinewaterretentioncapacity;SSC,sugar-snapcookie.a Significantatthe1%level.

Source:AdaptedfromGaines,C.S.,Cereal Foods World,45,303–306,2000..

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Soft Wheat Quality

teriaasresultsfromhardwheatflours,astherheologicalpropertiesofsoftandhardwheatfloursarenotsimplyopposites(Hoseneyetal.1988).Dough-formingpropertiesoffloursarecommonlyevaluatedusingtheAlveograph,Mixograph,andtheFarinograph.

... alveograph

The Alveograph (Chopin Technologies, Villeneuve-la-Garenne Cedex, France)measures air pressure inside of a dough bubble as it is inflated until it bursts(AACCIMethod54-30A).Thisbiaxialextensionismeanttosimulatethedefor-mationofadoughduringfermentationandovenspringduringbaking.Itallowsforthemeasurementofthemaximumoverpressure(P),whichrelatestotheresis-tanceofdough todeformation,and theaverage lengthof thecurvebaselineatrupture(L),whichisameasureofdoughextensibility.Thedeformationenergy(W)isameasureoftheenergyneededtoinflatethedoughandisderivedfromthe area under the curve. W is related to the flour strength (Faridi and Rasper1987).Bettgeetal.(1989)investigatedtheabilityoftheAlveographtoevaluatesoftwheatvarietiesforcookiesandfoundthattheparameterbestabletopredictcookie diameter was P in combination with the flour protein content. Nemethetal.(1994)foundthatPandP/Lweresignificantlycorrelatedwithsugar-snapcookiespreadandscore.Yamamotoetal. (1996)foundthatAlveographPwasnegativelycorrelatedandLpositivelycorrelatedwithJapanesespongecakevol-ume(Table1.2).

taBle.

CorrelationCoefficientsbetweenrheologicalPropertiesandQualitiesofjapanesespongeCakesandsugar-snapCookiesMadefromsoftWheatflourgrownintheunitedstates

QualityParameter japanesespongeCakevolume sugar-snapCookiediameter

P –0.639a ns

L 0.492b 0.522b

MPT ns 0.577b

MPH –0.692a –0.590b

FWA ns –0.667a

FPT –0.490b ns

Notes: P,Alveograph maximum overpressure; L,Alveograph length; MPT, Mixograph peak time;MPH, Mixograph peak height; FWA, Farinograph water absorption; FPT, Farinograph peaktime;ns,notsignificant.

a Significantatthe1%level.b Significantatthe5%level.

Source:AdaptedfromYamamoto,H.,Worthington,S.T.,Hou,G.,andNg,P.K.W.,Cereal Chemistry,73,215–221,1996.

52748.indb 13 2/6/08 2:24:37 PM



... Mixographandfarinograph

TheMixograph(NationalManufacturing,Lincoln,NE)andFarinograph(C.W.Bra-benderInstruments,Inc.,SouthHackensack,NJ)arebothmixersthatrecordchangesindoughpropertiesover time(AACCIMethods54-40Aand54-21, respectively).These instruments are able to give information regarding optimum dough waterabsorption,strength,mixingtime,andtolerancetoovermixing.Themaindifferencebetweenthetwoisinthegeometryofthemixers.TheMixographusesverticallyori-entedpinsthatmoveinaplanetarymotion,andtheFarinographusessigmoid-shapedmixingpaddles.TheMixographwasdevelopedtoprovidethemoreintensivemixingthatNorthAmericanwheatsrequire.ItisthereforemainlyusedthereaswellasinAustralia.TheFarinographiswidelyusedaroundtheworld(Ingelin1997).Hazenetal.(1997)reportedsignificantrelationshipsbetweenwire-cutcookiediametersandMixographpeaktime,andpeakheight.Uriyoetal.(2004)foundsignificantnegativecorrelationsbetweenFarinographwaterabsorptionandcookiediameter,andwithcakevolume, inproductsmade fromsoft redwinterwheat.Cake tendernesswascorrelated with Farinograph departure time and mixing stability. Yamamoto andcoworkers(1996)alsoreportedanegativecorrelationbetweencookiediameterandFarinographwaterabsorptionalongwithanegativecorrelationofcookiediametertoMixographpeakheight(Table1.2);therewasapositivecorrelationbetweencookiediameterandMixographpeaktime.OtherworkershavealsocorrelatedFarinographandMixographmeasurementswithvariouscakeandcookiequalities(FinneyandBains1999;Nemethetal.1994;Uriyoetal.2004).

1.5.4 ProduCTsrequirinGweakerProTeins

Muchresearchinthepasthasbeenfocusedondevelopingproceduresforsoftwheatquality evaluation. However, no test has proven more satisfactory than a bakingtest,whichisanall-inclusivetest.MostU.S.Easternsoftwheatshavebeentestedforcakeandcookie-makingqualities.MostofthesetestshavefollowedstandardAACCImethods.

... Cookies

Thesugar-snapcookiebakingtest(AACCIMethod10-52)wasconsidered“thestan-dard”cookietestformanyyearsandhasbeenusedtoevaluateflourforproductssuchascookies,crackers,cakes,andpies(Gaines2004).Floursthatproducecookieswithlargerspreadandsoftertexturearefavored.Astherearefewersugar-snap-typecookiesonthemarket,thewire-cutcookiebakingtestwasdevelopedwhichutilizesacookieformulationthatmorecloselyreflectsthecommercialwire-cutcookiefor-mulation(AACCIMethod10-54;SladeandLevine1994)(Table1.3).Gainesetal.(1996b)comparedthesugar-snapandwire-cutcookieformulationsandfoundthateventhoughbothtestswerecapableofevaluatingspread,thewire-cutcookiesbet-terreflecteddifferencesincookietexturebasedoninstrumentalhardnessevaluatedusinganInstronuniversaltestingmachine.

52748.indb 14 2/6/08 2:24:37 PM


Soft Wheat Quality

... high-ratioCakes

Thehigh-ratio(moresugarthanflour,wt:wt)cakebakingtest(AACCIMethod10-90)iscommonlyusedtoevaluatesoftwheatfloursforcakeproducts.Theimportantcharacteristicoftheflourusedinthesecakesisthattheymustbeabletocarry1.3to1.4timestheirweightinsugar(seeTable1.4forformula).Toaccomplishthis,cakeflourischlorinatedtomodifytheflourcomponents.Bakedcakesarescoredbasedontheirvolume,contour(symmetry),cellstructure,grain,texture,color,andflavor.

taBle.

ComparisonofMicroWire-Cut(aaCCIMethod0-)andMicrosugar-snap(aaCCIMethod0-)Cookieformulations

formulation

Ingredient Wire-Cut(g) sugar-snap(g)

Sucrose 12.8 24

Brownulatedsugar 4.0 —

Nonfatdrymilk 0.4 1.2

NaCl 0.5 0.18

Sodiumbicarbonate 0.4 0.4

SolutionAa na 0.32

SolutionBb na 0.20

Shortening 16.0 12

High-fructosecornsyrup 0.6 —

Ammoniumcarbonate 0.2 —

Water Variable Variable

Flour 40.0(13%m.b.) 40(14%m.b.)a SolutionA:7.98%sodiumbicarbonateinwater.b SolutionB:10.16%ammoniumchlorideand8.88%NaClinwater.

taBle.

high-ratioWhitelayerCakeformulation(aaCCIMethod0-0)Ingredient Weights(g) WeightPercent(flourBasis)

Flour(14%m.b.) 200.0 100.0

Sugar 280.0 140.0

Shortening 100.0 50.0

Nonfatdrymilk 24.0 12.0

Driedeggwhites 18.0 9.0

NaCl 6.0 3.0

Bakingpowderandwater Variable Variable

52748.indb 15 2/6/08 2:24:38 PM



1.5.5 ProduCTsrequirinGsTronGerProTeins

Crackersandnoodlesareeconomicallysignificantcategoriesofproducts thataremadewithsoftwheatflour,thoughtheyarenotsweetgoods.Crackersreferredtoin the followingsectionareproducedby fermentationwithyeast tomake saltineandsimilarcrackers.FlourqualityfornoodleproductionisespeciallyimportantforexportofwheattocountriesintheFarEast.

... Crackers

Crackersrequirestrongerglutenthanothersoftwheatproductsandareoftenmadefromblendsofbothhardandsoftwheatflours.Thisstrongerglutenisnecessarytogivestructuretocrackersastheyarefermentedandsheeted.Thereisstillnooffi-cial testmethod for evaluatingflours for cracker-bakingpotential, although therearepublishedproceduresusingatwo-stagespongeanddoughapproachtomakingcrackers(DoescherandHoseney1985;PizzinattoandHoseney1980).Thisinvolvesfermentationofasponge(containingyeast,water,and60to70%oftheflour)for16to18hfollowedbyadditionoftheremainingingredientsandfermentationofthedoughforanother6h(CreightonandHoseney1990;DoescherandHoseney1985;RanhotraandGelroth1988).However,durationofthesetestprocedureslimitsthenumberofsamplesthatcanbeevaluatedbyanoperatorinagiventime.Leeetal.(2002)developedapracticalone-stageprocedurethatenablesanoperatortoevalu-ate15samples,ascomparedtoabout6sampleswiththetwo-stageprocedures,ina48-hperiod.Althoughthetwotypesofproceduresyieldedslightlydifferentbakingresults,thetrendswerethesameforadiversegroupoffloursamplesexamined(Leeetal.2002).Strongerdoughsmadecrackersthatwerethicker,larger,andinhardertexturethancrackersmadefromweakerdoughs.

... noodles

Asiannoodlesareanotherproduct,oftenmadefromblendsofhardandsoftwheatflours,whichrequirestrongergluten.TherearetwobasickindsofAsiannoodles:whitesalted(Udon)andalkalinenoodles(Bettge2004).Udonnoodlesareusuallymadefromflourwith8to10%proteincontentandalkalinenoodles10.5to12%pro-tein(Junetal.1998).ThetextureofAsiannoodlesisrelatedtoflourproteincontentandstarchcharacteristics.TheproteincontentofflourwaspositivelycorrelatedwithnoodlechewinessinastudybyBaiketal.(1994b).Starchpastingpropertieshavebeenshowntoaffecttheoveralltextureofnoodles,includingsoftnessandelasticity(Bateyetal.,1997;Koniketal.1992).Anotherimportantnoodlequalitydetermi-nant,especiallywiththehigherpHofalkalinenoodles,isdiscolorationfromPPOactivity.TheWesternWheatQualityLaboratoryoftheUSDA-ARS(Pullman,WA)hasdevelopedmethodsfortestingalkalineandsaltedAsiannoodles.Noodlesareproducedonalaboratory-scalemachineandareevaluatedbasedoncolor,texture,andyield.

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Soft Wheat Quality

. effeCtsofflourCoMPonentsonCooKIes

Flourproteins,starches,pentosans,andlipidsallaffectthesizeorspreadofcookiesaswellastheirtextureandappearance.Withthewidevarietyofcookiesproduced,thesecomponentsneedtobetakenintoaccountwhenselectingflour.

1.6.1 ProTeins

Softwheatflourwithlowproteincontentistypicallyusedintheproductionofcook-iesbecauseofthedeleteriouseffectsonqualityassociatedwiththehigherproteincontentinhardwheats.Sugar-snapcookiesmadefromhardwheatflourareusuallythicker,harderintexture,andhaveasmallerdiameter(MillerandHoseney1997).Sugar-snapcookiediameterperunitofflourproteinwasnegativelycorrelatedwithprotein content in a studybyYamamoto et al. (1996) (Figure1.3).Using awire-cutcookieformulation,Gainesetal.(1996b)foundanegativecorrelationbetweenproteincontentandcookiediameterandapositivecorrelationwithcookieheight(Table1.5). Harder texture was also positively correlated with increased proteincontentinthisstudy.Higherflourproteincontenthasbeencorrelatedwithreducedcookiespreadinotherstudiesaswell(Gaines1985;KaldyandRubenthaler1987).However,somestudieshavefoundapoorcorrelationbetweencookiequalityandproteincontent(Abboudetal.1985a;Yamazaki1954).

Cookie spread is a functionof the spread rate and the set time (Abboud et al.1985b;MillerandHoseney1997).Ascookiedoughisheated,thedecreaseinviscosity

1.4

1.3

1.2

1.1

1.0

0.96.5 7.0 7.5 8.0 8.5 9.0

Protein (%)

Cook

ie D

iam

eter

(cm

) / F

lour

Pro

tein

fIgure. Relationship between protein content and sugar-snap cookie diameter perunitflourproteinincookiesmadefrom17softwheatcultivarsgrownintheUnitedStates.(AdaptedfromYamamoto,H.,Worthington,S.T.,Hou,G.,andNg,P.K.W.,Cereal Chemis-try,73,215–221,1996.)

52748.indb 17 2/6/08 2:24:39 PM



allowsforthecookietospreaduntilitrisesinviscosityandsets.Althoughglutenisnotdevelopedduringmixing(MillerandHoseney1997),itsglasstransitiontemperatureplaysanimportantpartincookiesettime.Whentheglutenreachesitsglasstransitiontemperature,theviscosityofthedoughincreasesandspreadingstops(Doescheretal.1987;Milleretal.1996).MillerandHoseney(1997)examinedthesettimeofdiffer-enthardandsoftwheatfloursandfoundthatwithinagroupofhardorsoftwheats,proteincontentaffectedthesettime.However,thedifferencesinproteincontentalonewerenotenoughtofullyexplainthedifferencesbetweenthehardandsoftwheatflourgroups.Workhasalsobeendonetoidentifyspecificcomponentsofflourproteinsthatmay affect cookiequality.Huebner et al. (1999) fractionatedgliadins andgluteninsubunitsusingsize-exclusionhigh-performanceliquidchromatography(HPLC).Theyfoundthatflourswithgluteninsubunits5+10madebetter-qualitycookies.Souzaetal.(1994)foundthatthegluteninstrengthscore,developedbyPayneetal.(1987)toevalu-atebreadflours,wasnegativelycorrelatedwithcookiediameter.Houetal.(1996b)separatedthehigh(Asubunits)andlow(BandCsubunits)molecularweightgluteninsubunitsandfoundthattheratioofthequantitiesoftheBtoCsubunitswasrelatedtosugar-snapcookiediameterinflourfromsoftwhitewinterwheat.

1.6.2 sTarCh

Therateofspreadinghasbeenfoundtobefasterincookiesmadefromsoftwheatflourcomparedtocookiesmadefromhardwheatflour(Abboudetal.1985b;Milleretal.1996;MillerandHoseney1997).Afasterspreadrateallowsthecookietospreadtoalargerdiameterbeforesettingoccurs.MillerandHoseney(1997)measuredthespreadrateofcookiesmadefromsoftwheatflourtobe7.8mm/mincomparedto4.6mm/minincookiesmadewithhardwheatflour.Thehardwheatflourswerefoundtocontainhigherlevelsofsolublestarchthanthesoftwheatflours.Removalofthesolublestarchfromhardwheatfloursresulted indecreaseddoughviscositiesandincreasedcookiespreadrates.However,althoughtheamountofsolublestarchcouldexplain thedifferencebetween thehardandsoftwheatflourgroups, it couldnotfullyexplainthedifferenceinspreadrateswithinthegroups.Higherlevelsofdam-agedstarchinmilledhardwheatwerealsoattributedtobeingpartofthedifferenceinspreadratebetweenhardandsoftwheatfloursbyMillerandHoseney(1997).

taBle.

CorrelationCoefficientsbetweenflourProteinContentandWire-CutCookieQualityCharacteristics

Parameter CorrelationCoefficient

Diameter –0.57a

Height 0.64a

Hardness 0.79a

a Significantatthe5%level.

Source:AdaptedfromGaines,C.S.,Kassuba,A.,andFinney,P.L.,Cereal Foods World,41,155–160,1996.

52748.indb 18 2/6/08 2:24:39 PM


Soft Wheat Quality

During baking, minimal gelatinization of starch occurs due to the low watercontentofcookiedough,asshownbydifferentialscanningcalorimetry(AbboudandHoseney1984).However,damagedstarch,withitsgreaterwater-holdingcapability,isknowntonegativelyaffectcookiediameter.DonelsonandGaines(1998)increasedthedamagedstarchcontentofhardandsoftwheatfloursusedtomakesugar-snapcookiesthroughtheadditionofball-milledandpregelatinizedstarch.Forbothhardandsoftwheatflours,theadditionofdamagedstarchledtoanincreaseinalkalinewaterretentioncapacityandadecreaseincookiediameter.Theyalsomadecook-ieswith100%oftheflourreplacedbycombinationsofprimeanddamagedstarch.Thesoftwheatstarchproducedcookieswithlargerdiametersthanthehardwheatstarchatallofthedifferentlevelsofstarchdamagestudied.Additionally,thehardwheatstarchdoughshadgreaterstiffnessthanthosemadefromsoftwheatstarch.Theauthorsconcludedthatthereisafundamentaldifferencebetweenhardandsoftwheatstarchesthatleadstotheirdifferentperformancesincookiebaking.

1.6.3 PenTosans

With their ability to absorb large amounts of water, pentosans also affect cookiequality.Yamazaki(1955)foundthattheadditionofpurifiedstarchtailingsfractions,rich inpentosans, increased thehydration abilityof softwheatflour and reducedcookie spread.BettgeandMorris (2000)measured total,water-soluble,andgrainmembranepentosansin13softwheatfloursamples.Theamountoftotalpentosanshadthelargestnegativecorrelationwithsugar-snapcookiespreadfollowedbythewater-solubleandgrainmembranepentosans.Thegrainmembranepentosanswerealsohighlypositivelycorrelatedwithalkalinewaterretentioncapacity.Abboudetal.(1985a),ontheotherhand,reportedapoorcorrelationbetweenpentosancontentandcookiediameter.Sucrosesolventretentioncapacity,whichisassociatedwithpento-sans,wasnegativelycorrelatedwithsugar-snapcookiespreadbyGaines(2004),eventhoughintheirstudy,alkalinewaterretentioncapacitywasnot.Usingsucrosesol-ventretentioncapacityalongwithflourproteincontentandmillingsoftness,Gaines(2004)wasalsoabletogeneratearegressionequationtopredictcookiediameter.

1.6.4 liPids

Studiesinvolvingtheremovalandreconstitutionofflourlipidshaveshownthattheyareimportanttocookiespread,topgrain(an“islanding”patternformedonthesur-faceofsugar-snapcookies),andstructure.Coleetal.(1960)bakedcookieswithflourthathadbeenextractedwithwater-saturatedbutanolandfoundthatthecookieshaddecreaseddiameters.Whenthelipidswerereplaced,thecookiespreadwasreturnedtonormal.Kisselletal.(1971)extractedfreelipidsfromsoftwheatflourandfrac-tionatedthemintopolarandnonpolarfractions.Theywerethenreintroducedintotheflourandbakedintosugar-snapcookies.Toachievenormalcookiespreadandtop grain, both the polar and nonpolar fractions were needed. Interchanging thelipidsbetweendifferentvarietiesofwheatflourdidnotaffecttheresults,indicatingthatthepresenceofthemixedlipidsismoreimportantthanthesource.FractionationstudiesbyClementsandDonelson(1981),on theotherhand,determined that thepolarlipids(digalactosyldiglycerideandphosphytidylcholinealongwithglycolip-

52748.indb 19 2/6/08 2:24:40 PM



ids)weremoreimportanttosugar-snapcookiespreadthanthenonpolarlipids.Theinternalstructureofcookiesmadefromdefattedflour isalsonegativelyaffected;thesecookieshavelargercellsasopposedtothefinerandmoreuniformcellstruc-turefoundingood-qualitycookies(Clements1980).

. effeCtsofflourCoMPonentsonCaKes

Cakebattersareaeratedemulsionsoffatinwaterthatexpandduringbakingandsetintoasoft,porousgel(Mizukoshietal.1980;Shelkeetal.1990).Duringtheinitialphaseofbaking,thereisadropinbatterviscosityasshorteningmeltsandsugarsbecomedissolved.Thisisfollowedbyarapidriseinviscositywhenstarchbecomesgelatinized,absorbingfreewaterandsettingthecake(Howardetal.1968;Shelkeetal.1990).Flourproteinsandlipidsalongwiththeflourparticlesizealsoaffectcakequality.

1.7.1 FlourParTiClesize

Whenmeasuredbylaserdiffraction,softwheatflourhasbeenfoundtohaveamuchhigher percentage of particles below41µm in size than that of hardwheat flour(Hareland 1994). The particle sizes of various soft wheat flours have been nega-tivelycorrelatedtocakevolume(Yamamotoetal.1996;YamazakiandDonelson1972).Inadditiontovarietaldifferencesinparticlesizeproducedbynormalmill-ing,researchhasshownthatfurtherreductionofparticlesizethroughpostmillingprocessing(pin-millingandair-classification)canimprovethevolumeandqualityofcakes(Chaudharyetal.1981;GainesandDonelson1985a;Milleretal.1967).Althoughreducingparticlesizeisbeneficial,itisimportanttolimitstarchdamage,asdamagelevelsgreaterthan5%havebeennegativelycorrelatedwithcakequality(Milleretal.1967).

1.7.2 ProTeins

Higherproteincontentinflourisgenerallyassociatedwithpoorerqualityforcakebaking.AccordingtoKaldyandRubenthaler(1987),flourhighinproteinorwithstrongglutenresultsincakeswithlowervolumeandcoarsertextureduetoproteindisruptionofthefoamstructureincakebatter.IntheirstudyofCanadiansoftwhitewinterandspringwheats,theyfoundasignificantnegativecorrelationbetweenflourproteincontent,Japanesespongecakevolume,andoverallcakescore.Yamamotoetal. (1996)alsofoundanegativecorrelationbetweenflourproteinandJapanesesponge cake volume per unit protein (Figure1.4). Gaines and Donelson (1985b)found that thevolumeand tendernessofwhite layer cakeswerenot significantlyaffectedbyproteincontent,although thoseofangel foodcakeswere.However,adifferenceofover2%proteinwasneededtoseeaneffectintheangelfoodcakes.Althoughanexcessofproteinmayharmcakequality,solubleproteins(bothfromtheflourandfromothercakeingredients)arestillneededforthermalstabilityofthe cake foamstructure (Howardet al. 1968).Protein composition in addition tocontentwasshowntobeimportanttoJapanesespongecakevolumeinworkbyHouetal.(1996b).Thepresenceofhigh-molecular-weightglutenin(HMW-GS)subunit

52748.indb 20 2/6/08 2:24:40 PM


Soft Wheat Quality

1insoftwheatflourresultedinlargercakevolume,whilethepresenceofHMW-GSsubunit2*resultedinsmallervolume.

1.7.3 liPids

Lipidsmakeuponlyasmallfractionofflour;however,theyareimportanttocakevolumeandtexture.SpiesandKirleis(1978)foundthatextractionoffreeflourlipidsreducedvolumeandcausedpoorertextureincakesmadewithamodifiedwhitelayercakeformula.Reintroductionofthelipidsrestoredmostofthecakequalities.Inter-changingthelipidsbetweendifferentvarietiesofwheatdidnotaffect theresults,indicating that the presence of lipids is more important than the source. Takeda(1994) extracted free lipids fromflour, resulting in reduced sponge cakevolume.Thefreelipidswerealsofractionatedintopolarandnonpolarfractions.Reintroduc-tionofthepolarlipids(monogalactosylanddigalactosyldiglycerides)returnedthecakevolumetoitsnormalsize,whilethenonpolarfractionshadonlyminoreffects.SimilarresultswerereportedbySeguchiandMatsuki(1977a).

. flourChlorInatIon

Toproducegood-qualityhigh-ratiocakes,chlorinationofflourisnecessary.Cakesmadefromnonchlorinatedflourhavepoorvolume,contour,crumbgrain,andtex-ture(Donelsonetal.2000;Montzheimer1931;Smith1932).Chlorinetreatmentalsoimprovesmouthfeelofcakes,makingcakesdrierandlessstickyorgummy(Kis-

7.06.5 7.5 8.0 8.5 9.0

180

170

160

150

140

130

120

Protein (%)

Cak

e Vo

lum

e (c

c) /

Flou

r Pro

tein

fIgure. RelationshipbetweenproteincontentandJapanesespongecakevolumeperunitflourprotein incakesmade from17softwheatcultivarsgrown in theUnitedStates.(AdaptedfromYamamoto,H.,Worthington,S.T.,Hou,G.,andNg,P.K.W.,Cereal Chemis-try,73,215–221,1996.)

52748.indb 21 2/6/08 2:24:41 PM



sellandYamazaki1979;SeguchiandMatsuki1977b).ChlorinationisusuallydonewithchlorinegasandcanbemonitoredbyadropinpHofflour.FlouristypicallychlorinatedtoapHrangeofabout4.5to5.2(Goughetal.1978).Starch,lipids,andproteinsareallaffectedbyflourchlorination.

1.8.1 sTarCh

Fractionation,interchange,andreconstitutionstudiesofnonchlorinatedandchlori-natedflourshaveconfirmedthattheeffectsofchlorinationonstarchareimportantto cake quality. Cakes made from chlorinated flour with the starch interchangedwiththatfromnonchlorinatedflourhadsmallervolumesandpoorercakequalities(JohnsonandHoseney1979a;Sollars1958).Theoppositewastruewhenexchang-ingchlorinatedstarchintononchlorinatedflour.GainesandDonelson(1982)usedamodifiedViscographtoexaminetheviscosityofcakebattersmadewithchlorinatedandnonchlorinatedfloursduringheating.Theapparentviscosityofheatedbattersincreasedfasterinbattersmadefromchlorinatedflourcomparedtononchlorinatedflour.Chlorinatedflourbattersalsoshowedgreaterexpansionduringbaking.Theseresultswere inagreementwith results fromKulpetal. (1972).Accelerated thick-ening of batters allows for improved setting and retention of larger cake volume(Donelsonetal.2000).

Donelson(1990)fractionatedchlorinatedandnonchlorinatedfloursandfoundthatthechlorinatedstarchfractionhadincreasedalkalinewaterretentioncapacity.Theseresultswererelatedtodecreasedsugar-snapcookiespreadinhisexperiment.Inadditiontobindingmorewater,chlorinatedstarchbindsmoreoilasaresultofincreasedstarchgranulehydrophobicity(Seguchi1984).Theoxidativedepolymer-izationofstarchthatoccursduringchlorinationhasbeeninvestigatedasoneofthereasons for these changes in starch properties (Huang et al. 1982; Johnson et al.1980).Varriano-Marston (1985)hypothesized that theoxidativedepolymerizationincreased thecapillarysizeofstarchgranules, leading to the increasedabilityofchlorinatedstarchtobindwaterandoil.

1.8.2 liPids

Variousstudieshavedeterminedthattheeffectofchlorinationonlipidsisimportanttocakequality.Kisselletal.(1979)chlorinatedflourstopH5.2,4.8,and4.0andthenextractedthefreelipidswithhexane.Whitelayercakevolumewasreducedincakesbakedwithoutlipids;however,thenormalvolumewasrestoreduponreadditionoftheextractedlipids.FlourchlorinatedtopH4.8performedthebest.Byinterchang-inglipidsfromachlorinatedflourintoanonchlorinatedone,Donelsonetal.(1984)wereabletoincreasehigh-ratiocakevolumetothatofthechlorinatedflour.Incon-trast,Johnsonetal.(1979),afterconductingalipidinterchangestudy,cametotheconclusionthatalthoughthepresenceoflipidsisimportant,theeffectofchlorinationonthemisnotimportanttocakequalityincakesbakedusingKissell’sleancakeformulation(Kissell,1959).InthestudyofJohnsonetal.(1979),cakesbakedfrombothchlorinatedandnonchlorinatedflourswiththeirlipidsextractedhadpoorgrain.Byaddingeitherofthelipidfractionsbacktothechlorinatedflour,theywereabletorestorethebakingproperties.

52748.indb 22 2/6/08 2:24:41 PM


Soft Wheat Quality

1.8.3 ProTeins

ThefractionationandinterchangestudiesofSollars(1958)foundthatchlorinationofgluten and starchwasof almost equal importance for theproductionofwhitelayercakes.Chlorinationofglutenhadaneffectonyellowlayercakesaswell,buttoalesserextent.Tsenetal.(1971)reportedthatchlorinationofflourincreasestheextractabilityofproteinsbywaterandaceticacid,andthat this increasedproteinsolubilitymaybepartoftheimprovingeffectsofchlorinetreatmentonflour.Thechanges inprotein extractabilitywere attributed to the actionsof chlorinebreak-inghydrogenbonds,cleavingpeptidebonds,degradingaminoacids,andoxidizingsulfhydrylbonds.

Theeffectofchlorinationonincreasingthehydrophobicityofproteinsinfloursmayalsobeimportant.Seguchi(1985)foundthatchangesinthehydrophobicityofstarchgranuleswereduetoconformationalchangesinsurfaceproteinsofthestarchgranules,andlater,thatchlorinationalsoresultedinanincreaseintheamountofproteinextracted(Seguchi1990).Sinhaetal.(1997)extractedgliadinsfromflourchlorinatedtopH4.8and4.3;gliadinproteinhydrophobicity,asmeasuredbyfluo-rescence spectroscopy, increased with chlorination (Figure1.5). Reversed-phaseHPLCresultssuggestedthattheincreasesinhydrophobicitywereduetoconforma-tionalchangesintheproteins(Sinhaetal.1997).

12

10

8

6

4

2

0

NonchlorinatedpH 4.8pH 4.3

Caldwell Dynasty Frankenmuth Lewjain

Hyd

roph

obic

ity In

dex

x10

fIgure. Relative hydrophobicities of gliadins extracted from chlorinated and non-chlorinatedsoftwheatflours,measuredbyfluorescencespectroscopy.(AdaptedfromSinha,N.K.,Yamamoto,H.,andNg,P.K.W.,Food Chemistry,59,387–393,1997.)

52748.indb 23 2/6/08 2:24:42 PM



1.8.4 alTernaTivesToChlorinaTion

Overtheyears,alternativestochlorinationhavebeenexploredasconcernfor thesafetyofchemicallyprocessedfoodshasgrown.RussoandDoe(1970)improvedcakevolumebyheatingnonchlorinatedflour;however, thisalsoresultedincakeswithpoortexture.Theadditionofingredientssuchasstarch,eggalbumin,xanthangum,L-cysteine,andhydrogenperoxideplusperoxidasehavealsobeentestedfortheirabilitiestocompensateforalackofchlorination(JohnsonandHoseney1979b;RussoandDoe1970;Thomassonetal.1995).Intheircakeformulation,Donelsonetal.(2000)replacednonchlorinatedflourwitheithercommercialhardwheatstarchoralaboratory-producedsoftwheatstarchatalevelequaltotheareaunderanRVApastingcurvemade fromchlorinatedflour.Thiswasdone to tryandachieve theviscosity-modifyingpropertiesnormallyassociatedwithchlorination.Eggalbumin,soy lecithin, andxanthangumwerealsoadded to their cake formula to improvetextureandcontour.Theresultsafterbakingvarioustypesofcakeswereequaltoorbetterthanthosemadewithchlorinatedflours.Mostimportantly,thecakeshadcrumbswithgoodtextureratherthanthegummytexturesofcakesmadewithnon-chlorinatedflour.Theozonetreatmentofflourhasalsorecentlybeeninvestigatedwithpromisingresults(ChittrakornandMacRitchie2006).

. ConClusIon

Thedifferentcomponentsofsoftwheatflourcollectivelyplayaroleinitsquality.Softerkerneltextureandlowerproteincontentaretypicallyfavoredforsoftwheatproducts.Starchesandlipidsserveimportantfunctionsinbakedproductssuchascakesandcookies.Understandingwheatflourcompositionandhowqualityismea-suredprovidesagoodbaseforfurtherresearchandstudyofsweetgoods.

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2 Functions of Ingredients in the Baking of Sweet Goods

Dasappa Indrani, Gandham Venkateswara Rao

Contents

2.1 Introduction................................................................................................... 322.2 FunctionsofSugar........................................................................................ 33

2.2.1 YeastedDoughs................................................................................. 332.2.2 Cakes..................................................................................................342.2.3 Cookies..............................................................................................342.2.4 Biscuits............................................................................................... 35

2.3 FunctionsofFat............................................................................................. 352.3.1 YeastedDoughs................................................................................. 352.3.2 Cakes.................................................................................................. 352.3.3 Cookies.............................................................................................. 352.3.4 Biscuits...............................................................................................36

2.4 FunctionsofEggs..........................................................................................362.4.1 YeastedDoughs.................................................................................362.4.2 Cakes..................................................................................................362.4.3 Cookies.............................................................................................. 37

2.5 FunctionsofLeaveningAgents..................................................................... 372.5.1 YeastedDoughs................................................................................. 382.5.2 Cakes.................................................................................................. 382.5.3 Biscuits............................................................................................... 38

2.6 FunctionsofWater........................................................................................ 382.6.1 YeastedDoughs................................................................................. 382.6.2 Cakes.................................................................................................. 392.6.3 Biscuits............................................................................................... 39

2.7 FunctionsofSalt........................................................................................... 392.7.1 YeastedDoughs................................................................................. 392.7.2 Cakes.................................................................................................. 392.7.3 Biscuits............................................................................................... 39

2.8 FunctionsofNonfatDryMilk......................................................................402.8.1 YeastedDoughs.................................................................................402.8.2 Cakes..................................................................................................402.8.3 BiscuitsandCookies..........................................................................40

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2.9 FunctionsofAdditives..................................................................................402.9.1 OxidizingAgents...............................................................................402.9.2 ReducingAgents................................................................................402.9.3 SurfactantsandEmulsifiers...............................................................402.9.4 Enzymes............................................................................................. 422.9.5 VitalWheatGluten............................................................................ 422.9.6 Hydrocolloids..................................................................................... 42

2.10 RecentStudiesontheEffectsofIngredientsonQualityofCakesandBiscuits.................................................................. 43

2.11 Conclusion.....................................................................................................44References................................................................................................................ 45

. IntroduCtIon

Sweetgoodsare,asthenameimplies,sweettotaste,madefromaformulahighinsugar.Theingredientsofsweetbakedgoodsareflour,shortening,eggs,nonfatdrymilk,yeast,salt,leaveningagents,additives,flavors,water,andvariousotherenrich-ingingredients,andsoforth.ThepercentagelevelsofingredientsusedindifferentsweetgoodsarepresentedinTable2.1.Eachoneoftheseingredientshasitsownroleandfunctioninthepreparationoftheproduct.Theroleofingredientswillvaryfromonetypeofproducttoanother.

Among thevariousyeast-raisedgoodsmade inbakeries, sweetgoodsare themostcommon.Someoftheexamplesofsweetgoodsareyeast-raisedsweetbreadsandrolls,cakes,biscuits,cookies,anddoughnuts. Yeast-raisedsweetdoughissimi-lartobreaddoughbutcontainshighsugarandfatlevels.Mostsweetgoodsusewhiteflourratherthanwholewheatflour,becausewholewheatflourcanresultinreduced

taBle.

formulations,Products,andIngredientsIngredients yeasted

sweetdoughCakes Biscuits Cookies doughnuts

Wheatflour 100 100 100 100 100

Compressedyeast 2–2.5 — — — 2–5

Sugar 10–30 60–120 15–35 50–60 5–12

Fat/shortening 10–20 50–100 10–25 50–60 10–15

Eggs 5–10 50–100 — 10 5–10

Salt 1.5–2 — 0.5 — —

Nonfatdrymilk 5–10 2–5 2–5 — 4–8

Bakingpowder — — — — 1–2

Sodiumbicarbonate — — 0.5 — —

Ammoniumbicarbonate

— — 1.0 — —

Flavor — Variable Variable Variable Variable

Water Variable Variable Variable — Variable

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Functions of Ingredients in the Baking of Sweet Goods

volume.Thesweetnessinsweetbakedgoodsoftencomesfromsucrose.Onaflourweightbasistraditionallyknownasbaker’spercent,15to25%sugaristypicalfortheseproducts.Wholeeggsandmilksolidsareconstituentsofmostsweetdoughformulations.Theseingredientsaddrichness,flavor,andtendernesstotheproduct(Sharon,2000).

Additives are substances intentionally added to bakery products in smallerquantities,withaviewtoimprovethefunctionalperformanceoftherawmaterials,processingcharacteristics,appeal,palatability,qualityofproducts,andstoragesta-bility.Thevariousadditivescommonlyusedinbakingareoxidizingagents(potas-siumbromateorascorbicacid),reducingagents(cysteinehydrochloride,potassiummetabisulfite),vitalwheatgluten,enzymes(fungalα-amylase,protease),surfactantsand emulsifiers (glycerol monostearate, sodium stearoyl-2-lactylate, lecithin), andhydrocolloids(guargum,xanthan,hydroxylpropylmethylcellulose).

Discussedinthischapterarethefunctionsofsugar,fat,eggs,leaveningagents,water,salt,nonfatdrymilk,andadditivesinyeasteddoughs,cakes,cookies,andbiscuits.

. funCtIonsofsugar

2.2.1 yeasTeddouGhs

Sucroseisadisaccharidecomposedofaunitofdextroseplusaunitoffructose.Thetermsugariscommonlyusedtorefertosucrose.

Sugaristhemostcommonlyusedsweetenerinsweetdoughproducts.Sugar’smainfunctionistoprovidefoodforyeast.Whenaddedtoadough,sugarishydro-lyzed,orinverted,almostinstantlyintoglucoseandfructosebytheyeastenzymeinvertase.Yeastfermentsglucoseandfructoseintocarbondioxideandalcohol.Intypicalbreadproduction,2to3%sugarisadequatetosustainyeastactivity.Thisfoodsupplycancomefromaddedsugarorfromtheenzymaticconversionof thestarchtosugarorfromacombinationofboth.Eventhoughadequatecarbondioxidegasproductioncanbemaintainedwith2 to3%sugar,higher levelsarenormallyusedinsweetdoughformulations.Sugarthatremainsunfermentedbyyeastappearsasresidualsugarinthefinishedproducts.Residualsugartakespartincarameliza-tion and the Maillard reaction (i.e., the reaction between reducing sugar and theproteinsofflourtopromoterapidcolorandtasteformation).Sugarprovidessweettasteinbreadifusedabove6%(Dubois,1981b;Pyler,1988a).

Sweetgoodscontainhighlevelsofsugar,whichaffecttheactivityofyeast.Sugarhasastronginhibitoryeffectonthegassingpowerofyeast,causedbyhighosmoticpressureontheyeastcell.Sweetdoughwith20%sugarrequirestwotothreetimesmoreyeasttoobtainthesamegasproductionasthatoftypicalleandough.

Theamountofprotein,damagedstarch,andpentosansinflourwill influencetheamountofwaterthatitwillhold.Ultimately,watermakesupabout45%ofbreaddough.Duringmixing, it isknown thataconsiderableamountofwaterbecomesboundtomanydifferentingredients,suchasflour,sugar,andfat.Sugarwillservetodecreasethestrengthofglutendevelopmentduetoitscompetitionforwater.Itinhibitsthegliadin–glutenin–watercomplex,andglutenisthusweakened.

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2.2.2 Cakes

Cake isabakedbattermade fromwheatflour, sugar,eggs, shortening, leaveningagents,salt,nonfatdrymilk,flavors,andwater.High-ratiocakes,richinsugarandfat,areextensivelyusedinthebakingindustry.Cakebatterisacomplexfat-in-wateremulsioncomposedofbubblesasthediscontinuousphaseandegg–sugar–water–fatmixturesasthecontinuousphaseinwhichflourparticlesaredispersed(Mizukoshi,1983;NgoandTaranto,1986;Shelkeetal.,1990).

Sucroseisaprincipalingredientincakes.Itprovidesenergyandsweetness.Italsofacilitatesairincorporation.Itactsasatenderizerbyretardingandrestrictingglutenformation,increasingthetemperaturesofeggproteindenaturationandstarchgelatinization,andcontributingtobulkandvolume.

Inhigh-ratiocakeformulation,sugarresultsinagoodairincorporationleadingtoamoreviscousandstablefoam(Patonetal.,1981).Inaddition,sugaraffectsthephysical structureofbakedproductsby regulatinggelatinizationof starch.Delayinstarchgelatinizationduringbakingallowsairbubblestoexpandproperlyduetovaporbeforethecakesets(KimandSetser,1992;KimandWalker,1992).Attheconcentrationused incakes (55 to60%), sugardelays thegelatinizationofstarchfrom57to92°C,whichallowstheformationofdesiredcakestructure(SpiesandHoseney,1982;Beanetal.,1978).Sugar’sabilitytolimitthewateravailabletothestarch is thought to delay gelatinization (D’Appolonia, 1972; Derby et al., 1975;Hoseneyetal.,1977).AccordingtoSpiesandHoseney(1982),sugardelaysgelati-nizationthroughacombinationoftwoindependentmechanisms:loweringthewateractivityofthesolutionandinteractingwithstarchchainstostabilizetheamorphousregionsofthegranule.

Mizukoshi(1985)studiedtheeffectofvaryingsugarcontentonshearmodulusmeasured during cake baking, while keeping the proportion of other ingredientsconstant.Heshowedthatbelow20%,sugarhasnoeffectonshearmodulus,whereas30to40%sugarreducesitappreciably,revealingtheexistenceofathresholdvalueassociatedwiththevariationofsugarcontentintheformula.

2.2.3 Cookies

Thewordcookiemeans“littlecake.”Cookiesaremadefromsoftandweakflours.Theyarecharacterizedbyaformulathatishighinsugarandfatbutlowinwater.

Sugaraddssweetness,actsasatenderizingagent,andaffectsspread.Usingafarinograph,OlewnikandKulp(1984)observedthatanincreaseinsugarcon-centrationinacookiedoughreducesitsconsistencyandcohesion.Sucroseactsasahardeningagentbycrystallizingasthecookiecoolsandmakingtheproductcrisp.However,atmoderateamounts, itactsasasoftenerduetotheabilityofsucrosetoretainwater(Schanot,1981).Sugarmakesthecookedproductfragile,becauseitcontrolshydrationandtendstodispersetheproteinandstarchmol-ecules,therebypreventingtheformationofacontinuousmass(BeanandSetser,1992).

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2.2.4 BisCuiTs

Themajoringredientsofbiscuitdoughareflour,sugar,andfat.Thequalityofbis-cuits is governed by the nature and quality of the ingredients used. A variety ofshapesandtexturesmaybeproducedbyvaryingtheproportionoftheseingredients. Rotarymoldcookiesarecharacterizedbyaformulafairlyhighinsugarandfatandverylowintheamountofwater.

Sugar is important in the tasteandstructureofmostbiscuits.Theamountofsugarthatgoesintosolutiondependsontheparticlesizeofthesugarandinfluencesthespreadofbiscuitsandmachiningpropertiesofdoughtoagreatextent(MatzandMatz,1978).Vetter(1984)studiedtheeffectofsugarqualityanditsgrainsizeonbiscuitspreading.Vetterconcludedthatfinegrainsizeandahighconcentrationofsugarcontributetosignificantspreadingofthebiscuit.

Thelimitedamountofwaterusedinbiscuitformulation,andalsoitsnonavail-ability to protein and starch, particularly contributes to the crispness of biscuits.Theadditionofsugartotheformuladecreasesdoughviscosityandrelaxationtime.Sugar promotes biscuit length and reduces thickness and weight. Biscuits rich insugararecharacterizedbyhighcohesivestructureandcrisptexture.Increasingtheamountofsugargenerallyincreasesthespreadandreducesthethicknessofbiscuits(Kisseletal.,1973;Vetter,1984).

. funCtIonsoffat

2.3.1 yeasTeddouGhs

Fatorshorteningisusedatthelevelof5to15%inbreadmaking.Itisthoughtthatfatlubricatestheglutenfibrilsandmakesthedoughmoreextensible,therebyimprovingthegasretentioncapacityofthedough.Theadditionoffatfacilitatesdoughhandlingandprocessingandimprovesloafvolume,crumbgrainuniformity,tenderness,slic-ingproperties,andshelflife.

2.3.2 Cakes

The major function of fat is to entrap air into the batter during mixing. In cakebatter, thelargestpartof thefatcrystalsremainsin theaqueousphase.Whenairstartsexpanding,fatcrystalsadsorbedtotheair–waterinterfacemeltandtherebyrelease the fat–water interface forbubbleexpansion.A largenumberofadsorbedcrystalsreleasesufficientinterfacetoallowthebubblestoexpandwithoutrupturing(Brooker,1993a,1993b).

2.3.3 Cookies

Cookiedoughcharacteristicsdependonthequalityandquantityoftheingredientsusedintheformulation.Cookiedoughhashighpercentagesofsugarorshorteningandlimitedwater.Duringbaking,cookiediameterincreaseslinearlyandbecomessuddenlyfixed(Abboudetal.,1985;Milleretal.,1996;Yamazaki,1959).Thefinalcookiediameterdependsupontherateatwhichdoughspreadsanditssettingtime

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duringbaking.Cookiespreadratehasbeenreportedtobedependentondoughvis-cosity(Miller,1989;Yamazaki,1959).Theviscosityofcookiedoughdependsupontheratioof ingredientsusedinthecookieformula.Theadditionoffat influencesthetextureandtasteofcookies,makingthecookiescrispierbecausethisallowsthedoughtospreadasitcooksonthehotcookiesheet.

2.3.4 BisCuiTs

Fatisanessentialingredientinbiscuitmanufactureandisthelargestcomponentafterflourandsugar.Duringmixingof thebiscuitdough, fatactsasa lubricant; it alsocompeteswiththeaqueousphaseforthefloursurfaceandpreventstheformationofaglutennetworkinthedough(Wade,1988).Theadditionoffatsoftensthebiscuitdoughanddecreasestheviscosityandrelaxationtime.Fatcontributestoanincreaseinlengthandtoareductioninthicknessandweightofbiscuits,whicharethencharacterizedbyavariablestructureandareeasytobreak.Fatorshorteningcontributestotheplasticityofthedoughasalubricant.Whenpresentinlargequantities,itslubricatingeffectissopronouncedthatverylittlewaterisneededtoachieveasoftconsistency.Whenmixedwiththeflourbeforeitshydration,thefatpreventstheformationofaglutennetworkandproducesless-elasticdough.High-elasticdoughisnotdesirableinbiscuitmaking,becauseitshrinksafterlamination(MenjivarandFaridi,1994).Starchswellinganditsgelatinizationarealsoreducedathighlevelsoffat,givingacrisptexture.Fatinflu-encesthedoughmachinabilityduringprocessing,thedoughspreadaftercuttingout,andthetexturalandgustatoryqualitiesofthebiscuitafterbaking(Vetter,1984).

. funCtIonsofeggs

2.4.1 yeasTeddouGhs

Eggsinyeasteddoughsincreasenutritivevalue,improveflavorandtexture,producecolor incrumbandcrust, actasabindingagent tohold the ingredients together,aid in leavening, contribute to the emulsifying action due to the presence of thenaturalemulsifierlecithin,andproduceasoftercrumbbecauseofthefatandothersolids.Eggscontain73to75%moisture,havethenaturalabilitytobindandretainmoisture,andhenceimprovequality.Eggsareanimportantsourceofiron,calcium,phosphorus, vitamin A, vitamin D, thiamine, and riboflavin, and they supply allessentialaminoacids(Pyler,1988b).

Thecomplexcompositionofeggsimpartsnumerousfunctionaleffectsonbakedproducts.Theloafvolumeadvantageimpartedbyeggsdocumentedforsweetbakedgoodsmayrelatetoincreaseddoughwatercontentortheemulsifying,coagulating,andleaveningactionofwholeeggs(Forsythe,1970).

2.4.2 Cakes

Eggscontributestructuretoabakedproduct.Theymayservetodothisthroughtheircontributionofheat-denaturedproteins,steamforleavening,ormoistureforstarchgelatinization.Eggwhitehastheabilitytoformfoamsthatarestableenoughtosup-portlargequantitiesofflourorsugar.Thesefoamsmustbecapableofholdingthe

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otheringredientsuntilheatcoagulationcanoccurintheovenandastableproteinmatrixdevelops.Globulinsareprimarily responsible for loweringsurface tensionand increasing viscosity where air gets incorporated. As foam develops, bubblesbecomesmaller,thesurfaceisgreatlyenlarged,ovomucin(protein)undergoessur-facedenaturationtoformasolidfoam,andthevolumeoffoamincreases.Ovalbu-min,whichisreadilyheatcoagulable,setsupinheatandsupportsmanytimesitsweightofsugarandflour(MacDonneletal.,1955).

Eggsmaycontribute liquid toaproductandthusserveasa toughener. It isatoughenerpartiallyduetoitscontributiontogelatinizationofstarchandfordevel-opmentofgluten.Theeggwhiteportionappears tobeparticularlyeffectiveasatoughener.Actually,theyolkservesasatenderizerprobablyduetoitsfatcontent.Eggalsocontributes to leaveningaction through theemulsificationof fat andairincorporation,thefoamingaction,andthecontributionofwatertosteam.Eggyolkisalsoarichsourceofemulsifyingagentandthusfacilitatestheincorporationofair,inhibitsstarchgelatinization,andcontributestoadesirablegoldencolorthatgivesrichappearanceandflavor(Pyler,1988b).

2.4.3 Cookies

Eggshelpinpuffing,emulsifyingthedough,andbringingthewaterandfatphasestogethertoresultinacreamierandsmoothertextureincookies.Eggwhiteshaveadryingeffectandcontributetothestructureorshape.

. funCtIonsofleavenIngagents

Leavening isdefinedas a raisingaction that aeratesdoughorbatterduringmix-ingandbakingsothatthefinishedproductsaregreaterinvolumeandsuperiorintexture.Leaveningactioninabakedproductmaybeduetomechanicalleavening,biologicalleavening,chemicalleavening,andwatervapor.

Inmechanicalleavening,airisincorporatedbycreaming,beating,orwhiskingbyhandormachinethefat,sugar,andeggs.Cakes,spongegoods,andmeringuesareexamplesofmechanicalaeration.Inbiologicalleavening,thebaker’syeast(Sac-charomyces cereviseae)convertssimplesugarstocarbondioxideandalcohol.Thiscarbondioxideisresponsiblefortheleaveningofbreadsandotherfermentedbakeryproducts.

Chemicalleaveningincludestheuseofchemicalssuchasbakingsoda,ammo-niumbicarbonate,andbakingpowder.Bakingsoda,alsoknownassodiumbicarbon-ate,isusedinrecipesthatcontainanacidicingredient,suchasvinegar,buttermilk,chocolate, honey, or fruits.Baking soda liberates carbondioxidewhenheatedorwhenmixedwithanacid,eitherhotorcool.Ammoniumbicarbonateiscommonlyknownasvol,derivedfrom“volatilesalt,”becauseofitscompletedissociationintocarbondioxidegas,ammoniagas,andwater.Itisimportantthatalloftheammoniaisdrivenoffduringbakingorunpleasanttastesareencountered.Ammoniumbicar-bonateisthereforenotsuitableasaleaveningagentinanyproductthatleavestheovenwithmorethan5%moisture(Dubois,1981a;KichlineandConn,1970).

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Baking powder is a dry chemical leavening agent used in baking. There areseveral formulations—allcontainanalkali, typicallysodiumbicarbonate,andanacidtogetherwithstarchtokeepitdry.Whendissolvedinwater,theacidandalkalireact and emit carbon dioxide gas, which expands existing bubbles to leaven themixture.Therearetwotypesofbakingpowders—singleactinganddoubleacting.Bakingpowdersthatcontainonlythelow-temperatureacidsalts,suchascreamoftartar,calciumphosphate,andcitrate,arecalledsingleacting.Double-actingbakingpowderscontaintwoacidsalts:onereactsatroomtemperature,producingariseassoonasthedoughorbatterisprepared,andanotherreactsatahighertemperature,causingfurtherriseduringbaking.Examplesofhigh-temperatureacidsaltsarealu-miniumsalts,suchascalciumaluminiumphosphate.

Steamisasupplementaryformofleaveninginallproducts.Itisformedwhenwaterischangedtowatervaporasthetemperatureofcakebatterorbreaddoughrises in theoven, thusexertingagreaterpressure inside thecakebatterorbreaddoughandresultinginanincreaseinvolumeofthefinishedproducts.

2.5.1 yeasTeddouGhs

Yeastperformsthreeimportantfunctionsinyeasteddough:leavening,doughrip-ening,andflavordevelopment.Yeastutilizessugartoproducecarbondioxideandethylalcohol.Alongwithethylalcohol,yeastalsoproducesseveralotherorganiccompounds,includingorganicacids,aldehydes,andketones,thatimparttypicalfla-vortotheproduct.

2.5.2 Cakes

Incakemaking,threetypesofleaveningactiontakeplace.Bymechanicalmeans,airisincorporatedduringthecreamingoffatandsugarandthewhippingofeggs.Chemically,airisincorporatedbytheuseofbakingpowderwhichgeneratescarbondioxideduringbakingandbyvaporpressurecreatedbythewater.

2.5.3 BisCuiTs

Biscuits aremainly leavenedbychemicals.Theuseofbakingchemicals suchassodiumbicarbonateandammoniumbicarbonatemakesbiscuitsporousandcrisp.

. funCtIonsofWater

2.6.1 yeasTeddouGhs

Waterisanessentialingredientindoughformulation.Itisnecessaryforsolubilizingother ingredients, for hydrating proteins and carbohydrates, and for the develop-mentofaglutennetwork.Ithasbeenestimatedthatabout46%ofthetotalwaterabsorbedisassociatedwiththestarch,31%withproteins,and23%withthepento-sans(Bushuk,1966).

Wateralsoactsasasolventinthedough,andmanyofthereactionsthattakeplaceduringfermentationcannotoccurifthereisnosolvent.Forexample,wateracts

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asasolventforsomeofthereleasedcarbondioxidegastoformcarbonicacid.Car-bonicacidcontributestotheacidpHofthedoughduringfermentation,providingafeasibleatmospherefortheactionofenzymesandyeastinthedoughsystem.

2.6.2 Cakes

Waterispresentinsufficientquantityincakebatterstodissolvesugar,nonfatdrymilk,salt,andotherdryingredients.Wateraddsmoisturetothefinishedcakesandalsoregulatestheconsistencyofthebatter.Itdevelopstheproteinintheflourtoaverylimitedextentinordertoretainthegasproducedbybakingpowder.

2.6.3 BisCuiTs

Waterhasacomplexroleinbiscuitsbecauseitdeterminestheconformationalstateofbiopolymers,affectsthenatureofinteractionsbetweenthevariousconstituentsoftheformula,andcontributestodoughstructuring(EliassonandLarsson,1993).Itisalsoanessentialfactorintherheologicalbehaviorofflourdoughs(Webbetal.,1970).Bloskma(1971)observedthataddingwatertotheformulareducestheviscosityandincreasesdoughextensibility.Iftheproportionofwateristoolow,thedoughbecomesbrittle,notconsistent,andexhibitsamarked“crust”effectduetorapiddehydrationofthesurface.Anincreaseinwaterresultsintheexpansionofbiscuitslengthwisewithasmallerthickness.

. funCtIonsofsalt

2.7.1 yeasTeddouGhs

Saltisusedforflavorandtaste,notnecessarilyitsown,buttobringoutorenhancetheflavoroftheotheringredientsusedinthedough.Usagelevelsarenormallybetween1.0and2.5%.Saltalso inhibits fermentationdue toosmoticpressureeffect.Yeastcellswillpartiallydehydrateduetotheosmoticpressure.Thefactthatsaltinfluencesthefermentationcanbeusedtocontrolthefermentationrate.Salttoughenstheglu-ten.AccordingtoPreston(1989),saltcauseselectrostaticshieldingofchargedaminoacidsonthesurfaceofglutenproteins,resultinginincreasedinterproteinhydropho-bicandhydrophilicinteraction,whichresultsinanincreaseindoughstrength.

2.7.2 Cakes

Salt isusedasanadjustmentofsweetnessincakes,bringsouttheflavorofotheringredientsincakes,lowersthecaramelizationtemperatureofthebatter,andaidsinobtainingcrustcolor.

2.7.3 BisCuiTs

Salt isusedinallbiscuitrecipesforitsflavorandflavor-enhancingproperties.Itsmosteffectiveconcentrationisaround0.5to1.0%.Saltalsotoughenstheglutenandhencereducesstickiness.

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. funCtIonsofnonfatdryMIlK

2.8.1 yeasTeddouGhs

Nonfat dry milk provides a richer color and a more tempting appearance to thefinished product. It is recommended for use in all sweet dough formulas for theincreasedtolerancesitgivestofermentationandmakeup.Milkishighinlysineandcalcium,andtheoverallqualityofthemilkproteinisexcellent.Milkimprovesthenutritionalqualityof theproduct.MilkhasabuffereffecthencemorestablepH,strengtheningof thegluten if serumproteinhasbeen removedbyheat treatment(Pyler,1988c).

2.8.2 Cakes

Nonfat dry milk in cakes performs the function of structure formation and con-tributestocrustbrowningbecauseofitsproteinandsugarcontent.Milkcontainslactosesugarthatregulatescrustcolor.

2.8.3 BisCuiTsandCookies

Nonfatdrymilkisaminordoughingredientinbiscuitsandcookies,usedtogivesubtleflavorandtexturalimprovementsandtoaidsurfacecoloring.

. funCtIonsofaddItIves

2.9.1 oxidizinGaGenTs

Theuseofoxidizingagentsimprovesthestrengthofsweetdough.Asaresult,theywillimprovedoughhandlingforbettermachiningandcontributetoimprovedgasretention,givingbettervolumeandamoreuniformgrainofthecrumb.AccordingtoCole(1973),oxidantspromotetheformationofdisulfidebondsamongextendedmolecules, therebyimpartinggas-retaininganddough-strengtheningproperties toglutenfilm.Oxidizingagentsarenotbeneficialincakes,cookies,orbiscuits.

2.9.2 reduCinGaGenTs

Theuseofareducingagentreducesdisulfidebondstothesulfhydrylgroup.Theaddi-tionofL-cysteinehydrochlorideandpotassiummetabisulfiteweakensthedough;itnormallyreducesresistancetoextensionandextensographareaandincreasesexten-sibility(MitaandBohlin,1983).Reducingagentsareusefulincertaintypesofbis-cuitdough.Areducingagentsuchassodiummetabisulfiteincreasescookiespreadbydecreasingdoughstability.

2.9.3 surFaCTanTsandemulsiFiers

Inyeasteddoughs,asurfactantformscomplexeswiththeproteinandstarchportionsoftheviscoelasticwheatflourdoughandstrengthenstheextensiblegluten–starchfilmanddelays thesettingof thedoughduringbaking.Theuseofsurfactants in

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yeast-raisedproductsresultsinincreasedproductvolume,amoretendercrustandcrumb,afinerandmoreuniformcellstructurewiththincellwallswhichcausesabrightercrumbcolor,andareductionintherateofcrumbfirmingduetothecomplexformingabilitywithanamylosemoietyofastarchmoleculeandtopreventionofitsleachingoutofthestarchgranuleduringstorage.

Incakebaking,emulsifiersaidtheincorporationandsubdivisionofairintotheliquidphasetopromotefoamformationandalsopromoteuniformdispersionoffatthatcontainsentrappedaircells,therebyprovidingmoresitesfortheexpansionofgas,resultingingreatervolumeandsofttexture(Pyler,1988d).Emulsifiersprovidenecessaryaerationandgasbubblestabilityduringtheprocessuntilthecakestruc-tureisset(SahiandAlava,2003).Emulsifiersalsocoattheexterioroffatparticlessothatthesurfacesoftheparticlesarenolongerdisruptivetotheproteinfilm(Woottonetal.,1967).KimandWalker(1992)reportedthatpolysorbate-60(PS-60)increasedbatterviscositymorethandidsucroseesters.Thismayhavebeencausedbymoreairbubblesbeingincorporatedoramoreair-viscouscontinuousphaseinteractingwithwater.Thevolumeofhigh-ratiocakeandoverallqualityincreasedandcrumbfirmnessdecreasedwithPS-60addition.Jyotsnaetal.(2004)reportedthattheuseofemulsifiergelspreparedusingsodiumstearoyl-2-lactylate(SSL),distilledglyc-erolmonostearate(DGMS),propyleneglycolmonostearate(PGMS),polysorbate-60(PS-60),andsorbitolmonostearate(SMS)incakemakingresultedinadecreaseinbatterdensity,anincreaseinthenumberofevenlydistributedaircellbubbles,andanimprovementinspecificvolumeandtextureofcake.Amongdifferentemulsifiergels,cakeswithPS-60showedamaximumincreaseinspecificvolumefollowedbycakeswithSSL,DGMS,PGMS,andSMSgels.

Considerableinformationisavailableontheeffectofdifferentemulsifiersonthequalityofcookies.Tsenetal.(1975)showedthatemulsifiersimprovedthecookiespreadand,moresignificantly,topgrainscorewhentheywerecreamedintoashort-eningandsugarmixture.Ablendofsurfactantsinsemisweetbiscuitswasshowntohaveseveraladvantages,suchasincreasedmixingtime,greatermixingstability,reducedrateofdoughbreakdown,uniformfatdistribution,preventionofmoisturemigration,andimprovementintexture.Emulsifiersareusedtoreducetheshorteningrequirementsandincreasetheshorteningeffectoffatsbypromotingthetendencyoffattocreamandspreadamongslightlymoistparticlesofsugars,fiber,andotheringredients.Emulsifierstendtomakecookiesdrierandimprovetheirmachinability(KamelandPonte,1993).

SaiManoharandHaridasRao(1999)studiedtheeffectofemulsifiersonrheologicalcharacteristicsofbiscuitdoughandqualityofbiscuits.Theyreportedthattheadditionofanyoftheemulsifiersglycerolmonostearate,lecithin,orsodiumstearoyl-2-lactylateloweredtheelasticvalue,indicatingtheircontributiontotheshorteningeffectonglu-ten,andalsoresultedinareductioninconsistencyandhardnessandmadethedoughmorecohesive.Glycerolmonostearateandlecithinbroughtaboutagreaterimprove-mentinthequalityofthebiscuitwhencomparedwithsodiumstearoyl-2-lactylate.

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2.9.4 enzymes

The functions of enzymes in baked products include flour quality improvement,retardationofstaling,doughimprovement,andmoreefficientmachinability.Fungaland bacterial enzymes available for use in bakery processing includeα-amylase,protease,amyloglucosidases,pentosanase,glucanase,andphytase.Themostimpor-tantoftheseareα-amylaseandprotease.

α-amylaseenzymeisbeneficialinbread,buns,androlls.Supplementationofα-amylaseincreasesfermentablesugars,improvescrustcolor,increasesloafvolume,enhancesflavor,improvesgasretentionthroughstarchmodification,increasesmois-tureretentionofcrumb,andretardsstalingofyeasteddoughproducts.

Supplementationofdoughwithproteaseenzymehelpstobreakdowntheglutenproteinsothatthedoughissofterandmoreextensible(Mathewson,2000).Proteaseenzymeisusedtodecreasethemixingrequirement(inbread),improvethemachin-abilityofadough(insaltinecrackers), increasedoughflowintheoven(cookies),increasepanflow(buns), andcounteract the tendency to springbackwhenpizzadoughisbeingsheeted(Dubois,1980).

2.9.5 viTalwheaTGluTen

Vitalwheatglutenisthenaturalwheatproteinextractedfromflourwhichstillretainsallofitsgluten-formingcharacteristics.Itisaddedtothedoughtostrengthenweakflourandtocarryextraingredientssuchassugars,fibers,andgrains.Vitalwheatglutenisusedinyeasteddoughproductsformulationatlevelsvaryingfrom2to4%basedonflour.Itincreasesthewaterabsorptionofthedoughandimpartsgreatersta-bilitytothedoughduringfermentation.Thesefunctionalpropertiesofvitalglutenareeventuallyreflectedinincreasedloafvolume,improvedgrain,improvedtexture,andsoftnessofcrumb.

2.9.6 hydroColloids

Hydrocolloidsorgumshavebeenwidelyusedinthefoodindustryinordertoimprovefoodtexture,slowtheretrogradationofthestarch,increasemoistureretention,andextendtheshelflife.

The addition of hydrocolloids increases the water absorption capacity of theflour. The highest increase in water absorption was observed by hydroxyl propylmethylcelluloseandalginate(Guardaetal.,2004).Theincreaseinwaterabsorptionisduetothehydroxylgroupinthehydrocolloidstructurewhichallowsmorewaterinteractionthroughhydrogenbonding(Friendetal.,1993).Useofguargumuptoa levelof1%greatlyimprovedtheoverallbread-makingqualityof theflourwithspecialreferencetowaterabsorptioncapacityofthedough,yieldofbread,crumbsoftness,andcrustappearance(VenkateswaraRaoetal.,1985).

Hydrocolloidsmodifythepastingpropertiesof thestarch.Thesestarchprop-erties, including gelatinization temperature, pasteviscosity, and retrogradationofstarch,affectcakebakingandthefinalqualityofcakes(Christiansonetal.,1981;Rojasetal.,1999;Roselletal.,2001).Shelkeetal.(1990)studiedtheeffectsofxan-than,guargum,andcarboxymethylcellulose(CMC)onthequalityofwhitelayer

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cakes.Theadditionofhydrocolloidsincreasedbatterviscosityatambienttempera-tureoverthecontrolvalues,andxanthangavehigherbatterviscositiesthanguarandCMC.Highviscosityduringheatingwouldgivethebattergreatercapacitytoretainexpandingairandnucleiandresistthesettingofstarchgranules,therebyimprovingbothcakevolumeandcrumbgrain.

High-quality cakes have various attributes, including high volume, uniformcrumb structure, tenderness, long shelf life, and tolerance to staling (Gelinas etal.,1999).Theseattributesdependonthebalancedformulas,aerationofcakebat-ters,andstabilityoffluidbattersintheearlystagesofbakingandthethermal-set-tingstage.Then,thequalityofafinishedcakecanbeinfluencedbytheadditionofsubstances(suchashydrocolloids)thataffecttheseproperties.Gomezetal.(2007)studiedthefunctionalityofdifferenthydrocolloids—sodiumalginate,carrageenan,pectin,hydroxy-propyl-methylcellulose(HPMC),locustbeangum,guargum,andxanthangum—onthequalityandshelflifeofyellowlayercakes.Theadditionofhydrocolloidsreducedthequantityofairretainedoncakebatterasdemonstratedbytheincreaseinitsdensity.Cakeswithhydrocolloidshadhighervolumethanthecon-trolexceptwhenalginatewasused.Theyconcludedthattheeffectofhydrocolloidsonyellowlayercakevolumeincreasehastoberelatedtotheincreaseinbattervis-cosityandthechemicalinteractionbetweengumsandstarchthataltersthesettingtemperature.Theoverallqualityoftheyellowlayercakedependednotablyonthetypeofgumadded.ThehighestincreaseintheoverallqualityscorewasobservedwithHPMCfollowedbyxanthanandalginate.Pectinshowedaloweroverallaccep-tancescorethanthecontrol.

.0 reCentstudIesontheeffeCtsof IngredIentsonQualItyofCaKesandBIsCuIts

In response to somepopulation sectorswithparticularnutritionalnecessities, thefoodindustryisbeingchallengedtoredesigntraditionalfoodsforoptimalnutritionalvalueandfortastethatisasgoodasorbetterthanthatoftheoriginal.Onewaytoachieveahealthyfoodproductistoreduceortoomitsomeofthecalorie-contain-ingingredients—especiallysugarandfat—because,atpresent,obesityisfrequentlycitedasaserioushealthproblem(Rondaetal.,2005).Thereareanumberoffatandsugarreplacersinthemarket;however,itisimportanttoconsiderthefunctionalityofthesefatandsugarreplacersinavarietyofhigh-sugar-andhigh-fat-containingprod-uctstoobtainproductswithsimilarqualityparameters(KamelandRasper,1988).

Eggsplayamultifunctionalroleinthecakesystem,affectingfoaming,emulsi-fication,texture,waterbinding,color,andflavor.However,inrecentyears,concernsoverhighcholesterolandhighcostforpeoplewithspecificdietaryneedsorrestric-tions(vegetarians,peoplewithhighcholesterollevels)andfoodsafetyissueshaveled to the replacementofeggs incakes.Theuseofvegetableproteins forpartialortotalsubstitutionofeggsincakeformulationswasreportedbyArozarenaetal.(2001). They suggested the use of white lupine protein, emulsifiers, and xanthangumtoproduceegg-freecake.Studiesbyseveralauthorshavesuggestedtheuseofbovinebloodplasmatosubstituteforeggwhite(Leeetal.,1993)andsoyaflourtosubstituteforegg(GlibertsonandPorter,2001).

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Totakethenextsteptowardcaloriereduction,sugarandfatreplacersareusedinthebakingindustry.Polydextrose,asugarandfatreplacer,isacross-linked,par-tiallymetabolizedglucosepolymer thataddsbodyand texture to reduced-caloriefoods.Itprovides1Kcal/gincomparisonwith4Kcal/gbysucroseand9Kcal/gbyfat.Koceretal.(2007)studiedtheeffectofpolydextroseasasugarandfatreplaceronthequalityofhigh-ratiocake.Theyreportedthatthemajoroutcomeofpolydex-trosesubstitutionwasadecreaseintheaverageporesizeandporesizeuniformityofthecakecrustduetothecombinedeffectofreducedbatterstabilityandinterferencewith thegelatinizationmechanism.Thehigh-ratiocakesystemwithpolydextroseallowed25%fatand22%sugarreplacement,resultingin22%reductionincalorificvaluebasedontotalsugarandfatcontent.

Rondaetal.(2005)studiedtheeffectsofsevenbulkingagents—maltitol,man-nitol,xylitol,sorbitol, isomaltose,oligofructose,andpolydextrose—onthequalityofsugar-freespongecake.Theyobtainedthebestresultswithxylitolandmaltitol,resulting inspongecakesmoresimilar to thecontrol,manufacturedwithsucroseandwiththehighestacceptancelevelinsensoryevaluations.Theyalsoconcludedthatmannitolproved tobe theworst substituteof sucrose amongall thebulkingagentstested.

Gallagheretal.(2003a)studiedtheevaluationofraftilose,anoligosaccharidesuccessfullyusedinfoodproductsasasugarreplacerinshortdoughbiscuitproduc-tion,wherethesugarwasreplacedby20to30%.Theyreportedthatatthelowerandmedium levelsof sugar replacement, raftilosecanbeused successfully to reducesugarinshortdoughbiscuits.

Gallagheretal.(2003b)developedaformulationforabiscuitcontainingreducedfat and sugar levels as well as exhibiting functional properties using Novelose®,sodiumcaseinate,Raftilose®,andSimplesse®.Theyopinedthatacombinationoftheabovefourfunctionalingredientsproducedabiscuitofextremelyhighstandards.

. ConClusIon

Ingredientsplayamajorroleinthedevelopmentofaproduct.Sugarconferssweet-ness,fatlubricatesdoughandshortensthecontinuityofgluten,waterisnecessaryforhydratingproteins,carbohydratesarenecessaryforthedevelopmentoftheglutennetworkandthesolubilizingofotheringredients,nonfatdrymilkprovidesarichercolorandamoretemptingappearancetothefinishedproduct,leaveningagentsaer-atethedoughorbatterandcontributelightnesstotheproduct,andadditivesbringaboutimprovementsinthemachinabilityofthedoughandthequalitycharacteris-ticsofproducts.Replacersoffat,sugar,andeggareusedinthebakeryindustrytoimprovethenutritionalstatusofbiscuitsandcakes.Manyofthefunctionsofingre-dientsdescribedinthischapterwillbeusefulforabakingtechnologistindevelop-ingnovelformulationsforsweetgoods,understandingtheroleofingredientsinthebuildingupoftheproduct,counteractingtheproblemsthatmayariseduringpro-cessing,improvingtheproductquality,maintainingtheconsistencyinthequalityoftheproduct,andhandlingbulkproductionsconfidently.

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Bean,M.M.,W.T.Yamazaki,andD.H.Donelson.1978.Wheatstarchgelatinizationinsugarsolution. II. Fructose, glucose and sucrose: Cake performance. Cereal Chemistry55:945–952.

Bean, M.M. and C.S. Setser. 1992. Polysaccharide sugars and sweeteners. In: Bowers, J.(Ed.).Food Theory and Applications,pp.69–198.Macmillan,NewYork.

Bloskma, A.H. 1971. Rheology and chemistry of dough. In: Pomeranz, Y. (Ed.). Wheat Chemistry and Technology, 2nd ed., pp. 558–560. American Association of CerealChemistry,St.Paul,MN.

Brooker,B.E.1993a.Thestabilizationofairincakebatters—Theroleoffat.Food Structure12:285–296.

Brooker,B.E.1993b.Thestabilizationofairinfoodscontainingfat—Areview.Food Struc-ture12:115–122.

Bushuk,W.1966.Distributionofwaterindoughandbread.Baker’s Digest40:38–40.Christianson,D.D.,J.E.Hodge,D.Osborne,andR.W.Detroy.1981.Gelatinizationofwheat-

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3 Chemical Reactions in the Processing of Soft Wheat Products

Hamit Köksel, Vural Gökmen

Contents

3.1 Introduction................................................................................................... 493.2 LeaveningSystems:ChemicalLeaveningversusYeastLeavening..............50

3.2.1 GasesActingintheLeaveningofBakeryProducts.......................... 513.2.2 ChemicalLeavening.......................................................................... 51

3.2.2.1 AmmoniumBicarbonate...................................................... 523.2.2.2 SodiumBicarbonate............................................................. 523.2.2.3 PotassiumBicarbonate.........................................................543.2.2.4 SodiumCarbonate................................................................54

3.2.3 BakingPowders.................................................................................543.2.3.1 Single-ActingandDouble-ActingBakingPowders.............563.2.3.2 LeaveningAcids...................................................................563.2.3.3 DoughReactionRateandBatterReactionRate.................. 613.2.3.4 NutritionalValuesofBakingPowders................................. 613.2.3.5 UtilizationofBlendsofChemicalLeaveningAgents

andPremixes........................................................................ 623.2.3.6 EffectofBatterViscosityandCO2ProductionRateon

theQualityofSoftWheatProducts..................................... 633.3 MaillardReaction.........................................................................................65

3.3.1 FormationofColor.............................................................................663.3.2 FormationofFlavorandAromaCompounds.................................... 673.3.3 FormationofAntioxidants.................................................................683.3.4 LossofNutritionalQuality................................................................693.3.5 FormationofToxicCompounds........................................................69

3.3.5.1 Acrylamide...........................................................................693.3.5.2 Hydroxymethylfurfural(HMF)........................................... 73

References................................................................................................................ 76

. IntroduCtIon

Foodchemistrytracesthecontinuousseriesofchemicalreactionsinthechemicalsystemthatwecall“food” throughvariousstagessuchasharvesting,processing,storage,andconsumption.Abroadrangeofreactionsoccurparticularlyduringfood

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processing.Thesechemicalreactionstakeplaceinlipids,proteins,carbohydrates,andotherfoodconstituentswhichprimarilyinvolveoxidation,degradation,dena-turation,aggregation,hydrolysis,andpolymerization.Theyhavekeyimportanceinproducingdesirableandundesirablechangesinfoodproductsandmustbeunder-stoodfromthelegalandtoxicologicalpointsofview.Agoodunderstandingofthechemistryofafood-processingsystemisexpectedtohavesignificantcontributionstothesuccessfulcontroloftheprocessaswellasthequalityofthefinalfoodproduct.

Thebakingqualityof softwheatproductsdependson the interactionsof thevariouschemicalsinflourandtheothersubstancesusedintherecipe.Batteranddough systems, used in theproductionof softwheat products, serve as chemicalreaction pools with their wealthy composition. The wide range of ingredients inthemaffectsthepHandresultsincharacteristicflavorsandcolors,oftendesirablebut sometimesundesirable.Baking results invarious typesofchemical reactionsandphysicalchangesduetosimultaneousheatandmasstransfer.Thefirststageofbakingischaracterizedbyaphysicalchangeindoughstructurefrom“moist-soft”to“dry-hard.”Evaporativecoolingpreventsthetemperatureofdoughfromexceeding100°Cinearlystages.Hence,thetypesandprogressionsofchemicalreactionsaredifferentindifferentstagesofbaking.Itshouldberealizedthatanunderstandingofthechemistryofanyfood-processingsystemisnecessarytoattainsuccessfulcontroloftheprocess.Therefore,thedevelopmentofawell-controlledmanufacturingpro-cessofsoftwheatproductsmakesitnecessaryforthefoodengineerortechnologisttounderstandthemainreactionsinchemical leavening(i.e.,foamgenerationandbatteranddoughstabilization),nonenzymaticbrowning,andvariousotherreactionsthataffectdifferentpropertiesofsoftwheatproducts,suchasstructure,texture,fla-vor,taste,andcolor.Manyofthesereactionsinitiatedbyprocessingaremediatedbyfreeradicalsandinvolvesite-specificreactionsthatleadtofunctionalornutritionalchangesinfoods.However,thischapterisnotintendedtocoverallofthechemicalreactionsthatoccurduringtheprocessingofsoftwheatproducts.Themainaimwastocoverchemicalleaveningreactionsandnonenzymaticbrowningreactions.

. leavenIngsysteMs:CheMICal leavenIngversusyeastleavenIng

Gasmustbegeneratedwithinthebatterordoughduringmixingandtheearlystagesofbakinginordertoobtainalight-texturedproductwithacharacteristicporouscel-lularstructure.Theproductwillhavealargenumberofgascellsanddesiredeatingcharacteristicswithsuitableleaveningaction.Theprocessstartswiththeincorpo-rationofair(orothergases)intothebatterofdoughtoformanucleusofgascells.Thesegascellswillexpandwiththeeffectoftheleaveningsystemandalsoduringbakingtocreatethestructureofthefinalproduct(Hoseneyetal.,1988).

Mainly,twotypesofleaveningsystemsareusedinbakedgoods:yeastleaven-ing and chemical leavening. Anaerobic fermentation of sugars by yeast producesCO2andethanol.Carbondioxideproducedbyyeastisthemajorleavenerforbread.Water–ethanolazeotrope,whichhasaboilingtemperatureof78°C,mightalsocon-tribute to the expansionof yeast-leavened products. It vaporizes and expands thedoughwhileitisheatedintheoven(Hoseneyetal.,1988).

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Chemical Reactions in the Processing of Soft Wheat Products

Yeast leaveningiswidelyusedinbread-typeproductsbut ishardlyeverusedinsoftwheatproductsduetoitsundesirableinfluenceondoughrheologyandthetextureofthefinalproduct.Peoplealsopreferchemicalleaveningtoyeastleaveningduetoacoupleofotherreasons.Yeastgenerallyrequires2to3hoffermentationtoproduceCO2bubbles,andtheactionofchemicalleaveningagentsisalmostinstan-taneous.Chemicallyleavenedcookiescanbeeaten15minaftermixingabatchofdough.Thedoughsusedinsoftwheatproductsareusuallyrichinfatandsugarbutusually lowinwatercontent.Theirsugarcontentmightexceed50%(flourbasis).Therefore,yeastisnotsuitableasaleavenerinmostofthesoftwheatproducts.

3.2.1 GasesaCTinGinTheleaveninGoFBakeryProduCTs

Variousgasesareusedfortheleaveningofbakedgoods.Themainonesareair,carbondioxide,waterandethanolvapor,andammonia.Airisamixtureofgases(nitrogen78%,carbondioxide0.03%,oxygen21%,othergases<0.1%).Itispresentinallbakedproductsandhassomeleaveningaction.Amongthesegases,carbondioxideandoxygendonotcontributemuchtotheformationofbubblesinabatteror dough because they are quite soluble in water. In contrast, nitrogen, the mainconstituentofair,isnotverysolubleinwaterandisincorporatedintodoughorbat-terduringmixingtocreatebubbles.Waterisalsopresentinthebatteranddoughofallbakedproducts.Evaporationofwaterinabatterordoughaffectstheexpansionprocesstosomeextent.Theexpansionofgascellsbywaterdependsontheexcessvaporpressureintheproductduringbaking.Thus,thetemperatureinsidethebatterordoughisimportantbecausewatervaporpressurewillincreasegraduallyastem-peratureincreasestowardtheboilingpointofwater.However,theleaveningeffectofwaterisratherlowduetoitsrelativelyhighboilingpoint.Itmayserveasanefficientleaveneronlyifthebatterordoughsystemisheatedveryrapidly(e.g.,wafers).

3.2.2 ChemiCalleaveninG

ChemicalleaveningsystemsproduceCO2byeitherchemicaldecompositionthroughtheapplicationofheatorareactionofanacidiccompoundwithabase.Gascanformduringallphasesoftheprocessing(e.g.,mixing,forming,andbaking).Thepointatwhichgas formationoccurs is controlled largelyby the compounds used.Thecompositionoftheleaveningsystemaswellastherateandstageatwhichthegasisreleasedinfluencethequality(appearance,texture,color,andeventheflavor)ofthefinalproduct(CauvainandYoung,2006).

Chemicalleaveningprovidesahighlevelofcontrolofthereactionatthedesir-ablestage(duringthemixing,atthebench,orintheoven).Themajordevelopmentareainchemicalleaveninghasbeenhowtocontrolthereactionanditsspeed.Com-monsourcesofcarbondioxidearesodiumandammoniumbicarbonates.Althoughcarbonatesarealsopotentialsourcesofcarbondioxide,theyarenotcommonlyusedduetotheirhighalkalinity(Hoseneyetal.,1988).

Carbondioxidecanexisteitheringaseousform(asfreeCO2)orintwodifferentionic forms (bicarbonate: HCO3

−1 or carbonate: CO3−2). Their relative proportion

dependsonthepHandtemperatureofthesystem.Thegaseousform(CO2)ispre-dominantatverylowpHvalues,andthecarbonateionispredominantatveryhigh

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pHvalues.IfthepHisabove8.0,noleaveninggas(CO2)willbeavailable.ThepHvaluesofmostofthesoftwheatproductsarearound7.0,andonlypartofthecarbondioxideisintheleaveninggasform(CO2).Becausesodiumbicarbonateisalkaline,thepHofthebatterordoughincreasestoavalueatwhichnoleaveninggas(CO2)isreleased.Thebatterordoughmustincludeanacidtoreleasesignificantamountsofgas.Someoftheingredientsusedinsoftwheatproductsareacidic(e.g.,acidicfruits,buttermilk).Therequiredacidityisusuallyprovidedusingtheseingredientsinhomebaking.However,incommercialapplicationsofchemicalleaveningsystems,acidsoracidiccompoundsareaddedtoprovideconsistentandcontrolledgasproduction(CauvainandYoung,2006;Hoseney,1994).

... ammoniumBicarbonate

Ammoniumbicarbonate(ABC),ammoniumsaltofcarbonicacid,decomposescom-pletelyintoammonia,carbondioxide,andwaterwhenheatedtoabove40°C.

NH HCO NH CO H O4 3 3 2 2→ + +

Itisalsocalled“volatilesalt”(sal volatileor“Vol”inshortform)becauseofthiscompletedissociation.

Onecaneasily smell thepungentodor escaping from thedoughandproductduringprocessing.Thepungentodorisduetoammoniagas(NH3)thatcombineseasilywithwatertoformammoniumhydroxide(NH4OH).Afterthedecomposition,thereisnoresidualsalt.Thisisadvantageousbecauseresidualsaltsmightinfluencethedough rheologyand the tasteof thefinalproduct.Products includingammo-nium bicarbonate as a chemical leavener must be baked thoroughly. Ammoniumbicarbonatedissipates in low-moistureproducts, suchascookiesandcrackers. Inhigher-moistureproducts,ontheotherhand,waterretainstheammoniaandammo-niumhydroxideisformed(especially in themoistcrumbofbakedgoods),givingtheproductanundesirableflavorandodor.Thecrumbtakesonagreenishcolorandproducesanalkalinetaste.

Somegasisreleasedfromammoniumbicarbonateatroomtemperatureduringmixingandforming,butmostisgeneratedduringbaking.Thedissociationisfasterduringbakingasthetemperaturesreachtoaround60°Candabove.Acidiccondi-tionsacceleratethereactionatlowertemperatures.Therapidreleaseofgasresultsinrelativelylargecells.Ammoniumbicarbonatenotonlyincreasesthevolumeorheight,butalsoislikelytoincreasethespreadincookies.

Ammoniumbicarbonate ismarketedasawhitecrystallinepowder thathasatendencytolumping.Therefore,itisnotsuitableforstorageevenatdryconditions.Itisbettertodissolveammoniumbicarbonateinwaterbeforeusingtoavoidproblemsthatmightbecausedduetoseverelumping.

... sodiumBicarbonate

Sodiumbicarbonate(bakingsoda;NaHCO3)isthemostpopularleaveningagent.Itisawhitecrystallinealkalinecompoundthatreactsbyeffervescing(fizzing)when

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itcomesintocontactwithacids,thusproducingcarbondioxide.Thischemicalreac-tion facilitates the rising action inbakedgoods.There arevarious advantagesofsodiumbicarbonate(Hoseneyetal.,1988;Hoseney,1994):

Commercialbakingsodaisrelativelyinexpensive,anditisreadilyobtain-ableathighpurityandvarioussizegrades.Itisstableduringstorageandeasytohandle.Itdoesnotaffectthetasteofthefinalproducttoalargeextent.Itisnontoxic.

Whenwaterandacidiccompoundsarenotavailable,sodiumbicarbonatewillreleasesomeofitsCO2andwillbeconvertedintosodiumcarbonateuponheating.Thisoccursathightemperatures(≥90°C)andcannotbeusedforchemicalleaven-ing.Itcanberepresentedbythefollowingequation:

2 3 2 3 2 2NaHCO Na CO CO H Oheat → + +

WhenanaqueoussolutionofNaHCO3isheated,justafractionofCO2willbereleased.Ifthissolutioniscooled,complexsaltcrystals(Na2CO3⋅ 2NaHCO3⋅ 2H2O)containingonepartNa2CO3andtwopartsNaHCO3willbeformedwhichcanberepresentedasfollows:

4 23 2 3 3 2 2NaHCO heat Na CO NaHCO CO H O → + +.

Ontheotherhand,ifwaterandacidiccompoundsareavailable,sodiumbicarbonatewillreactwithacidiccompoundstoliberateCO2anddecomposetogivewaterandthesodiumsaltoftheacidiccompound:

NaHCO H Na CO H O3 2 2+ → + ++ +

ThisreactionismoredesirablebecausereactionwithanacidconvertsallofthesodiumbicarbonatetoCO2andwater,whilethefirsttworeactionsconvertsodiumbicarbonatetosodiumcarbonate,CO2,andwater.Sodiumcarbonateresidueisnotdesirableinthefinalproductduetoitsbitterandsoapytaste(Hoseney,1994).

TheCO2releasedisusuallyrequiredasaraisingagentandanearlyreactionisnotdesirable.Therefore,sodiumbicarbonateshouldbekeptawayfromotheringre-dientsaslongaspossible.Forexample,sodiumbicarbonateisaddedatthelaststageofmultistagemixingprocedures.Ifsodiumbicarbonateisaddedatthelaststage,itmustbesievedtoevenlydistributeitintothedoughorbattersystemandtoeliminatelumps.

Therearevariousparticlesizegradesofsodiumbicarbonatesuitableforbakeryproducts.Useofthecoarsergradescanreducethetendencyofsodiumbicarbonatewithacidforprereactionandincreasethesystem’sstability.However,sodiumbicar-

•

•••

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bonatewithcoarsergranulationmaynotdissolvequicklyduringthepreparationofthebatterordoughandmaycausedarkerspecksonthesurfaceofcookies.Anexcessiveamountofsodiumbicarbonatewillresult incookieswithanalkalinecharacteristicandyellowishcrumbandcrustcoloration.Thisisaccompaniedbyanunpleasanttaste(knownassoda-bite).Ifthelevelofsodaisexcessive,highpHvaluesmayalsocausesoapyflavorsproducedbyreactionwiththefatsinformula.Ifthelevelistoolow,itwillallowtheacidicflavorstocomethrough.Therefore,itisusuallyaimedtoachieveapHvalueofaround7.0±0.5 incookiesby theuseofanappropriateamountofsodiumbicarbonate(CauvainandYoung,2006;Manley,1991).However,afewspecialtypesofproductsdeflectfromthispHvalue(sodacrackersarealkaline,cheesecrack-ersareacidic).Sodiumbicarbonatecanbeencapsulatedbyusingfat-basedcoatingstoincreaseitsstability,particularlyforrefrigerateddoughs.Theencapsulatedformsarequitesuccessfulbutcostly,sotheyareusuallyusedinvalue-addedproducts.

... PotassiumBicarbonate

Potassiumbicarbonate(KHCO3)isapotentialsourceofcarbondioxide,especiallyinreduced-sodiumproducts.Becauseithasagreatermolecularweightthansodiumbicarbonate,itrequiresapproximately20%morefortheequivalentleaveningaction(forneutralizationoftheacidsusedintheformula).PotassiumbicarbonateresultsinahighercrumbpHthansodiumbicarbonateandmaycontributeasharpaftertastetoproducts.Itishygroscopic.Itisnotcommonlyusedbecauseithasatendencytoimpartslightbitternesstotheproducts.Thereactionofpotassiumbicarbonatewithacidissimilartothatofsodiumbicarbonate:

KHCO H K CO H O3 2 2+ → + ++ +

... sodiumCarbonate

Sodiumcarbonate(Na2CO3) isalsoapotentialsourceofcarbondioxide.It isnotusedduetoitshighalkalinity,whichincreasestheriskofgettingalocalizedregionofveryhighpHindough.SuchhighpHregionsmightbedetrimentaltothequalitycharacteristicsofthefinalproduct.

3.2.3 BakinGPowders

Anumberofleaveningacids(oracidsalts)canbeincorporatedintotheleaveningsystemtoobtainalargeryieldofgasandtocontroltherateofCO2release.Bakingpowdersconsistofmixturesofsodiumbicarbonate,oneormoreacidiccompounds(acidicsaltsoracids),andaninertdiluentsuchasstarchorcornflour.Thediluentphysicallyseparatestheacidandbaseandpreventstheirearlyreactionduringstor-ageofthebakingpowder.Thesaltdissociatestogiveanacidicreactioninsolutionatdifferentstagesofprocessing.Thepurposeofpreparingsuchamixtureofchemi-calsistoproduceCO2bubblesduringmixing(atroomtemperature)orasthedoughorbatterisheatedintheoven.Creamoftartar,calciumphosphate,andcitrateare

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commonlow-temperatureacidsalts.High-temperatureacidsaltsareusuallyalumi-numsalts,suchascalciumaluminumphosphate.Theycanbefoundinmanybak-ingpowders.Althoughdietaryaluminumisnotdefinitelyknowntobeharmfultohumanhealth,bakingpowdersareavailablewithoutaluminumsaltsforpeoplewhoareafraidofconsumingaluminum,andalsoforthosesensitivetothetaste(Conn,1981;Hoseney,1994).

Strongacidssuchassulfuricacidorhydrochloricaciddissociatecompletelyandgivehighlevelsofhydrogenioninsolution.Theyreactveryrapidlywithsodiumbicarbonate. On the other hand, weak acids such as tartaric acid and lactic aciddissociateincompletelyandgeneratelowerlevelsofhydrogenionascomparedtostrongacids.Asaconsequence,theyreactslowlywithsodiumbicarbonate.Otheracidiccompounds,suchaspartiallyneutralizedacids,haveanintermediateposition.Neutral salts suchas sodiumaluminumsulfatecan functionasacids through thehydrolysisreactionthatcreateshydroxidesandhydrogenions:

NaAl SO H O Al OH Na SO H( ) ( ) ( )4 2 2 3 423 2 3

3

+ → + + ++ − +

HH NaHCO Na CO H O+ ++ → + +3 3 3 33 2 2

Theamountof acidneeded in a formulation isdeterminedby theamountofsodiumbicarbonateandtheneutralizingvalueofacidoracidsaltusedinthefor-mula.Becausetheacidityisusuallyprovidedbyacidicsalts,insomecases,stoichi-ometryofthereactionisnotclear.Therefore,theconceptofneutralizingvalue(NV)wasintroducedinordertodeterminetheamountofacidneededinaformulation,tocomparetheCO2-releasingpowerofvariousleaveners,andtoallowthecorrectlevelofusage.NVisameasureoftheacidrequiredwithinaspecificbakeryformulation(Conn,1981;Hoseney,1994).

Theneutralizingvalueofaleaveningacidistheamount(g)ofsodiumbicarbon-ateneededtocompletelyneutralize100gofthatacid(Equation3.1).TheneutralizingvaluesofvariousleaveningagentsarepresentedinTable3.1(Conn,1981;Thacker,1997).Inmostapplications, thegoal is tohavelittleornosodiumbicarbonateorleaveningacidremaininginthefinishedproduct.However,sometimesanadditionalamountofsodiumbicarbonateoracidisusedtoprovideaspecificpH-relatedeffect,suchascolororflavormodificationoradjustment.

Neutralization value g of NaHCO

g acidic3=

100 ssalt×100

(3.1)

OtheringredientsincludedintheformulationalsoaffectthepHofaproduct,sotheadditionofleaveningacidsandbasesinneutralproportionsdoesnotassureaneutral pH in thefinalproduct.Changing thepHmay influence the speed andreactivityoftheleaveningsystem.Thedegreeofflourbleachingandaddingingre-dientslikeacidicfruits,buttermilk,cocoapowder,orhigh-fructosecornsyrupcansignificantlyalterthepHofthefinalproductandaffectitsvolume.Manyingredientscontainorganicacidsthatwillreactrapidlywiththesodiumbicarbonate.Therefore,

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itisimportanttomakesureifthepHofthebatterordoughiscorrectafterformula-tion.ItmaybenecessarytoregulatethepHtogettherightresultinthefinalproduct(Hoseney,1994).

... single-actinganddouble-actingBakingPowders

Baking powders might be either single acting or double acting. Combinations ofacidscanbeusedtocreatedouble-actingbakingpowders.Inthistypeofleaveningsystem,oneacidreactsatroomtemperature,usuallyreleasingasmallamountofgas,andanotheracidreactswhenbatterordoughisheatedintheoven,releasingtherestofthegas.Theinitialgasrelease(duringmixing)providessmallgascells(nucle-ation)thatpromotehomogeneousexpansionoftheproductduringbaking.Thisgascellnucleationcanalsooccurby incorporatingairduringmixing.Thebetter thedispersionofthesenucleatinggascells,thefinerthegraininthefinalproduct.Dur-ingbaking,therateatwhichCO2isformedandthecontinuityofCO2productionarebothimportant.IfanexcessiveamountofCO2isproducedatthebeginningandthereactionfinishes,thecakewillcollapsewhenitistakenfromtheoven.There-fore,somebakingpowdershavetwodifferentacidstoguaranteefastinitialreactionand continuity of the CO2 production during baking (Cauvain and Young, 2006;Hoseney,1994).

... leaveningacids

Theoriginalleaveningacidsforbakingwerethelacticacidinsouredmilkandcreamoftartar.Thetechnologicaldevelopmentsledtotheutilizationofothercompoundsthatarelessexpensiveorlessreactive.Hence,CO2isreleasedwhentheproductis

taBle.

neutralizingvaluesofleaveningagentsleaveningacids reactionrate neutralizingvaluea

Monocalciumphosphate Veryfast 80

Sodiumaluminumphosphate Slow 100

Sodiumaluminumsulfate Medium 100

Glucono-δ-lactone Continuous 45

Sodiumacidpyrophosphate Medium 72

Dicalciumphosphatedihydrate Slow 33

Creamoftartar Veryfast 45

Calciumacidpyrophosphate Medium 67

Adipicacid Veryfast 115

Fumaricacid Medium 145

Citricacid Veryfast 159a Gramsofsodiumbicarbonateneededtoneutralize100gofleaveningacid.

Source:FromConn,J.F.,Cereal Foods World,26,119–123,1981;Thacker,D.,inThe Technology of Cake Making,6thed.,Chapman&Hall,London;NewYork,1997,100–106.

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placedintheovenratherthanduringmixing.Severalcommercialproductsareusedasleaveningacids.Theyvaryinneutralizingvalue,reactionrateatvarioustempera-tures,andeffectonthefinishedproduct(Table3.1).

3.2.3.2.1 Creamoftartar (KHC4H4O6; Monopotassium Salt of Tartaric Acid, Potassium Acid Tartrate, or Potassium Bitartrate)

H C C

C

C

C

C

O

O O

O

O O

H

H

H

H

H

HH

H

C

C

C

C

OH

OH

OH

OH OH

OHOHOH

OH

OH

OHOH

OH

HOHO

HOHO

CH2OH

CH2OH

HOOC—CH—CH—COO_

K+

CH2OH

CH2OH

D-Glucose α-D-Glucopyranose D-Glucono-1,5-lactone D-Gluconate

1/2O2 H2O2

Cream of tartarCreamoftartarhastraditionallybeenusedinbakingapplications,butitsusein

commercialapplicationsislimitedduetoitshighcostandveryfastreactionrate.Itisobtainedasaby-productofwineproduction.Itreactsquicklyatroomtemperature.

KHC H O NaHCO KNaC H O CO H O4 4 6 3 4 4 6 2 2+ → + +

Cream of Sodium Potassium tarter bicarbonate sodium tartrate

Inreduced-temperaturebatters,creamoftartarhaslimitedsolubilityresultinginlimitedgasdevelopmentduringtheinitialstagesofmixingatlowertemperatures.Therateofreactionincreasesathighertemperatures(roomtemperatureandabove).Becauseofthesecharacteristics,anditspleasanttaste,creamoftartarisusedinsomebakingpowdersandintheleaveningsystemsofanumberofbakedgoodsanddrymixes.

3.2.3.2.2 tartaricacid (H2C4H4O6)

C

C

C

C

C

C

C

C

C

O

O

O

OH H H

H

H

H H

H

H

H

H

HO HO HOH

OH

OH OH OH

OH

OH

OH

CH2OH CH2OHCH2OH

α

β

γ

δ

ε

α

β

γ

δ

ε

+ H2O + H2O

H2O,

COOH C

C

C

C

C

D-Glucono-1,5-lactone(delta lactone)

D-Gluconic acid D-Glucono-1,4-lactone(gamma lactone)

OH OH

HOOC—CH—CH—COOH

52748.indb 57 2/6/08 2:25:02 PM



Tartaric acidTartaricacidissolubleinbothcoldandhotwater.Incoldwater,itreactswith

sodiumbicarbonateinstantly.Thesaltremainingafterthereaction(sodiumtartrate)hasalaxativeeffect.Hence,somepeopledonotchoosetouseitinbakingapplica-tions.However,thequantitiesusedinbakingareverysmallandshouldnothaveasignificantlaxativeeffect.

H C H O NaHCO Na C H O CO H O2 4 4 6 3 2 4 4 6 2 22 2+ → + +

Tartaric Sodium Sodium acid bicarbonate tartrate

3.2.3.2.3 MonocalciumPhosphate (MCP)MCPalsoreactsquicklyatroomtemperaturewiththesodiumbicarbonatewhendis-solved,releasingapproximatelytwothirdsoftheCO2inthefirst2min:

3 8 4 82 4 2 3 3 4 2 2 4Ca H PO NaHCO Ca PO Na HPO C( ) ( )+ → + + OO H O2 2+

Hence,MCPoftenactsasanucleatingacid.Itisoftencombinedwithaslower-actingacidinproductsrequiringadouble-actingleavener,suchaspancakebatter.Itisalsocalledcalcium biphosphateoracid calcium phosphate(ACP),andthecom-mercialproductisusuallyinthemonohydrateform,monocalciumorthophosphatemonohydrate,withthechemicalformulaCa(H2PO4)2⋅H2O.ItisnecessarytouseafinelypowderedformofACPtoeliminatetheriskofblackspeckformationonthesurfaceoftheendproduct.

The monohydrate form of ACP reacts as fast as cream of tartar, but the saltobtainedbydryingthemonohydrateform(anhydroussalt)reactsatonlyabout80%ofthisrate.Coatedanhydrousmonocalciumphosphatemaybeusedinapplicationswheretheinitialgasreleasemustbeslowed.Theinitialreactionreleasesabout20%oftheCO2,withapproximately50%releasedafter10to15min.Thistypeofproductisusedincakemixesandself-risingflourorcornmeal.

3.2.3.2.4 sodiumaluminumsulfate(SAS)SASwasusedasthesecondacidindouble-actingbakingpowdersincombinationwithMCP.Itreactstooslowlytobeusedextensivelyincommercialapplications,althoughsometimesitisusedinformulationssuchasretailcakemixes.Themaindisadvantages of SAS are its slight astringent taste and its weakening effect oncrumbtexture:

NaAl SO NaHCO Al OH Na SO CO( ) ( )4 2 3 3 2 4 23 2 3+ → + +

3.2.3.2.5 sodiumacidPyrophosphate (SAPP; Na2H2P2O7 ⋅ H2O)SAPPhasaslowrateofreaction,especiallyundercoldconditions.ItreleasesmostoftheCO2duringbaking:

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Na H P O NaHCO Na P O H Oheat

2 2 2 7 3 2 2 7 22 2 2 + → + + CCO2

Sodium Sodium Sodium pyrophosphate bicarbonate phosphate

ThereareseveraltypesofSAPPs.Theyshowvariousratesofreaction,depend-ingonhow theyaremade.Theydiffer in termsofprocessingconditions,poros-ity,andgranulation,buttheyarechemicallythesame(Na2H2P2O7).SAPPtypicallyreleases20to40%oftheCO2gasinthefirst2minofmixing,littleornoneduringholding, and the rest duringbaking.High levelsofSAPPcan result in a slightlybitteraftertaste(pyrotaste)inthefinishedproduct.Thepyrotastedoesnotcomefrompyrophosphates.Thepyrophosphatesarebrokendowntosodiumphosphatebyenzymesinthedough.Itappearsthattheaftertasteisduetotheexchangeofcalciumwiththesodiumfromthesurfaceoftheteeth.Theproblemhasbeenpartiallysolvedbyaddingvariousformsofcalcium(e.g.,calciumlactate)tothebakingpowderinsmallamounts.SAPPsmightalsocauseascratchysensationatthebackofthethroatandapepperyaftertaste,whichisnoticeableinproductswithlowersugarcontentandmaybemaskedbyhighlevelsofsweetness.SAPPsareoftenusedinrefrigeratedandfrozendoughandcakedoughnuts.

3.2.3.2.6 sodiumaluminumPhosphate (NaH14Al3(PO4)8 . 4H2O, Sodium Acid Aluminum Phosphate, SALP)SALPisaneutralsalt.Ithashighneutralizingvalue(Table3.1)andiseconomicaltouse.TheproductionofacidfromSALPcanberepresentedbythefollowing:

NaH Al PO H O H O Al OH Na H14 3 4 8 2 2 34 5 3 4( ) . ( )+ + +→ +22 4 4

24 11PO HPO H− − ++ +

SALPreactsslowlyanddoesnotresultinoff-flavorsoraftertasteinthefinishedproduct.Itissuitableforuseindoughsorbattersthatmightstandforlongperiodsbeforebaking.SALPiscommonlyusedasthesecondacidindouble-actingbakingpowders.It isusedinplaceofSAPPinproducts likecakeandmuffinmixesandgiveswhitercrumbthanSAPP.SALPhasatenderizingeffectonbakedproducts.Itinitiallyreleasesabout20%ofthecarbondioxide,withtherestgeneratedduringbaking.

SALPismostcommonlyusedforproducing“self-raising”flourduetoitsgreaterresistancetoreactingwithsodiumbicarbonatewhenmixedinflourthatusuallyhas14%(orlower)moisturecontent.

3.2.3.2.7 dicalciumPhosphatedihydrate (DPD; CaHPO4 ⋅ 2H2O)Dicalciumphosphateisneverusedbyitselfasaleaveningacid,butitcanbeusedincombinationwithotherleaveningacidstoreleaseCO2laterinbaking,usuallyafter20minbakingtime.Itiscommonlyusedindehydratedform,anditisnotanacidicsalt.However,athigher temperatures,DPDdisproportionatesandgivesanacidicreaction,resultinginaleaveningeffect.Itisusedinspecialbakingapplicationsthatrequireveryslowgasrelease.Ithasnoactivityduringmixingoronthebench,and

52748.indb 59 2/6/08 2:25:05 PM



itreactsonlywhenthetemperatureexceeds57°C.Thismeansthatitcanbeusedonlyinproductsthathaveextendedbakingtimes.ItisusefulforadjustingthepHofthefinalproduct.

3.2.3.2.8 glucono-δ-lactone (GDL; C6O6H10)Glucono-δ-lactone is an intramolecular ester of gluconic acid. Glucose oxidaseenzymeoxidizesD-glucoseintoD-glucono-δ-lactone.

H C C

C

C

C

C

O

O O

O

O O

H

H

H

H

H

HH

H

C

C

C

C

OH

OH

OH

OHOHOH

OH

OH

OHOH

OH

HOHO

HOHO

CH2OH

CH2OH CH2OH

CH2OH

D-Glucose α-D-Glucopyranose D-Glucono-1,5-lactone D-Gluconate

1/2O2 H2O2

ItisproducedcommerciallybyfermentationinvolvingAspergillus nigerorA. sub-oxydans.Althoughitisnotanacid,inaqueoussolutionitslowlyhydrolyzestoanequilibriummixtureofgluconicacidanditsδ-andγ-lactones.Atroomtemperature,thishydrolysisreactiontakesaround2handyieldsabout60%gluconicacid.Thehydrolysisrateincreasesathighertemperatures.

C

C

C

C

C

C

C

C

C

O

O

O

OH H H

H

H

H H

H

H

H

H

HO HO HOH

OH

OH OH OH

OH

OH

OH

CH2OH CH2OHCH2OH

α

β

γ

δ

ε

α

β

γ

δ

ε

+ H2O + H2O

H2O,

COOH C

C

C

C

C

D-Glucono-1,5-lactone(delta lactone)

D-Gluconic acid D-Glucono-1,4-lactone(gamma lactone)

Ithasaslowbutcontinualreactionrate.Themaingasreleaseoccursduringbak-ingastheingredientisslowlyhydrolyzed.Italsohasanadvantageinthatthereisnoaftertaste.AlthoughGDLisrelativelyexpensive,therearecertainspecializedtypesofproductssuchaspizzadough,cakedoughnuts,andrefrigeratedandfrozendoughsforwhichitisverysuitableasanacidcomponentoftheleaveningsystem.

3.2.3.2.9 CalciumacidPyrophosphate(CAPP)CAPPisutilizedinafewspecificapplicationssuchaswithryeflourdoughs,crack-ers,andfrozen(yeast)doughs,andfordoughstrengthening.

3.2.3.2.10 dimagnesiumPhosphate (DMP)Thisisaslow-actingacidsaltthatisheatactivated(40to44°C).Itmayneedtobeusedincombinationwithafasterleaveningagent.

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3.2.3.2.11 otheracidsVariousorganicacids,suchasadipic,fumaric,citric,andlacticacids,canbeusedasleaveningacids.Theymightalsobeconstituentsofformulaingredients(e.g.,souredmilkandcream,fruitjuices).Theyoftenactasnucleatingacidsforbakingpowders,andtheycanlowerthepHforspecialapplications.

... doughreactionrateandBatterreactionrate

Doughrateofreaction(DRR)isusedtomeasuretheCO2generatedduringmixingandholdingstagesinadoughsystem.Inordertobetterunderstandtheselectionofleavening acid for specificproduct applications, it is important tounderstand theDRR.ThetestquantifiesthepercentofCO2releasedfromdoughversustimefromthestartofmixing. Itmeasures the reactivityof leaveningacids (CO2generated)withsodiumbicarbonateduringmixingandthesubsequentbenchtimeofthedough(Conn,1981;Parksetal.,1960).LeaveningacidswiththesameneutralizingvaluesmighthavedifferentDRRvalues.Hence,theymayresultindifferentCO2releasingratesduringmixingandholdingstages.Thetestisusefulinthedevelopmentofleav-eningacidswithdifferentreactionratesintheactualdoughsystem.

DifferentformulaingredientsmayinfluencetheDRRvalueduetotheirdiffer-encesinacidity.Theflouristhemainconstituentprovidingtheacidity.Thelevelofgasproducedbytheflourdependsonfactorssuchasextractionrateandageoftheflour.Other formula ingredientsmayalsoaffect theDRRvalue.SugarmightdecreasetheCO2reactionratesupto10%dependingupontheamountofsugarintheformula.Becauseofitsacidity,milkhasasmalleffectonDRRvalue.However,calciumionscontributedbymilkslowthesolutionrateofmostleaveners,andthismightalsoaffecttheDRRvalue(Conn,1981;Parksetal.,1960).

Batterreactionrate(BRR)isdefinedasthetimerequiredforagivenpercentofreactiontotakeplaceatagiventemperaturebetweenaleaveningacidandsodiumbicarbonate.Usuallythetimeneededfor60%ofthereactiontotakeplaceismea-sured.BRRcanbeusedtoestimatewhenacertainpercentofreactionwilloccur.Thiscaneasilybedonebydeterminingtheproducttemperatureatdifferentstagesoftheprocess,especiallyduringbaking(Conn,1981;Parksetal.,1960).Thetestisusefultoinvestigatethebehaviorandsuitabilityofdifferentleaveningacidsinactualbattersystemswithvariousformulations.

... nutritionalvaluesofBakingPowders

Althoughmostbatteranddoughformulationsincludeonlyasmallquantityofbak-ingpowder(around1to2%),chemicalleaveningagentssupplyconsiderableamountsof calcium,phosphorus, sodium,andpotassium to softwheatproducts.Calcium,phosphorus,andsodiumcontentsofabakingpowdercontainingsodiumbicarbon-ate,SAS,MCP,andcalciumsulfatearearound60mg/g,15mg/g,and100mg/g,respectively (no potassium). On the other hand, calcium, phosphorus, and potas-siumcontentsofalow-sodiumbakingpowdercontainingpotassiumbicarbonateandacidicpotassiumsaltsarearound50mg/g,70mg/g,and110mg/g,respectively(nosodium).Hence,apieceofsoftwheatproductcontaining3gbakingpowdermaycontributearoundonequarterof theRecommendedDailyAllowances(RDAs)of

52748.indb 61 2/6/08 2:25:07 PM



calciumandphosphorus.(Foradults,theRDAforcalciumandphosphorusis800mg.) This contribution might be important, but consumers should read labels onproducts,becausethereisawidevariationintheircalciumcontents.Forexample,bakingpowderswithtartratecontainnocalcium.Somepeoplemayhavetousealow-sodiumbakingpowderinordertorestrictdietarysodiumintake.Fortunately,low-sodium baking powders are available in which the sodium salts have beenreplacedbypotassiumsalts.Theselow-sodiumbakingpowdershavesimilarleaven-ingproperties(Ensmingeretal.,1995).

... utilizationofBlendsofChemicalleaveningagentsandPremixes

Blendsofacidulantsarealsomarketedundervarioustrademarks.Thesecommercialblendsareusuallymixedwithadiluentsuchasstarch.Therefore,whenpurchasinganacidicsalt,theinformationshouldbeclearastowhetheritispurechemicalorindilutedform.Lackofknowledgemightcausecomplicationsduetotheincorrectproportionofsodiumbicarbonateacidmixturesindoughorbatter.

Somecookieformulationsincludealotofingredients,someofwhichareusedinverysmallquantities.Therefore,theweighingoperationsmightcauseproblems.Inmostindustrialprocessingunits,thesmallquantitiesofingredientsaremanuallyadded,andvarioussystemshavebeendevelopedtostreamlineoperations.Inevitableerrorsmightbeencounteredbecausethesesmallquantitiesofingredientsmustbeweighedrepeatedly,usuallyforeachbatcheveryday.Theerrorsmightoccurbothinaccuracyandinomission.Theoperationcanbesimplifiedbypreparingblendsofingredientssuitableforeachrecipe.However,thepreparationofahomogenousandstableblendisaprerequisite(Manley,1991).

Someoftheingredientsandleaveningagentsdonotdispersecompletelydur-ingdoughmixingduetovariousreasons.First,theirquantitiesareverysmallandthemixingactionof themixermightbeinsufficient todisperse themcompletely.Chemicalleaveningagentssuchassodiumbicarbonateandammoniumbicarbonatehaveatendencytolumpduringstorageorwhenwetted.Hence,itisoftennecessarytogrind,sieve,ordissolvetheminwaterbeforeaddingthemtothemixer.Therefore,therearesomeadvantagesofpreparingpremixes(Manley,1991):

ReducethenumberofseparateweighingoperationsforeachbatchofdoughReducetheincidenceofmeteringerrorsReducetheincidenceofingredientomissionsReducethemix-cycletimeforeachbatchofdoughbyallowingashortermixerloadingtimeImprovethemeansofmeteringleaveningagents(e.g.,pumpingratherthanmetering)andthepotentialforautomaticmetering

Because it is easier to meter liquids than solids, there is an interest in usingthedoughwaterasacarrier inpremixes.However, thesolubilityof thechemicalleaveningagentsmustbeconsideredbecausemostofthesesolublechemicalsformsaturatedsolutionsatquitelowconcentrations(e.g.,solubilityofsodiumbicarbon-ateisaround10gper100mlofwateratroomtemperature).Mixturesofchemical

••••

•

52748.indb 62 2/6/08 2:25:07 PM



leaveningagentsandotheringredientsmightbeincompatibleduetothepHofthepremixorchemicalreactionsresultinginlossofCO2orothergases.Furthermore,insomecases,theamountofwaterintherecipemightnotbesufficienttodissolvetheitemstobeincorporatedinthepremix(Manley,1991).

... effectofBatterviscosityandCoProduction rateontheQualityofsoftWheatProducts

Acakebatterisacomplexmixtureofingredients.Itisprincipallyanaqueoussys-tem,butithasanumberofdispersedphasessuchasstarchgranules,fat,andair.Iftheviscosityofthebatterisverylow,thephasesseparateeasily,evenbeforeenter-ingtheoven,resultingincakeswithinferiorquality.Suitablebatterviscosityslowstheseparationofphasessothattheseparationseemstobestoppedduringthetimerequiredtomakeacake.Duringmixing,airisincorporatedintothebatter.Afteritismixed,chemicalleaveningagentscannotgeneratenewgasbubblesinbatterordough.Duringmixing,airmustbeincludedinbatterordoughinordertosupplypreexistingbubbles.Airbubbleswithinthebatterordoughareessentialtoprovidenuclei.Othergases,producedbyyeastorchemicalleaveners,candiffuseintothesebubblesandexpandthem(Hoseney,1994).However,aircellscanbelostfromthebatterbyrisingtothesurfaceandalsobythecoalescingoftwocellsintoone.

As the batter is heated in the oven, at the beginning its viscosity decreases.Starchisdenseandmaysettle,formingatoughlayeratthebottomofthepanandalightfoam-likestructureatthetop.Abatterwithalowerviscositycannotkeepthegasbubblescollidingwith sufficient force to join together to form largerbubbles(coalesce).Althoughsmallgasbubblescanbetrappedinthebatter,largebubbleswillhavesufficientbuoyancytorisetothesurfaceofthebatterandtheyarelost.The heating of the batter is continued in the oven, and its viscosity increases inlaterstages.Thisiscausedmainlybystarchgelatinization.Asstarchgelatinizes,itswater-bindingcapacityincreasestoalargeextent.Hence,theviscosityofthebatterincreasestremendously,resultinginasolid-likeappearance.Thisiscalledsetting.Mostof theavailableCO2mustbereleasedduringexpansionandup toacertainstageofbakingbeforethedoughorbatterreachesitsset-pointtemperature.Thisismoreimportantforcakesthancookies.Ifthegas-releasingrateistoofast,acoarsestructure may result. The structure may collapse if the gas release is completedbeforethestructuresets.Ifthegas-releasingrateisextremelyslow,thevolumeofthefinalproductisusuallysmallerandstructuralrupturingorcrackingmayoccurduetotheeffectsofgasesreleasedaftersetting(Thacker,1997).Ofcourse,itshouldbekept inmindthatcarbondioxidegasexpandsmorequicklyathigheraltitudesandthereforehasgreaterleaveningaction.Therefore,thequantityofbakingpowdershouldbedecreasedwhenbakingathigheraltitudes.

Thebalanceof leaveningacidsandsodiumbicarbonateisalsoimportantandreachedbyusingtheneutralizingvalue tomatchtheamountof leaveningacid totheamountofsodiumbicarbonatesothatthehighestlevelofCO2isproduced.Ifaninsufficientamountofleaveningacidisadded,asmalleramountofCO2ispro-duced,andtheremainingsodiumbicarbonateincreasesthepHofthefinalproduct.Ifanexcessiveamountofleaveningacidisadded,gasproductionismaintainedat

52748.indb 63 2/6/08 2:25:08 PM



thesamelevel,butsomeoftheleaveningacidssuchasSAPPandGDLwillleaveabitteraftertasteinthefinalproduct.Forexample,theNVofpureSAPPis72,butitisalsoavailableinstandardizedformwithanNVof50.Foranapplicationthatutilizessodiumbicarbonateat2%offlourweight,standardizedSAPPwithanNVof50shouldbeaddedat4%offlourweighttoprovidetherightleaveningbalance:

250

100 43% %NaHCO SAPP× = (3.2)

ThetypeofleaveningacidusedintheformulationofbakingpowderalsoaffectstherateofCO2production,whichinturnaffectstheproduct.Forexample,dough-

Aldose Sugar N-substituted glycosylamine

Amadori rearrangement

Amadori rearrangement product (ARP)1-amino-1-deoxy-2-ketose

Reductones Fission products(acetol, diacetyl)

Schiff’s base ofhydroxymethylfurfural

(HMF) or furfural

Aldehydes HMF or Furfural

Aldols andN-free polymers

Aldimines and Ketimes

Melanoidins (brown nitrogenous polymers)

+ amino compound+ H2O

+ H2O

–2H2O > pH 7 –3H2O ≤ pH 7> pH 7

–2H +2H

– aminocompound+ amino

compound

+ aminocompound

+ aminocompound

–CO2 Strecker degradation

Dehydroreductones

+α amino acid

Figure 3.1 The major steps in the Maillard reaction.

52748.indb 64 2/6/08 2:25:10 PM



nutsrequirelittleleaveningduringmixing,andthenafastrateofCO2productionisrequiredsothatthebatterisleavenedquicklyandwillhavebuoyancytofloatonthehotoilduringfrying,ensuringacrispproduct.SAPPisgenerallyusedastheleaveningacid,sometimestogetherwithadditionalMCPforearlyactivityorGDLfordelayedactivity.

. MaIllardreaCtIon

AMaillardreactionisanonenzymaticchemicalreactioninvolvingcondensationofanaminogroupandareducinggroup,resultingintheformationofintermediatesthatultimatelypolymerizetoformbrownpigments.ThereactionwasfirstdescribedbyMaillard(1912).Hodge(1953)presentedaquitecompleteschemeoftheseveralstagesofthereaction,whichwasfullyapplied,anditisstillvalidtointerpretmanycharacteristicsoftheproductsandoftheMaillardreactionkinetics(Figure3.1).

ThechemistryoftheMaillardreactionincludesacomplexseriesofreactionsleading to the formationofavarietyofcompounds, includingflavorsandcolors,whichareoffundamentalimportancetodefinethequalityoffoodproducts.Therearethreemajorstagesofthereaction.Thefirststageconsistsofglycosylamineforma-tionandrearrangementofN-substituted-1-amino-l-deoxy-2-ketose(Amadoricom-pound).Thesecondstageinvolveslossoftheaminetoformcarbonylintermediates,whichupondehydrationorfissionformhighlyreactivecarbonylcompoundsthroughseveralpathways.Thethirdstageoccurringuponsubsequentheatinginvolvestheinteractionofthecarbonylflavorcompoundswithotherconstituentstoformbrownnitrogen-containingpigments,calledmelanoidins.

InadditiontothedesiredconsequencesoftheMaillardreaction,suchasthefor-mationsofcolorandflavor,thereareundesirableconsequencesinthermallyprocessedfoodsincludingbakeryfoods.Thechangescommonlyencounteredinthermallypro-cessedfoodsasaresultoftheMaillardreactionaresummarizedinFigure3.2.

MaillardReaction

Sensorial properties

Nutritional properties

• Formation of brown color• Formation of flavors

• Formation of antioxidants• Formation of antimicrobials• Loss of nutrients; i.e., lysine• Formation of toxic compounds,

such as acrylamide, HMF

Figure 3.2 Results of the Maillard reaction in bakery foods.

52748.indb 65 2/6/08 2:25:11 PM



3.3.1 FormaTionoFColor

Thecoloredproductsof theMaillardreactionareof twotypes: thehigh-molecu-lar-weightmacromoleculematerialscommonlyreferredtoasmelanoidinsandthelow-molecular-weightcoloredcompoundscontainingtwoorthreeheterocyclicrings(Amesetal.,1998).Colordevelopmentincreaseswithincreasingtemperature,timeofheating,increasingpH,andintermediatemoisturecontent(aw0.3to0.7).Ingen-eral,browningoccursslowly indrysystemsat lowtemperaturesand is relativelyslowinhigh-moisturefoods.ColorgenerationisenhancedatpH7.Ofthetwostart-ingreactants,theconcentrationofreducingsugarshasthegreatestimpactoncolordevelopment.Ofalltheaminoacids,lysinemakesthelargestcontributiontocolorformation,andcysteinehastheleasteffectoncolorformation.

Changeofcolorinbakeryfoodsduringbakingisadynamicprocessinwhichcertaincolortransitionsoccurasthebakingproceeds.ColorisusuallymeasuredinLabunits,whichisaninternationalstandardforcolormeasurementsadoptedbytheCommissionInternationaled’Eclairage(CIE) in1976(Papadakisetal.,2000). Incookies,thelightnessparameter(L)tendstodecreasewhilethechromaticparam-eters(aandb)increaseasthebakingproceeds,asillustratedinFigure3.3.

10 min 15 min 20 min 25 min 30 min

CIE

Col

or V

alue

Baking time, min

L

a

b

80

70

60

50

40

30

20

10

0

–100 5 10 15 20 25 30

Figure 3.3 Change of color in cookies during baking at 160°C. (See color insert after p. 158.)

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3.3.2 FormaTionoFFlavorandaromaComPounds

FlavorcompoundformationintheMaillardreaction(MR)dependsonthefollowing:

TypeofsugarsandaminoacidsinvolvedReactiontemperature,time,pH,andwatercontent(Jousseetal.,2002)

In general, the first factor mentioned determines the type of flavor compoundsformed,andthesecondfactorinfluencesthekinetics.

The most common route for formation of flavors via the Maillard reactionincludes the interactionofα-dicarbonylcompounds(intermediateproducts in theMR,stage2)withaminoacids through theStreckerdegradationreactions.AlkylpyrazinesandStreckeraldehydesbelongtocommonlyfoundflavorcompoundsfromtheMR.Forexample,lowlevelsofpyrazinesareformedduringtheprocessingofpotatoflakeswhen the temperature is less than130°C,but increase tenfoldwhenthe temperature is increased to160°C,anddecreaseat190°C,probablyowing toevaporationorbindingtomacromolecules.Thearomaprofilevarieswiththetem-perature and the time of heating. At any given temperature–time combination, auniquearoma,whichisnotlikelytobeproducedatanyothercombinationofheatingconditions,isproduced(vanBoekel,2006).

Thetotalamountofaminoacidsandreducingsugarsandtheirrelativepropor-tionsonthesurfaceofdoughduringbakingarethelimitingfactorsincrustaromaquality.Bothdependontheirformationfromenzymaticactivitiesandtheirinvolve-mentinmetabolicprocesses.Intensityofreactiondependsontemperatureandmois-ture in the oven (Kaminski et al., 1981). The type of aroma is influenced by theaminoacidstructure(El-Dash,1971),soglucoseplusleucine,arginine,orhistidinegivesafreshbreadaroma,whiledihydroxyacetoneplusprolinegivesacracker-typearoma(Coffman,1965).Sugartypeaffectsreactionratemorethanaromatype(El-Dash,1971).

Manycompoundshavebeendetectedindoughsandbreads(crustandcrumb),andtheyweresummarized(Coffman,1965;HansenandHansen,1994;Lundetal.,1989;Maga,1974;SchieberleandGrosch,1985,1987).Wheatandryeflourdoughsandbreadscontainmanycommoncomponents,butryeflourleadstoadditionalcom-ponentsnotidentifiedinwheatproducts(Maga,1974;SchieberleandGrosch,1985,1987).Thecompoundsidentifiedinpreferments,doughs,andbreadsarebasedonacids,alcohols,aldehydes,esters,ethers,furanderivatives,ketones,pyrrolederiva-tives,pyrazines,andsulfurcompounds(Maga,1974;SchieberleandGrosch,1985,1987).

Carbonyls(aldehydesandketones)canresultfrommanydifferentreactionsinbreadmaking (Maga, 1974).Someproceed from fermentation, such as acetoinordiacetyl (Lawrence et al., 1976), but the majority are produced during nonenzy-maticbrowningreactions(Johnsonetal.,1966).Also,somecarbonylcompoundsgeneratedduringfermentationcanvolatilizeduringbakingandappearagaindur-ingbrowningreactions(Johnsonetal.,1966).Breadcrustusuallycontainsalargernumberofcarbonylcompoundsthanbreadcrumb(El-Dash,1971).Lipoxygenaseisasourceofcarbonylsbydecompositionofhydroperoxides.Thus,linoleicacidpro-

••

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duceshexanal,inadditiontopentanolandotherproductsfromthepartialoxidationofhexanal.Likealdehydes,ketonesaremainlyformedduringMaillardreactions.Allaminoacidspromoteacetoneformationinthecrust,whichisalsoformedduringfermentation,aswellas2-butanone(Maga,1974).

Furanderivativesresultfromthermaldegradationofsugarsinbreadcrust.Someare intermediate compounds in Maillard reactions undergoing condensation withaminoacids.Theircharacteristicsaremoreinfluencedbyaminoacidthanbysugartype(Maga,1974).

Pyrrolederivatives,pyrazines,andsulfurcompoundsalsoproceedfromMail-lardreactions;somepyrazinescanbeprovidedbyflourormilksolidsincludedinformulation(Maga,1974).

Pyrazinesresultingfromthermalreactionsalsohavetypicalaromafeaturesabletobeimpartedtobread(Maga,1974).Finally,theleastvolatilefractions,suchasmelanoidins,dihydroxyacetone,ethylsuccinate,andsuccinicandlacticacids,con-tributemoretothetastethantothearomaofbread(Bakeretal.,1953).

3.3.3 FormaTionoFanTioxidanTs

ThereareseveralreportsontheformationofantioxidativeMaillardreactionprod-uctsinfoodprocessing.Pronyl-lysine,aMaillardreactionproduct,presentinbreadcrusthasbeendemonstrated tohavebeneficial effectsonhumanhealth (Linden-meieretal.,2002).Theadditionofaminoacidsorglucosetocookiedoughhasbeenshowntoimproveoxidativestabilityduringthestorageofthecookies(Summaetal.,2006).

Although the antioxidant effect of the Maillard reaction products has beenextensivelyinvestigated,theexactnatureoftheantioxidantsformedisnotyetwellknown.ItwasreportedthattheintermediatereductonecompoundsofMaillardreac-tionproductscouldbreaktheradicalchainbydonationofahydrogenatom.Maillardreactionproductswerealsoobservedtohavemetal-chelatingpropertiesandretardlipidperoxidation.Melanoidineswerereportedtobepowerfulscavengersofreactiveoxygenspecies(Hayaseetal.,1989).Recently,itwassuggestedthattheantioxidantactivityofxylose–lysineMRPsmaybeattributedtothecombinedeffectofreduc-ingpower,hydrogenatomdonation,andscavengingofreactiveoxygenspecies(YenandHsieh,1995).IntheMaillardreaction,highantioxidantcapacitywasgenerallyassociatedtotheformationofbrownmelanoidins(Aeschbacher,1990;Aneseetal.,1993,1994;Eichner,1981;GomyoandHorikoshi,1976;Hayaseetal.,1989;Kiri-gayaetal.,1968;Yamaguchietal.,1981;YenandHsieh,1995;YenandTsai,1993).Although in its early stages theMaillard reaction leads to the formationofwell-knownAmadoriandHeyn’sproducts(Ames,1988;Rizzi,1994),littleinformationisavailableonthechemicalstructureofthehundredsofbrownproductsformedbyaseriesofconsecutiveandparallelreactionsincludingoxidations,reductions,andaldolcondensationsamongothers(Eriksson,1981;Yaylayan,1997).

Anumberofparameterscanhelpinselectingtheprevalentmechanismoftheoverallreactionanditsrate,leadingtotheformationofdifferentchemicalspeciesthat are expected to exert different antioxidant properties. Inparticular, the anti-oxidantpropertiesofMaillardreactionproductshavebeenreportedtobestrongly

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affectedbythephysicochemicalpropertiesofthesystemandbytheprocessingcon-ditions (EichnerandCiner-Doruk,1981;Hommaet al.,1997;Huyghebaert et al.,1982;KimandHarris,1989;LingnertandEriksson,1981;Manzoccoetal.,1999;Obretenov et al., 1986; Stamp and Labuza, 1983; Waller et al., 1983). Moreover,itmustbekept inmind thatpolyphenols,ascorbicacid,andothercarbonylcom-pounds—evenifformedduringoxidativereactions—cantakepartintheMaillardreaction (Eriksson,1981;Rizzi,1994;Yaylayan,1997).Thecontributionof thesecompoundstotheformationofheat-inducedantioxidantsisstillunknown.

3.3.4 lossoFnuTriTionalqualiTy

The loss of available lysine is the most significant consequence of the Maillardreaction,anditisofthegreatestimportanceinthosefoodswherethisaminoacidis limiting, such as in cereals (Henle et al., 1991). Evaluation of the early stagesof the Maillard reaction can be achieved by determination of the furosine (ε-N-(furoylmethyl)-L-lysine)aminoacidformedduringacidhydrolysisoftheAmadoricompound,fructosyl-lysine,lactulosyl-lysine,andmaltulosyl-lysineproducedbythereactionofe-aminogroupsoflysinewithglucose,lactose,andmaltose(Erbersdo-blerandHupe,1991).Forthisreason,theestimationoftheextentofproteindamagecausedbyheatinginthefirststagesofthatreactionareoftenbasedondetermina-tionsoftheamountoffurosinethatisformedduringtheacidhydrolysisoffoods.Furosinedeterminationhasbeenusedincerealstocontroltheprocessingofpasta(Resmini and Pellegrino, 1994), bakery products (Henle et al., 1995), baby cere-als(Guerra-HernándezandCorzo,1996;Guerra-Hernándezetal.,1999),andbread(Ramirez-Jimenezetal.,2000;Ruizetal.,2004).

3.3.5 FormaTionoFToxiCComPounds

... acrylamide

OneofthemostsignificantconsequencesoftheMaillardreactionistheformationofacrylamide(Mottrametal.,2002;Stadleretal.,2002),whichwasfirstdiscoveredinthermallyprocessedfoodsinApril2002bySwedishresearchers(Tarekeetal.,2002).AcrylamideisclassifiedasaprobablehumancarcinogenbytheInternationalAgencyforResearchonCancer(IARC,1994).

Studiestodateclearlyshowthattheaminoacidasparagineismainlyrespon-sible for acrylamide formation in cooked foods after condensation with reducingsugars or a carbonyl source (Figure3.4). Moreover, the sugar–asparagine adduct,N-glycosylasparagine,generateshighamountsofacrylamide,suggestingtheearlyMaillardreactionasamajorsourceofacrylamide(Stadleretal.,2002).Inaddition,decarboxylated asparagine,whenheated, cangenerate acrylamide in the absenceofreducingsugars(Zyzaketal.,2003).Arecentstudyrevealedthat,besidesacryl-amide,3-aminopropionamide,whichmaybeatransientintermediateinacrylamideformation,wasalsoformedduringheatingwhenasparaginewasreactedinthepres-enceofglucose(GranvoglandScieberle,2006).

Incertainbakeryproducts,acrylamidecontentsup to1000mg/kghavebeenobserved(Croftetal.,2004).Thehighestcontentshavebeenfoundinproductspre-

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NH2 COOH

COOH

O NH2

Asparagine

Carbonyl compound

O

O

O

R

NH2 OH

N

H OH

R

N-Glycosyl conjugate

H2O

NH2 COOH

O

O

N

H

R

CO2

Schiff base

NH2

O

H

N

O

RR

O

O

H

NO

NH2

NH2

Decarboxylated Schiff base

Acrylamide

Figure 3.4 Formation of acrylamide during the pyrolysis of asparagine with glucose. (Adapted from Gökmen, V., and Senyuva, H.Z., European Food Research and Technology (DOI 10.1007/s00217-006-0486-7), 2007. With permission.)

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paredwiththebakingagentammoniumhydrogencarbonate,suchasgingerbreadproducts(Amreinetal.,2004;Koningsetal.,2003).Modelexperimentsshowedthatammonium bicarbonate strongly promotes acrylamide formation in sweet bakery(Biedermann and Grob, 2003; Weisshaar, 2004). Replacing this baking agent bysodiumhydrogencarbonatepresentsaveryeffectiveway to limit theacrylamidecontentofbakerygoods(Amreinetal.,2004;Vassetal.,2004).Inadditiontothebakingagent,thecontentofreducingsugarsandfreeasparagineaswellasthepro-cessconditionsinfluencetheacrylamideformationinbakerygoods(Amreinetal.,2004;Gökmenetal.,2007;Surdyketal.,2004;Vassetal.,2004).

Eventhoughthebakingtemperatureishighenoughtoproduceacrylamideinthecrust,thetotalbakingtimeisnotlongenoughtoincreasethecentertemperatureabove120°C,atwhichpointacrylamidebeginstoform.However,itwasshownthatacrylamide is present in both zones of the biscuit, but apparently lower amountsarefoundin thecenterof thebiscuit (Taeymansetal.,2004).Similar tobiscuits,thecrustandcrumbofbreadcontainsignificantlydifferentamountsofacrylamide(Surdyketal.2004).Thecrustlayershavebeenshowntocontainupto718μg/kgofacrylamidewhilethecrumbwasfreeofacrylamide(ŞenyuvaandGökmen,2005).Theseresultssuggestthatacrylamideformationinbakedcerealsmostlyoccursbyasurfacephenomenon.

Whenbiscuitsaretoastedtoanearburntstate,theacrylamideconcentrationisdecreasedbyupto50%(Taeymansetal.,2004).Similarresultshavebeenshownforseveralotherformsofcereals.Acrylamidelevelsinbiscuitsareincontrastwiththoseforthepotatobutareconsistentwiththesuggestionmadeelsewherethattheacrylamidecontentresultsfromabalancebetweenformationandelimination,withthelatterbeingmorerapidathighertemperature(Taeymansetal.,2004).

Ingredientsplayanimportantroleinacrylamideformationinbakeryfoods,asdifferentingredientshavevariousamountsoffreeasparagineandreducingsugars

SucroseGlucose

0 10 20 30 40

300

250

200

150

100

50

0

Amount of sugar in the recipe, g

Acry

lam

ide f

orm

ed, n

g/g

Figure 3.5 Effect of sugar type and amount on acrylamide formation in cookies dur-ing baking. (From Gökmen, V., Açar, Ö.Ç., Köksel, H., and Acar, J., Food Chemistry, 104, 1136–1142, 2007. Reprinted with permission from Elsevier.)

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precursors.Sugarsseemtobethemostimportantingredientinthedoughformulafromtheviewpointofacrylamideformation,because thefreeasparagine levelofwheatflourisrelativelylow.Notietal.(2003)reportedlevelsof150to400mg/kgofasparagineintensamplesofwheatflour.Surdyketal.(2004)measuredasparaginelevelsof170mg/kginwhitewheatflour.Figure3.5showstheformationofacryl-amideincookiesduringbakingasinfluencedbythetypeandamountofsugarsintherecipe.

Bakingtemperatureandtimearealsocloselyrelatedwithacrylamideformationinthebakingprocess.Thereisnoacrylamidepresentinuncookeddough,buttheacrylamidelevelriseswithtime.Incookiescontainingsucrose,acrylamideconcen-trationsshowedarapidincreaseafteraninitiallowerrateperiod,reachingaplateauwithin a baking time of 15 to 20 min at 200°C (Figure3.6). When sucrose wasreplacedwithglucose,theinitial lowerrateperioddisappearsandtheacrylamideconcentration of cookies increases rapidly, attaining the plateau values earlier asshowninFigure3.6(Gökmenetal.,2007).

Thetwomajorapproachestoreducingacrylamidelevelsincookiesarereplac-ingNH4HCO3byNaHCO3,andusingsucroseinsteadofreducingsugars(Grafetal.,2006).Incrackers,acombinationofthefirsttwoapproacheshasbeenevenmoreeffective(Vassetal.,2004),whichcouldalsoapplytootherproducts.Themeasurefocusingon the replacementof reducing sugarsby sucrose is limited toproductswherebrowningisnotofprimaryimportance.Theadditionofglycineduringdoughmakinghasbeenshowntoreduceacrylamideinflatbreadsandbreadcrustsupto90%(Bråthenetal.,2005).Amoderateadditionoforganicacidsmayalsobecon-sideredformitigationofacrylamideincookiesiftherecipeisformulatedwiththeinvertsyrupinsteadofsucrose.LoweringpHmayresultinexcessivehydrolysisof

420

360

300

240

180

120

60

0

0 5 10 15 20 25

Sucrose

Glucose

Baking time, min

Acry

lam

ide f

orm

ed, n

g/g

Figure 3.6 Changes in acrylamide concentration in cookies during baking at 200°C with time. (Adapted from Gökmen, V., Açar, Ö.Ç., Köksel, H., and Acar, J., Food Chemistry, 104, 1136–1142, 2007. Reprinted with permission from Elsevier.)

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sucrose,whichwillmakethecompositionmorefavorabletoformacrylamideduringbaking(Gökmenetal.,2007).Forcookiedoughthatincorporatessucrose, lower-ingthepHvaluefrom7.40to3.28bytheadditionofcitricacidhasbeenshowntoalmostdoubletheamountofacrylamideformedincookiesduringbaking.However,theadditionofcitricacidhaslimitedtheformationofacrylamideforcookiesincor-poratingglucose(Figure3.7).

... hydroxymethylfurfural(hMf)

Among themanyproducts formed,HMF,apossiblemutagen (Surhet al., 1994),seemsparticularly interestingbecauseof itsaccumulationduring thebakingpro-cess.AlthoughthetoxicologicalrelevanceofHMFisnotclear,asin vitrostudiesongenotoxicityandmutagenicityhavegivencontroversial results (Cuzzonietal.,1988;Janzowskietal.,2000;Leeetal.,1995),itspresenceisundesiredinthermallyprocessedfoods.

HMF is naturally formed as an intermediate in the Maillard reaction (Amesetal.,1998),andfromdehydrationofhexosesundermildacidicconditions(Kroh,1994)duringthermaltreatmentappliedtofoods(Figure3.8).HMFlevelsfoundincerealproductsarehighlyvariable.

Duringthebakingofbread,thewatercontentonthesurfacebecomeslowerthanthatinthecenter;thiscombinedwiththehightemperatureisoneofthefactorsthatmakesthecrustdifferentfromthecrumb(ThorvaldssonandSkjoldebrand,1998).HMFlevelsincrumbhavebeenfoundbetween0.6and2.2mg/kgandthoseincrustwerenotablygreater,from18.3tothe176.1mg/kginwhitebread(Ramírez-Jiménezetal.,2000).

300

240

180

120

60

0

3.28 4.37 7.40

pH

Sucrose

Glucose

Figure 3.7 The effect of dough pH on the amount of acrylamide formed in cookies hav-ing different sugars during baking at 205°C for 11 min. (From Gökmen, V., Açar, Ö.Ç., Kök-sel, H., and Acar, J., Food Chemistry, 104, 1136–1142, 2007. Reprinted with permission from Elsevier.)

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Carbonyl compound

R2

R2

R2

R2

R1R1

R1

R1

O

O

O

O

O O OH

COOHCOOH

COOH

OH

N

N

H

H

N

H

R2R1

O

N

H

OHN-Glycosylated

H2O

CO2

Schiff base

NH2

Amino compound

Hydroxymethylfurfural

Decarboxylated Schiff Base

Figure 3.8 Formation of hydroxymethylfurfural (HMF) as a consequence of (a) the Maillard reaction and (b) the pyrolysis of sugar.

α-D-Glucofuranose Hydroxymethylfurfural

OHOOO

OH

OH

OH

HO

HO–3H2O

∆

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Sugar amount in the recipe, g

Sucrose

Glucose

3.0

2.5

2.0

1.5

1.0

0.5

0.00 4010 20 30

HM

F, m

g/g

Figure 3.9 Effect of sugar type and amount on hydroxymethylfurfural (HMF) forma-tion in cookies during baking. (From Gökmen, V., Açar, Ö.Ç., Köksel, H., and Acar, J., Food Chemistry, 104, 1136–1142, 2007. Reprinted with permission from Elsevier.)

Baking time, min

HM

F, µg

/g

24

20

16

12

8

4

0

Sucrose

Glucose

0 5 10 15 20 25

Figure 3.10 Changes in hydroxymethylfurfural (HMF) concentration in cookies during baking at 210°C with time. (Adapted from Gökmen, V., Açar, Ö.Ç., Köksel, H., and Acar, J., Food Chemistry, 104, 1136–1142, 2007. With permission.)

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Thepresenceofahighamountofreducingsugarsintherecipemakesthedoughmoresusceptible to formHMFduringbaking (Figure3.9). Increasing thebakingtemperaturesalsoincreasestherateofHMFformationduringbaking(Figure3.10).

Thedoughcompositionanditschangesduringbakingarethemostcriticalfac-torsaffectingtheformationofHMFinbakeryfoods.Asthewateractivityofcook-iesdecreasesduringbaking, theconditionsbecomemorefavorabletoformHMF(Ameuretal.,2006).Theremovalofwatertoalevelcorrespondingtowateractivityof0.4ismostprobablyreflectingastageinbakingwherethetemperatureofcookiesbeginstoriseabove100°C,whichacceleratesHMFformationthermodynamically.Keepingthetemperaturebelow200°Cmaypreventanexcessivedecompositionofsucrose,andthusanexcessiveformationofHMFduringbaking.

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4 Cake Emulsions

Sarabjit S. Sahi

Contents

4.1 Introduction................................................................................................... 814.2 WhatAreEmulsions?................................................................................... 824.3 EmulsifierTypesandForms......................................................................... 834.4 ConceptofHydrophilic–LipophilicBalance(HLB)....................................854.5 FactorsAffectingtheStabilityofFoamsandEmulsions

inCakeBatters..............................................................................................874.5.1 InterfacialTension.............................................................................874.5.2 InterfacialRheology..........................................................................884.5.3 StabilizationbySolidParticles..........................................................884.5.4 SurfaceCharges.................................................................................884.5.5 DisproportionationandOstwaldRipening........................................ 894.5.6 FilmThinning.................................................................................... 894.5.7 FilmRupture...................................................................................... 89

4.6 ApplicationofEmulsifiersinCakeProduction............................................904.6.1 DispersionofShortening...................................................................904.6.2 ReductioninMixingTime................................................................904.6.3 ToReduceFatandEggContent.........................................................904.6.4 ToPrepareCakeMixes...................................................................... 91

4.7 MethodstoCreateCakeBattersandtheRolesPlayedbySpecificIngredients..................................................................................................... 914.7.1 FatsandShortening...........................................................................924.7.2 Water-SolubleProteins.......................................................................934.7.3 WheatFlour.......................................................................................93

4.8 ApplicationofEnzymestoGenerateSurface-ActiveMaterials...................944.9 Conclusion.....................................................................................................97SuggestedFurtherReading......................................................................................98References................................................................................................................98

. IntroduCtIon

Cakebattersareacomplexmixtureofnumerousairbubblesanddispersedfatpar-ticlesinacontinuousaqueousphase.Thebatterscanbedividedintotwocategories,those with high and low fat content. In batters with high levels of fat, the air ispredominantlybeatenintothefatphase,thuscreatinganunusualsystemwherethefoamistrappedinsidetheemulsifiedfatphasewhichisthenmixedintoanaque-ousphase.Inlow-fatorfatlessbatters,theairisoccludeddirectlyintotheaqueous

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phaseandthusformsaconventionalliquidfoam.Thedispersionofairandfatgener-atesconsiderableareaintermsofgas–liquidandliquid–liquidinterfaces,andthesenewlycreatedsurfaceshavetobestabilizedtopreventthedispersedphasesfromre-unitingandseparatingoutoftheaqueousphase.Duringbaking,afurtherincreaseininterfacialareaoccursasaresultofbubbleexpansion,andthisareaalsohastobestabilizedtopreventbubblesfromcoalescingandimpactingoncakequality.Interfa-cialpropertiesthereforeplayacrucialroleinboththebatterandthebakingstagesofcakeproduction.Thischapterreviewsinbriefanumberofthechemicalandphysi-calpropertiesofsurface-activematerialsandexplainssomeofthefunctionalrolesthatarerelevanttocakeemulsionsystems.Thetypeofimprovementsrequiredfromsurface-activematerialsarediscussed,andthewaystheseimprovementsarebroughtaboutareexplained.Theproductionofsurface-activematerialsin situbytheuseofenzymesisspecificallycovered.

. WhatareeMulsIons?

Bydefinitionanemulsionisadispersionofdropletsofoneimmiscibleliquidwithinanother.Theemulsionmaybeoil-in-watersuchasmilk inwhich theoildropletsaredispersedinacontinuousaqueousphase.Itmayalsobeawater-in-oilemulsioninwhich theaqueousphase isdispersed inacontinuousoilphase(e.g.,amarga-rine).Evenasimplefoamwhereairisdispersedinacontinuousliquidphasecanbeclassedasanemulsion.Withthesedefinitionsinmind,acakebattercanbeconsid-eredasacomplexemulsionsysteminwhichfatandairaremechanicallydispersedinacontinuousaqueoussugarphase.

Formationofanemulsionrequirestwoprocesses:First, theimmisciblephaseneeds to be dispersed into small uniform droplets. This is normally achieved byexpenditureofmechanicalenergy.Suchbreakdownoftheimmisciblephaseresultsinconsiderableincreaseintheinterfacialarea.Thisisathermodynamicallyunsta-blesituation,andthereisastrongtendencyforthedropletstocoalesce,eventuallyleadingtocompletephaseseparation.Thenewlycreatedinterfacialareaisstabilizedbysurface-activematerials,commonlyreferredtoasemulsifiersinthefoodindus-try.Surfactantsoremulsifiersarematerials thatconsistofmolecules thatpossessdualsolubilitywithinthesamemolecule.Thisispossibleasthemoleculesconsistofbothhydrophilicandhydrophobicparts.Thehydrophobicpartofthemoleculemayconsistofafattyacid,thelengthofwhichcanrangefrom12to18carbonatoms.Thehydrophilicpartofthemoleculemayconsistofglycerol,sucrose,orotherchemicalgroupings.Suchmaterialsaresurfaceactive—thatis,theyhaveastrongtendencytodiffusefromthebulkphase(usuallythecontinuousphase),inwhichtheyaredis-persed,toaccumulateatinterfacesbetweentheimmiscibleliquids.Theconcentra-tionoftheemulsifiermoleculesattheinterfaceresultsintheformationofinterfacialfilms.Itisthecompositionandthephysicalpropertiesofthesefilmsthatplayacru-cialroleinstabilizingdispersedphasesoncetheyareformedbymechanicalaction.

In thesamewayasanemulsioncannotbecreatedwithout theapplicationofmechanicalenergy,foamcreationrequirestheexpenditureofenergy,althoughfoamcanalsobecreatedby thevigorous introductionof air intoa liquidorwhengastrappedinaliquidissubjectedtoasuddendropinpressure.Emulsionsandfoams

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arethermodynamicallyunstable,andintheabsenceofadequatestabilization,itisonlyamatteroftimebeforethedispersedphaseisseparatedfromthecontinuousphase.Theonlyoptionafoodtechnologisthasistoslowtherateatwhichthevariousprocessesdestabilizefoamandemulsions.Thisisachieved,toadegree,bytheuseofsurfactantsoremulsifiers.

Thekeyphysicaleventsthatareimportantinrelationtoemulsionstabilityarecreaming(orsedimentation),coagulation,andcoalescenceof thedispersedphasedroplets.Creamingresultsfromdifferencesindensitybetweentheoilandtheaque-ousphases.Theinequalitybetweenthetwophasesshouldbekeptassmallaspos-sibletoassistinmaintainingtheuniformdispersionofthedispersedfraction.Theprocessofcoalescenceissomewhatmorecomplex.Coalescenceisinitiatedbydrop-letcoagulation,whichisfollowedbydisplacementofinterfacialmaterialfromtheregionofdropletcontact.Materialdisplacementwouldbeexpectedtobeeasierwithanexpandedfilmthanwithaclose-packedfilm.Thestabilityofanemulsioncantherefore be influenced by the correct selection of emulsifiers that form a close-packedor a condensedfilmat an interface.Optimumfilmproperties areusuallyachievedbyamixtureofsurfactants,typicallybycombiningoil-solubleandwater-solublesurfactantswhichgivestherequiredbalanceofhydrophilicandhydrophobicpropertiesintheemulsifiersystemforaspecificrecipeformulation.

Foamsconsistofliquidlamellaefilledwithgasandaredestabilizedandeven-tuallydestroyedbydrainageofliquidfromthelamellaeregionwhichleadstofilmrupture.Toslowtherateatwhichafoamcollapses,thedrainagehastobeopposed.Surfactantscandothisbycreatingsurfacetensiongradients.Theroleofsurfaceten-sionincreatingandstabilizingfoamsisunclear.Itiswidelyknownthatsurfactantsthatarehighlyeffectiveinreducinginterfacialtension,whichwouldbeexpectedtostabilize,actuallydonot,whereasothersthathavesimilarsurfaceactivityhavegoodfoamingpropertiesandstabilizefoamseffectively.Itwouldappearthatitistherateatwhichthesurfacetensionchangeswithsurfactantconcentration,ratherthanhowmuchitchanges,thatplaysakeyroleindistinguishingfoamingandemulsificationbehaviorofonetypeofsurfactantfromanother.

. eMulsIfIertyPesandforMs

Thereare twomain typesof surface-activematerials that areused in cakeman-ufacture: those derived from lipid-based materials and those based on proteins.Lipid-based emulsifiers have become increasingly important ingredients as cakemanufacturinghasbecomeamoreandmoremechanizedprocess.Intheearlydaysofcakeproduction,thekeyemulsifierswereeggsandlecithin.Thefunctionalityofthesematerialsisbasedonthepresenceofsurface-activelipoproteinsandphospho-lipids.However,thesenaturalemulsifierslackedtheeffectivenessandthedegreeoffunctionalityrequiredtowithstandtheseverityofcommercialmanufacturingopera-tionstoproduceproductswithsufficientlylongshelflife.

Thefirstwidelyusedchemicalemulsifiersweremono-anddiglycerides,formedbythereactionbetweenthefattyacidsoftriglyceridemoleculesandthealcoholglyc-erol.Theseearlyemulsifierscontainedapproximately40%oftheactiveingredient,themonoglyceride,therestbeingthenonsurface-activediglyceridewhichhaslittle

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ornoemulsifyingproperties.Forthisreason,theseearlyemulsifierswereusedatarelativelyhighlevelofabout3%.Thedevelopmentofthedistilledmonoglyceridesinwhichtheactivecomponentwasincreasedto90%ledtoconsiderablebenefitstothecakeindustry,allowingincreaseduseoffatandsugarintherecipeformulationresultingintheproductionofhigh-ratiocakes.High-ratiocakesarerichandmoisteatingandwithmuchimprovedkeepingqualities.Continuedimprovementsinemul-sifierproductshaveproducedfurtherbenefitstothemanufacturingprocessesaswellastothequalityofthecakes.Asignificantstepwastheemulsifierglycerolmonostea-rate(GMS),producedbyreactingstearicacid(C18)withglycerol.Itwasfoundthatestersformedwiththesaturatedfattyacidspossessedgoodcomplexingpropertieswiththeamylosefractionofstarch,resultinginimprovedantistalingproperties.

Otherderivativesofmonoglyceridesthathavebeenfoundtogiveusefuladvan-tagestocakequalityhavealsobeenproduced.Replacingglycerolwithpropyleneglycol and reacting it with stearic acid generates the emulsifier propylene glycolmonostearate(PGMS).Thisemulsifierhasfoundspecificusesintheproductionofenriched sponges—that is, spongesmadewithoil.ThePGMSwasdemonstratedtoformastrongfilmaroundthedispersedoildropletsand isolate themfromtheaqueousphase,hencepreventingtheoilfrominterferingwiththeprotein-stabilizedfoam.Anotherderivativeof themonoglycerides ismadeby reactingpolyglycerolwithselectedfattyacidtoproducepolyglycerolesters(PGE)offattyacids.

Thephysicalformofemulsifierssuchasthemonoglyceridesisimportantinordertoachievetheoptimumfunctionality.ItisgenerallyrecognizedthatemulsifierslikeGMSgivethebestperformancewhenhydratedtothemostactiveandwater-dispers-ibleα-crystallineform.ThisismostconvenientlyachievedbydispersingtheGMSpowderinaboutthreetimesitsweightofwaterheatedtoabout60to65°C,whenatransparenthomogenousliquidcrystallinelamellarphaseisformed(KrogandLars-son,1968).Inthisform,theemulsifierconsistsofbilayersofmonoglyceridemol-eculesseparatedbywaterlayersbetweenthepolargroups.Oncooling,thelamellarphasesetstoagelphase,theα-crystallinephasethathasthemostefficientwhippingandbatter-stabilizingproperties.Thisphaseisknowntobeunstableandonstoragebeginstoconverttotheβ-crystallineforminwhichthelipidbilayersarestackedontopofeachotherandthecrystalsarerelativelylarge,givingthiscrystallinephasepooraerationandcreamingproperties.Itisthereforenotusefulincakeproduction.TheactiveGMS isavailablecommercially inconvenient ready-to-usepaste forminwhichtheactiveformismaintainedbyincludingotheremulsifierssuchaspoly-glycerolestersorpolypropyleneglycolesters.Thepastecontainswater,andthishastobeaccountedforwhenadding thecorrectamountof theactive ingredient toaparticularrecipe.Inthisform,theytendtobemosteffectiveinfoamingpropertiesandemulsificationoftheoilintotheaqueousbatterphase.Emulsifiersthatformtheα-phasewhenhydratedarereferredtoasα-tending—examplesincludemonoglyc-erides,polyglycerolesters,andpolyglycolmonostearate.Ithasbeensuggestedthatthefilmsconsistingoftheseemulsifiers,afterexceedingthesolubilitylimit,solidifyasaresultofcrystallizationofthealignedmolecules.Whenthishappenstothefilmaroundoildroplets,thefilmessentiallyformsasolidphysicalbarrierbetweentheoilandwaterphase,preventingthetwofromcomingtogether.Thisprocesseffectively

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preventstheoilfrominterferingwiththestabilityoffoamstabilizedbyproteinsinthebatterstage.

Proteinmaterialwithemulsifyingpropertiescanbederivedfromegg,cereals,ordairysources,butthekeyrequisitepropertyissolubility.Proteinsmustbesolubleintheaqueousphaseinorderforthesurfacepropertiestobeexpressed.Theemul-sifyingpropertiesofeggyolkhavebeenattributedmainlytolipoproteinsbecauseoftheirabilitytointeractatthesurfacesofoildropletstoformproteinlayers,butotherproteinsarelikelytobeinvolved.Thepresenceoflipovitellin,lipovitellenin,andlivetincontributestoareductioninthedrainageoftheemulsifierfilminoil-in-wateremulsions.Lipovitelleninprovidesthebestoverallemulsionstability.Otherproteinsthathavebeenusedinoil-in-wateremulsionstabilityarecaseins,albumins,andglobulins.Moreinformationregardingtheroleofproteininfoamandemulsionswillbediscussedlaterinthechapter.

Itmustbepointedoutthatindividuallyboththelipid-basedemulsifiersandpro-teinsarecapableofformingfoamsandemulsions.However,foaminstabilityresultswhen the two types of surface-active materials are present together, particularlywhenthelipidemulsifiersarepresentatlowconcentration.ThisisdemonstratedinFigure4.1whereGMSwasaddedat0.25and0.75%tospongecakebattermixedtoadensityof0.65g/ml.Theeggisconsideredtobethefoamingagentinspongebatters(Figure4.1a),andthepresenceofsmallamountsofoilorfatreducesfoamstability.Figure4.1bshowssignsoffoaminstabilitywithbubblescoalescingtoformlargerbubbles.Cakesbakedwith0.25%GMSdisplayedseverecoresorcollapse,indicatingbreakingofthefoamcreatedduringmixing.CakesmadewithnoGMSwereofgoodvolumebutwithfairlyopencrumbstructure.ThiswouldsuggestthattheproteinandGMSdonotcombinetogethertostabilizeinterfacialfilmsaroundthegasbubbles.At0.75%additionofGMS,Figure4.1c,thereweregreaternumbersofgasbubbleswithuniformsizedistributioncomparedwith0.25%addition.Thespongecakespro-ducedgoodvolumeandcrumbstructurewithnocoringpresent.TheresultswouldindicatethattheGMSat0.25%isnotpresentinsufficientquantitytostabilizegasbubblesatthebatterorthebakingstagebutisabletointerferewiththeprotein–pro-teininteractionsstabilizingthegasfilms.Atthe0.75%level,theGMScompletelyreplacestheproteinfilmsandisabletosaturatetheair–liquidinterfacecreatedbythemixingprocessandmaintainstabilityduringthebakingstage.

. ConCePtofhydroPhIlIC–lIPoPhIlICBalanCe(hlB)

Inchemical terms,themolecularstructureofemulsifiersconsistsofpolar(water-loving) and nonpolar (oil-loving) groups. Emulsifiers can be classed by a systemcalledhydrophilic–lipophilicbalance (HLB). It is awayof indicating theoverallattractionofanemulsifiertoeitherwateroroil.TheHLBscalerangesfrom0to20,with1indicatingatotallyoil-solublematerialand20indicatingahighlywater-sol-ublematerial.GMS,forexample,hasaHLBvalueof3.8andisoilsoluble,whereashigh-monoester-contentsucroseesterpossessesaHLBof15andissolubleinwater.Incidentally,diglycerideestershaveaHLBvalueof0andthereforehavepooremul-sificationproperties.Infact,ifpresentinsufficientamountswithmonoglycerides,diglycerides can actually be detrimental to the functionality of monoglycerides,

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andhencethewidespreaduseofdistilledmonoglyceridesthatcontainlowlevelsofdiglycerides.HLBnumbersarealsoindicativeofwhichtypeofemulsionaparticularemulsifieroramixtureofemulsifierswouldbemostlikelytoform.Forexample,theoil-solubleGMSwouldstabilizeawater-in-oilemulsionsuchasmargarine.Ontheotherhand,thewater-solublesucrosemonostearatewouldbesuitableasastabilizerofanoil-in-wateremulsionsuchasacakebatteroramayonnaise.EmulsifiertypesofintermediateHLBarenotgoodemulsifiersbuthavegoodwettingproperties.TheHLBsystemworkswellwithbasicemulsionsystemswherethereductionofinterfa-

200 µm

a

200 µm

b

200 µm

c

fIgure. Influence of glycerolmonostearate (GMS) concentrationongasbubblesinspongebatters:(a)control batter—protein-stabilizedaqueousfoam;(b)0.25%GMS—dis-ruption of protein-stabilized bubble;(c) 0.75% GMS—foam stabilizationby emulsifier alone. (Courtesy ofCampden&ChorleywoodFoodRA,ChippingCampden,UK.)

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cialtensionandthestabilizationofthedispersedphasearethekeyrolesrequiredoftheemulsifiersystem.However,cakesystemsaremorecomplex,andotherfactorsinadditiontotheinterfacialpropertiesareinvolved.Thisisdemonstratedbythefactthatthebestresultsareusuallyobtainedbytheuseofablendofemulsifierswithdifferenthydrophilicandlipophilicproperties.Also,theHLBsystemcannotpredictwhichHLBvaluewillproduceoptimumemulsifierstability.Thisandotherimpor-tantfactors,suchasconcentrationoftheemulsifierstobeused,therelativeratioofthetwoimmisciblephases,andthemeansbywhichtheemulsificationprocessistobeachieved,havetobedeterminedexperimentally.

. faCtorsaffeCtIngthestaBIlItyof foaMsandeMulsIonsInCaKeBatters

Cakebattersmadewithfatoroilrepresentaclassicalemulsionsystemoffatdis-persedinacontinuouswaterphase.Coupledwiththatisafoamsystem,initiallyinthefatphasebutbeingtransferredtotheaqueousphasewhenthefatmeltsduringbaking,resultinginacomplexemulsionandfoamsystem.Ithasbeendemonstratedthattheaircellsinafatparticlewillcoalescewithinthefatparticleratherthantrans-ferasdiscreteaircellstotheaqueousphase(ShepherdandYoell,1976).Inthesamepublication,itwasobservedthatairbubblesreleasedfromthefatphaseonmeltingremainedattachedtothefatsurface,suggestingthatthefatsurfacemaybecoatedwitheggproteinsoraddedemulsifiersduringmixingwhicharetransferredtothegasbubbleswhentheytransferfromthefattotheaqueousphase.Continuedheat-ingofthebatterduringbakingcausesrapidexpansionofthebubbles.Atthispoint,theviscoelasticpropertiesofthefilmssurroundingthegascellsbecomeimportantinthemaintenanceoftheintegrityofthebubbles.Expansionceaseswhenthecakestructureissetandthediscretefoamsystemsbreaktoformanopennetworksponge.Atpresent,thereisnoestablishedmechanismtoexplainhowcomplexsystemslikecakeemulsionsarestabilized,butsomeprogresshasbeenmadetohelpexplaintheessentialrolesplayedbykeyingredients.However,thereareanumberoffundamen-talfactorsthatgovernemulsionstability,andthesearealsolikelytoaidthestabilityofthedispersedfractionsinacakebattertosomedegree.

4.5.1 inTerFaCialTension

Itisacceptedthattheinterfacialtensionbetweenthedispersedphaseandthecontinu-ousphaseisanimportantfactorincontrollingstabilityinsuchsystems.Ahighten-sionbetweenthetwophasesislikelytobedetrimentaltoemulsionandfoamstability,whereasa low tension,asa resultofsurface-activemoleculesaccumulatingat theinterface,islikelytobebeneficialinstabilizingsuchsystems.Theinterfacialtensionbetweenoilandwaterinthepresenceofemulsifierscanrangefrom1to10mN/m.Surface-activematerialsnaturallypresent inkey ingredientsused incakesystemsandaddedemulsifierscanthereforestabilizeemulsions.Interfacialmeasurementsaresensitivetothecompositionoftheinterfaceandcanbeusedtoidentifythenatureofthepredominantmaterial,forexamplelipid-basedsurfactantorproteins.MethodstomeasuresurfaceorinterfacialtensionsincludetheRingmethod,theWilhelmyplate

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method(Shaw,1980),aswellasanumberofmethodsbasedonimagingapendantdrophangingfromthetipofacapillarytube(AmbwaniandFort,1979).

4.5.2 inTerFaCialrheoloGy

Therheologicalpropertiesoftheinterfacialfilmsplayakeyroleinstabilizingdis-persed phases.The rheology is chiefly governed by the composition of the inter-facialregion.Proteinadsorptionataninterfaceusuallyresultsintheformationofa two-dimensional viscoelastic film, whereas lipid-like materials form relativelythinmobilefilms.Filmrheologycanbemeasuredusingeithershearordilatationalmethods.Surfaceshearmeasurementsareusuallyperformedwitharingorabiconelocatedattheinterface,andthefilmisdeformedwithanoscillatorystressorstrain.Theanalysisoftheappliedstressorstrainandtheresultingresponsecharacterizestheviscoelasticpropertiesoftheinterface.Thistechniquewasusedtodemonstratethedisruptiveinfluenceofflourlipidsonprotein-stabilizedinterfacialfilms,givingan insight into the negative effect that such materials can haveon foam stability(Sahi,1994).Thedilatationalapproachagaininvolvesoscillatorymethods,butherethe surfaceareaof the interface ischangedand thechange in surfaceor interfa-cial tension ismonitored.Thismethod isuseful for studyingmixedfilmsystemssuchasprotein–lipidmixtures.Whereasdispersedphasesstabilizedbylipid-basedmaterials(emulsifiers)influenceemulsionandfoamstabilitythroughtheireffectsoninterfacialtension,protein-basedstabilizationarisesfromthephysicalpresenceoftheadsorbedfilmratherthanfromareductioninthetensionofthedispersedphaseinterfaces. Such films can be many layers thick and viscoelastic and are able todampenperturbationsexperiencedintheinterface.

4.5.3 sTaBilizaTionBysolidParTiCles

Emulsionscanalsobestabilizedbythepresenceofsolidparticlesattheinterface.Finelydispersedsolidsthathaveacontactanglebetween0and180°haveanaturaltendencytocollectatanoil–waterinterface.Whendispersedparticlescomeclosetooneanother,thephysicalpresenceofthesolidparticlespreventsonedropletfromtouchinganother.Suchamechanismmaybesignificantincakeemulsionswherethepresenceofeggandflourparticlescouldcontributetoemulsionstability.

4.5.4 surFaCeCharGes

Electrical double-layer repulsion is an important stabilizingmechanism inoil-in-wateremulsions.Thesurfacechargesonthedropletscanrepeldropletswhentheycomeclosetogetherbythemutualrepulsionoftheirelectricaldoublelayers(Ber-genstahlandClaesson,1990).Theemulsifiersinacakerecipeformulation,presentbothnaturallyandasadditives,onadsorptiontoanoil–waterinterfacewillhaveanoverallnegativeelectricalcharge.Inthisrespect,flourcancontributelipoproteinsaswellaspolarlipids;forexample,phospholipidsandsimilartypesofmaterialsarealsopresentinegg.Whensuchmaterialsareadsorbedontooilorfatdroplets,anoverallnegativechargeresults,whichwillpreventclosecontactofthedropletand

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Cake Emulsions

contributetowardemulsionstability.Chemicallysynthesizedemulsifiersareabletorepeloildropletsinasimilarfashion.

4.5.5 disProPorTionaTionandosTwaldriPeninG

Disproportionationistheprocessbywhichlargegasbubblesgrowattheexpenseofsmallbubbles.ThisispredictedbyLaplace’sequationthatstatesthatthepressureinabubble(Pbubble)willbe

P P 4

Rbubble a= +γ

(4.1)

wherePaistheatmosphericpressure,γisthesurfacetensionoftheliquid,andRistheradiusofthebubble.

Gaswilldiffusefromasmallerbubbletoalargebubbleincontactwitheachotherdrivenbythepressuredifferentialbetweenthebubbles.Thismechanismsug-geststhatinordertoobtainauniformdistributionofbubblesinacakebatter,theinterfacialtensionmustbeaslowaspossibleinordertodecreasethevalueoftheexcesspressurethatwouldincreaseasbubblesizebecomessmall.

Ostwaldripeningoccursinemulsionsandiscausedbythediffusionofliquidfromsmallerdroplets into largerones.Largerbubbles thusgrow larger and thenaremoresusceptibletocoalescence.AuniformdistributionofdropletsizehelpstostabilizeanemulsionwithrespecttoOstwaldripening.

4.5.6 FilmThinninG

Filmthinningbehaviorprovidesinsightintothefactorsthatpromotefoamandemul-sionstability.Thinningoccursasaresultofgravitationalforces,andtheviscosityoftheaqueousphaseplaysanimportantrole:thehighertheviscosityoftheaqueousphase,thesloweristherateoffilmthinning.Thecompositionofthefilmplaysanimportant role incontrollingandmaintaining thickness.Forexample, lipid-stabi-lized films exhibit rapid drainage (Clark et al., 1990), whereas protein-stabilizedfilmsdisplayslowdrainage(Clarketal.,1994).

4.5.7 FilmruPTure

Filmthinningeventuallyresultsinfilmrupture.Asmentionedpreviously,proteinsformstrongviscoelasticfilmsthatresistrupture.However,lipidfilmstendtopossesslowlateralcohesion,andlocalizedstressesofthefilmcauseittoexpand,resultinginadecreaseofsurfactantconcentrationintheregionofstressandanincreaseinsurface tension(theGibbseffect).Becauseafinite time is requiredforsurfactantmoleculestodiffusetothisregiontorestoretheoriginalsurfacetension(theMaran-gonieffect), the increasedsurface tensionmaypersist longenough torecover theoriginalthickness.TheabsenceoftheGibbs–Marangonieffectisthemainreasonwhypureliquidsdonotfoam.

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. aPPlICatIonofeMulsIfIersInCaKeProduCtIon

Therearenumerousreasonswhyemulsifiersareusedinthemanufactureofcakes.Primarily, theseincludefoaming,emulsification,andbatterstability.Furtherben-efits include thehomogeneousdispersionof fat in thebatter, greater tolerance torecipeformulationchanges,andthepossibilityofchangingfrommultistagemixingtoanall-inmixingmethod.Emulsifiersalsogivecakesatendereatingqualityaswellashelptoimproveshelflife.Thelatterisimportantforindustriallyproducedcakes,asthereisconsiderablelengthoftimebeforetheyreachtheconsumer.Theuseofemulsifiershasalsoledtokeychangesintherecipeformulationsfromtheearlierpoundcaketothehigh-ratiocakesmadetoday.Someofthekeyfunctionsofemulsifiersaredescribedinmoredetailbelow.

4.6.1 disPersionoFshorTeninG

Usingshorteningaloneinahigh-ratio-typerecipecanresultinthebattercurdlingduringmixing.Thiscanbeavoidedbyinclusionofanemulsifierduringproduc-tionoftheshortening,suchashorteningbeingreferredtoashigh-ratioshortening.EmulsifierssuchasGMSandmono-anddiglyceridesareusedinsoftfatsatlevelsupto10%tomanufacturehigh-ratioshortenings.Becauseofthefunctionalityoftheemulsifier,theseshorteningscanbeeasilydispersedinhigh-ratiobatterswith-outcurdling.Cakemargarinesalsocontainemulsifiersaddedbythemanufacturer,bothtomaintainasmoothproductandtofacilitateeasydispersioninthebatter.Inaddition,emulsifierinclusioncanimprovecreamingpropertiesinbothshorteningsandmargarines.

4.6.2 reduCTioninmixinGTime

Specific emulsifiers such as GMS, polyglycerol esters, and lactic acid esters ofmonoglyceridespossessmarkedfoam-promotingproperties.Whenaddedtospongebatters (0.5 to1.0%ofbatterweight),whisking timecanbegreatlyreduced.Theemulsifiersdo thisby reducing the interfacial tensionof the aqueousphase, thusallowingthemixingactiontobreaktheinterfacemoreeasilyandtoincorporateairintothebatter.Theloweringoftheinterfacialtensionalsoaidsthebreakupoftheairbubbles toproduceasmallerandmoreuniformcellularstructureof thecake.Anadditionaladvantageisamorestablebatter,resistanttomechanicaldepositingstressesandmoretoleranttovariationsinholdingtimeaftermixing.

4.6.3 ToreduCeFaTandeGGConTenT

Foam-promoting emulsifiers such as GMS, polyglycerol esters, propylene glycolesters,orblendsofthesecanhelptoreducethefatcontentofacakeorsubstitutionofthefatbyasmallerquantityofvegetableoil.Oiladditionwasoriginallyfoundtogivelowvolume,opengrain,andpoorstructureofthecake.However,theuseofthecorrectemulsifierorblendsofemulsifierscanproducecakesofgoodquality,usingoilinsteadofhardfat.Emulsifierscanalsobeusedtoreplacepartoftheegginspongecakes.Insuchacase,theaerationpropertiesoftheeggareperformedbythe

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Cake Emulsions

emulsifier,andeggcontentcanbereducedsufficientlytosupportthefoamstructureandcontributetotheeatingqualityofthecake.

4.6.4 ToPrePareCakemixes

Emulsifiersare includedindrycake-mixformulationsto improvebatteraeration.Specialcold-water-dispersibletypesareavailableconsistingofamixtureofemul-sifierssimilar to those found inpasteemulsifiersbutdriedontoacarrier suchasskimmedmilkpowder.Spray-driedemulsionsofcakeemulsifierssuchasdistilledmonoglycerides,propyleneglycolmonostearate,andlactylatedmonoglyceridescon-taininganonfatmilkpowderasacarrierareusedinspongecakeswiththesamebenefitasaqueousgels.

Practical experience shows that combinationsof emulsifiers areusuallymoreeffective than any single emulsifier used alone, suggesting synergistic effectsbetweenblendsofemulsifiers.Ablendoftwooreventhreeemulsifierscanbeused;anexampleofablendwidelyusedismono-diglycerideestersandpolyglycerolestersofmonoglycerides.

. MethodstoCreateCaKeBattersand therolesPlayedBysPeCIfICIngredIents

A cake batter is formed from a basic formula consisting of flour, fat, sugar, andegg.Theingredientscanbemixedinstagesusingthecreamingmethod(sugarandshortening),theflourbattermethod,ortheall-inmethodwherealltheingredientsareaddedsimultaneouslyintothemixingbowl.Inthecreamingmethod,thefatandsugararefirstmixedtogethertoaeratethemixture.Smallairbubblesareintroducedintothedispersedparticlesoffat.Optimumaerationof thebatterdependsonthesizeofthefatcrystals,andsmallcrystals(β′-form)givethebestaerationproperties(Hoerr,1960).Suchcrystalsareable toorientate themselvesaround thegascellsandprovideaprotectiveshell.Theamountofairtrappedinthecreamingprocessisimportanttothestructuredevelopmentofthecakeasnonewgascellsarecre-atedduringtheremainingstagesofthecake-makingprocess(Carlin,1944).Intheflourbattermethod,theshorteningandtheflouraremixedtoformanaeratedmass,andinaseparatecontainertheeggandsugararewhippedintoafoam.Thetwoarecombinedwiththeadditionoftheotheringredientsatthesametime.Intheall-inmethod, all thekey ingredients aremixed intoa smoothbatter.Themixingof afat-containingbatterresultsintheformationofafatemulsionwithairbubblesalsobeingtrappedintheemulsifiedfat.Aerationoffatlessrecipesoccursintheaqueousphase,with eggproteinsplaying an important role aswhipping agents and foamstabilizers.Theimportantprocessesarethehomogenousmixingoftheingredientstocreateasilkysmoothbattercontainingalargevolumeofairintheformofsmallcellsinthefatphaseortheaqueousphasedependingontherecipe.Intherespectivemixingmethods,themajoringredientsplayakeyroleateachstage.Thecontributionofeachingredientisexaminedwithrespecttofoamformationandemulsification.

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4.7.1 FaTsandshorTeninG

Thefunctionalpropertiesoffatsplayakeyroleinbakeryproductsingeneral,andthisisespeciallyimportantintheproductionofcakes.Thefunctionalityofplasticfatsisinfluencedbytheratioofliquidoiltocrystallinesolidsaswellasthecrystal-lineformachievedduringtheprocessing.Thetwofundamentalfunctionalproper-tiesoffatsarecreamingandemulsification.Theprocessofcreamingfatwithsugarresultsinthebreakupofthefataswellasthetrappingofairintothedispersedpar-ticlesoffat.Thisstageofthemixingthereforehasacrucialbearingonthevolumeofcakethatcanbeachievedattheendofbaking.Theplasticityofthefatandtheparticlesizeofthesugararebothimportantinachievingoptimumfatparticlesizeandairincorporation.Castersugarwithparticlesizespecificationof<10%above425μmand<22%below212μmistypicallyusedasitpossessestheoptimumsur-faceareatobreakdownthefat.

Inadditiontotheaerationcapacityofthecakeshortening,thecrystallinityofthefathasbeensuggestedtocontributetostabilizationofthefoaminthebatteranddur-ingbaking.Thefatcrystalswiththebestfunctionalityaresmallandneedleshapedandcanalignthemselvesattheinterfaceofairbubblestrappedintothefatdroplets(Brooker,1993),thusstabilizingtheairbubblestrappedduringthecreamingpro-cess.Thesameresearcheralsohypothesizedthatthefatcrystalscomeoutofthefatdroplets,andas theyemergeintotheaqueousphaseof thebatter,becomecoatedwithsurface-activewater-solubleproteins.This thenconferssurfaceproperties tothefatcrystals,whichthenalignattheair–waterinterfaceinthebatter.Duringthebakingprocess,theairbubblesexpand,generatingnewinterfacialareathatneedstobestabilizedtopreventruptureofthefoambeforesufficientexpansionhasbeenachieved.Thetimelymeltingofthefatcrystalsreleasesthesurface-activeproteinsadsorbed on the fat crystal. This protein then becomes available to stabilize theexpandingairbubbles.Thefatcrystalsthereforeactasareservoirofsurface-activematerialthatisincloseproximitytothegasbubblesastheyexpand.

Recentworkontheroleoffatinthestabilizationofairin“all-in-one”cakebat-tershasshownthatfatcrystalsareejectedfromtheemulsifiedshorteningduringmixing,becomeenvelopedbyafat(crystal)–waterinterface,andareabletostabilizelargenumbersofsmallairbubblesbyadsorbingtotheirsurface.Duringbaking,airbubblescanexpandwithoutrupturingbecauseofextrainterfacialmaterialprovidedbytheadsorbedfatcrystalswhentheymelt.Theoutcomeofthismechanismisthatabattercanexpandduringbakingwithoutcollapsetoproduceahigh-volumecakeoffinecrumbstructure.

Theuseoffluidshorteningsisontheincreaseincakemanufacturingandotherbakerysystems.Inthepast,theywerefoundtobedetrimentaltocakequality,result-inginpoorcrumbqualityandlowcakevolume(Knightly,1988).Thiswaslargelyovercomebytheuseofareducedamountoftotalfatintherecipeandacarefulcom-binationofhydrophilicandhydrophobicemulsifiersdispersedinfluidshortenings.Fluidshorteningsaremixturesofhardfatandsurfactantsinvegetableoil.Typicalsurfactantsusedareacombinationofmonoglycerides, lactylatedmonoglycerides,andpropyleneglycolesters.Thelevelofemulsifierusedcanbequitehighat10to15%oftheoilweight.Theadditionoftheemulsifierintheα-crystallineformispar-

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Cake Emulsions

ticularlyeffective.Inthisform,theemulsifiersystemisabletoemulsifytheoilintofineparticlesintheaqueousphaseand,asaresult,shieldtheprotein-stabilizedfoamfromthedestabilizingeffectoftheoil.Otherbenefitsoftheseshorteningshavealsobeenrealizedinrecenttimes.Healthconcernsregardingtheintakeofsaturatedfatsandtransfatshaveledtoreplacementoftheplasticshorteningsandthechallengetotheindustryhasbeentoachievethiswithoutlosingthebenefitsderivedfromthem.Fluidshorteningsthatproducefinishedproductsidenticaltothosemadewithplasticshorteningshavebeendevelopedbyusingα-stableemulsifiergels.

4.7.2 waTer-soluBleProTeins

Proteinnaturallypresentineggandflouraregoodfoamandemulsionpromotersandstabilizers.Inorderfortheproteintobesurfaceactive,itmustpossessgoodsolubil-ityinanaqueoussystem.Examplesofsuchproteinsincludealbuminsandglobulins.Themechanismbywhichproteinsfunctionatinterfacesisdifferentthanthatofthelipid-basedemulsifiers.Proteinmoleculesdiffusefromthebulkofthesolutiontotheair–wateroroil–water interface.Onreaching the interface,somesegmentsofthemoleculesattachthemselvesandsomeunfoldingoftheproteinchainmayalsooccur.Intermolecularinteractions,forexampleH-bondingbetweensectionsoftheprotein chains, link theneighboringpolypeptide chains together.Further adsorp-tionofproteinsunderneaththeprimaryinterfaciallayercanleadtotheformationofathick,viscoelasticinterfaciallayerthatisabletostretchwithoutbreakingandhenceabsorbfluctuationsintheinterfacialregion.Thephysicalpresenceofthethickproteinfilmalsopreventsbubblescoalescingoncontactwitheachother.Itmustbeemphasizedthatproteinsarenotaseffectiveaslipid-basedsurfactantsinreducinginterfacial tension. For example, commonly used emulsifiers can lower air–watertensionto30mN/morlower,whereasthelargeproteinmoleculeswithlimitednum-berofhydrophobicsitesintheirpolypeptidechainscanonlyattainvaluesofabout45mN/m.However,theloweringoftheinterfacialtensionisnottheonlyrequire-mentinfoamandemulsionsystems.

4.7.3 wheaTFlour

Wheatflourusedincakeproductioncontainsnumerouscomponentsthatcanplayvariousroles infoamandemulsionstability.Theproteinsand lipidsareasourceof surface-active materials that have the capacity to accumulate at the air–waterandoil–water interfaces.Wheatflouralsocontains threemajor typesofpolysac-charides—starches,hemicelluloses,andβ-glucans.Starchesfromheat-treatedandchlorinatedfloursallowbetterabsorptionofliquidinthebatter;hence,battersmadefromtreatedflourshaveahigherviscositycomparedwithbattersmadewithuntreatedflour.Thishasapositivebenefitonaerationofthebatter,asaircanbetrappedandsubdividedmoreeasilyand thebubbleshavea lesser tendency tofloatoutof thebattercomparedwitha less-viscoussystem.Batterviscosity isalso influencedbythehemicellulosematerialthatispresentat2to3%oftheflourmass(MontgomeryandSmith,1956).Thehemicelluloseshavetwoforms,denotedbytheirsolubilityinwater: insolublematerialsandsolublematerials.Botharecomposedofmainlyarabinoxylansandarecommonlyknownaspentosans.Inlinewithotherhydrocol-

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loids,theyhavetheabilitytobindeighttotentimestheirownweightinwater.Thisisbeneficialatthebatterstagewherewaterabsorptionbythesematerialsincreasesbatterviscosity.Theβ-glucansalsocontributetobatterviscosityinasimilarfash-ion.Thehemicelluloseshavealsobeenshowntopossesssurface-activeproperties.Izydorczyketal.(1991)reportedthatarabinoxylansandarabinogalactansreducedthesurfacetensionofwaterfrom72to52and50mN/m,respectively.Thesevaluesaresimilartothesurfacetensionvaluesreportedforsomeproteins,suggestingthatthesematerialsinwheatflourcouldpotentiallyactasfoamandemulsionstabilizingmaterials.Hemicellulosetypesofmaterialsarebelievedtostabilizefoamfilmsbyretardinggasdiffusion through thegas–film interfaceoractingasstericstabiliz-ersof thefilmssurrounding thegasbubbles(Prins,1988).Although thefoamingpropertiesofthearabinoxylansandarabinogalactanswereinferiorcomparedtotheproteinbovineserumalbumin,theviscosityandelasticityoftheinterfacialfilmsur-roundingthegasbubblesislikelytobeimportantforfoamstability.

Thestarchfractionin thewheatflourdoesnotappear toplayadirectrole inthe stabilization of foam or emulsion systems in cake batters. However, starchdoesabsorbwaterintherecipe,andtheamountofwaterabsorbedisincreasedbychlorinationorheattreatmentofthecakeflour.Thisgivesincreasedviscositythathelps to trapand subdivideair in thebatterduringmixing. Itmightbeexpectedthat,becausestarchgranuleshavealargesurface-area-to-volumeratio,interactionsbetweenstarchandemulsifiersmayinfluencegasbubblestability.However,thereisnoreportedevidencetosuggestthatthestarchgranulesinteractwithairbubblestrapped in thebatter.The reason for thismay be that the starchgranules have arelativelysmallsurfaceareacomparedwiththatofthegasbubbles,especiallywhenthebubblesbegintoexpand.However,withthemechanismofstabilizationbysolidparticles in mind, the potential contribution of starch granules toward interfacialstabilitycannotberuledout.

. aPPlICatIonofenzyMesto generatesurfaCe-aCtIveMaterIals

Inadditiontonaturalorsyntheticsurface-activeagents,highlyactivematerialscanalsobecreatedin situbytheactionofspecificenzymesonsubstratesthatarepresentinrawmaterials,suchasflour,egg,orshortenings.Suchenzymeshavethepoten-tialtoreplaceaddedemulsifiers.Thisisofconsiderableimportanceintermsofthehealthimageofaproduct,becauseenzymeshavenofunctioninthefinalproductanddonothavetobedeclaredonthepackaging.Thishasledtotheapplicationofenzymestoproducetherequiredsurface-activematerialsin situ.Thereareanumberofesterhydrolasesthatcanmodifythechemicalstructureofphospholipids—namely,phospholipasesA1,A2,C,andD.PhopholipaseAhasbeenusedbythefoodindustryformanyyearstoimprovethefunctionalityofeggyolkbybreakingdownthelipidcomplexes.Lipaseenzymesarepresentincerealsinsmallconcentrationsandareknowntoproducefattyacidsinfloursstoredforlongperiods.Theactionoflipaseistocleavethebondbetweenthefattyacidestersandglycerol.Thenetresultistheproductionofamixtureoffattyacidsandthesurface-activemonoglycerides,whichitisclaimed,maybeusedtoreplacemonoglyceridesusuallyaddedasaningredient.

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Cake Emulsions

Thefunctionalityofthemonoglyceridesproducedwouldbedependentonthesourceofthetriglycerideactingasthesubstrate.Saturatedfattyacidswith14to18carbonatomsintheirchainsarethemosteffectiveantistalingmonoglycerides.

However,itisnotcleariftherequiredconcentrationlevelsofemulsifierscouldbeproducedbyaddedlipase,orwhetherthelargeamountsoffattyacidsproducedatthesametimewouldbedetrimentalorbeneficialtothebakingprocess.

Continuingprogressinbiotechnologyhasproducedanewgenerationoflipasesthatactonthenonpolartriglyceridesandpolarlipidsnaturallypresentinwheatflour.Wheatflourcontains2to3%lipidmaterialconsistingofbothpolarandnonpolarfrac-tions.However,alargeproportionofthislipidisfoundinthestarchgranularstructureandhence isnot availableas substrate for lipaseaction.Thenonstarch lipid formsabout1.6%oftheflourweight,andoutofthisabout0.6%iscomposedofthefunction-allyimportantpolarfraction.Examplesofthepolarlipidsfoundinflourincludethephospholipidlecithinandthegalactolipiddigalactosyldiglyceride.Actionofthenewlipaseontriglyceridemoleculeswouldbeexpectedtoproducemono-anddiglyceridesaswellasfreefattyacids.Theseby-productsofenzymeactionaresimilartothosegeneratedbythetraditional1,3specificlipase.However,itistheactiononthepolarlipidswhichisofinterestintermsofincreasingthesurfaceactivityofthesematerials.Theactionofthenewlipaseonlecithincleavesoneofthefattyacylchainstoproducelysolecithin,amoresurface-activematerialcomparedtotheoriginalsubstrate.Like-wise,thecleavageofanacylchainfromadiglyceridedigalactosylmoleculeproducesthemoresurface-activedigalactosylmonoglyceride.Theutilityofthisenzymetopro-ducesurface-activematerialsin situwasinvestigatedinthemanufactureofhigh-ratiocakesusingarangeofflours.Initially,theperformanceoftheenzymewasassessedbyitseffectonthebatterdensitywithmixingtime.Mixingtimetoachievethetargetbatterdensity(0.72g/ml)wasreducedbyaminimumof24%at90ppmadditionoftheenzymeforoneflourandupto35%foranotherflourbasedonthemixingtimewithnoenzymeadded.Twootherfloursexaminedhadmixingtimereducedtointermediatevaluesbetweenthetwoextremes.Theuseofemulsifierstoreducemixingtimeofbat-tersiswellrecognizedinthecake-makingindustry,andthesameeffectobservedwiththeuseofthenewlipasewouldsuggesttheproductionofsurface-activematerialsbytheenzyme.Fundamentalstudieswithcakebattersuggestedthepresenceofsurface-activematerials.Thesematerialsloweredthesurfacetensionandthesurfaceviscosity(Table4.1),probablybydisplacingtheproteincomplexeswithmono-acyllipidssuchas fattyacids, lysolecithin, anddigalactosylmonoglycerides (GuyandSahi,2006).Thepresenceofthesematerialswasconfirmedbyanalysisoffreefattyacidsandanincreaseinamylose–lipidcomplexesfoundinthebakedproduct.

Enzymeadditionalsoincreasedbatterviscosityinproportiontotheamountofenzymeused,and thiswouldbenefit thestabilizationof thebubbles in thebatteraftermixingandduringtheirexpansioninthebakingprocess.Itisthoughtthatthesurface-activematerialsmayhavewetted-out theproteins andhelped to increasetheirhydrationvolumes,becausetheincreasesinviscositywerelostathighshearlevelsinthebatter.Initialbakingtrialswiththreeheat-treatedfloursusedtomanu-facturehigh-ratiocakesshowedimmediatebenefitsinincreasedcakevolume(Fig-ure4.2).Intotal,thisimprovementwasfoundwithsixdifferentflours,fromthreedifferentcommercialmillingcompanies(GuyandSahi,2006).Analysisofthecake

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crumbstructuresuggestedthatthecellsweremorestable,becausetheyweregener-allysimilarinnumberinthecakes,buthadincreasedinsizetogiveextravolume(Figure4.3).

Enzymaticmodificationofproteinshasalsobeenattemptedinordertoimprovetheir emulsifying and foaming properties. This usually involves incorporation ofsubstituentgroupsintotheproteinstructureinordertoimprovethesolubility.Forexample,thesulfhydralgroupsofproteinshavebeenmodifiedtoimprovesolubilityandotherfunctionalproperties(RegensteinandRegenstein,1984).Enzymeshavebeenusedtomodifygelatinproteinsproducingamixtureofpolypeptidesknownasenzymaticallymodifiedgelatin-6(EMG-6)andEMG-12.Breadbakingtrialsdem-onstratedthatEMG-12couldimproveloafvolume(AraiandWatanabe,1988),butnotrialswereperformedoncakesystems.

taBle.

effectofnewlipaseonsurfacePropertiesoftheaqueousPhasesofhigh-ratioCakeBattersat°C

sample surfacetension(mn/m) surfaceviscositya(unm.s/m)

Water 72.5±0.3

Controlbatter 31.7±0.2 118±10

Batterwith60ppmlipase 31.1±0.1 80±5

Batterwith90ppmlipase 30.1±0.2 38±5a Surfaceviscosityachievedafter30min.

0 60 90Lipopan level, ppm

900

850

800

750

700

650

600

Volu

me o

f cak

e, m

l

Flour 1 Flour 3 Flour 4

fIgure. Effectofnewlipaseadditiononthevolumeofhigh-ratiocakes.

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Cake Emulsions

. ConClusIon

Thischapterpresentedanoverviewoftheinterfacialpropertiesrelevanttothefor-mationandthestabilityofemulsionsandfoamsinrelationtocakeemulsions.Theroleofemulsifiersandotherkeyrecipeingredientsandtheircomponentsinrelationto influencing interfacial properties was discussed. The interactions of emulsifiermolecules at air–water andoil–water interfaces are crucial to stabilizing thedis-persedairandfatphasesincakebatters.Emulsifierinteractionsatamolecularlevelwithothercomponentssuchasfatandproteinshavebeenshowntobeimportanttofoamandemulsionstability.Chemicallysynthesizedemulsifiershaveplayedakeyroleinthemanufactureofcakesformanyyears.However,thetrendofconsumerdemandfornaturalingredientshasledtoalternativewaysofproducingemulsifiers.Theuseofmethodstoproducesurface-activematerialsin situwiththeapplicationofenzymesislikelytoincrease.Initially,thismayservetopartiallyreplacechemicallysynthesizedemulsifiers,withfullreplacementpossibleonlyinrecipeformulationsthatdependonrelativelylowlevelsofaddedemulsifiers.However,developmentsinbiotechnologymayleadtoenzymesthatcangenerategreateramountsofsurface-activematerialsin situ,whichalongwithchangesinrecipeformulationorprocess-ingmethodsmayleadtofullreplacementofchemicallysynthesizedemulsifiers.

0 60 90Lipopan level, ppm

900

850

800

750

700

650

600

Volu

me o

f cak

e, m

l

Flour 1 Flour 3 Flour 4

fIgure. Functionality of new lipase in high-ratio cakes. (Courtesy of Campden &ChorleywoodFoodRA,ChippingCampden,UK.)

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suggestedfurtherreadIng

Bennion,E.B.andG.S.T.Bamford.1997. In:Technology of Cake Making,Ed.A.J.Bent,BlackieAcademic&Professional:Glasgow.

Friberg,S.,K.Larsson, and J.Sjoblom (Eds.). 2003.Food Emulsions (Food Science and Technology),4thed.CRCPress:BocaRaton,FL.

Shaw,D.J.1980.Introduction to Colloid and Surface Chemistry,3rded.Butterworth-Heine-mann:Oxford.

Whitehurst,R.J.(Ed.).2004.Emulsifiers in Food Technology.Blackwell:Oxford.

referenCesAmbwani,D.S.andT.FortJr.1979.Pendantdroptechniquesformeasuringliquidboundary

tensions.In:Surface and Colloids Science,vol.II,Eds.R.J.GoodandR.R.Stronberg,Plenum:NewYork,93–119.

Arai,S.andW.Watanabe.1988.Emulsifyingandfoamingpropertiesofenzymaticallymodi-fiedproteins.In:Advances in Food Emulsion and Foams,Eds.E.DickinsonandG.Stainsby,ElsevierAppliedScience:NewYork,189–220.

Bergenstahl,B.A.andP.M.Claesson.1990.Surfaceforcesinemulsions.In:Food Emulsions,Eds.K.LarssonandS.E.Friberg,MarcelDekker:NewYork,41–96.

Brooker,B.E.1993.Thestabilisationofairincakebatters—Theroleoffat.Food Structure12:285–296.

Carlin,G.T.1944.Amicroscopicstudyofthebehaviouroffatsincakebatters.Cereal Chem-istry21:189–199.

Clark,D.C.,M.Coke,A.R.Mackie,A.C.Pinder,andD.R.Wilson.1990.Moleculardiffusionandthicknessmeasurementsofprotein-stabilisedthinliquidfilms.Journal of Colloid Interface Science138:207–218.

Clark,D.C.,A.R.Mackie,P.J.Wilde,andD.R.Wilson.1994.Differencesinthestructureanddynamicsoftheadsorbedlayersinprotein-stabilisedmodelfoamsandemulsions.Faraday Discussions98:253–262.

Guy,R.C.E.andS.S.Sahi.2006.Applicationsofalipaseincakemanufacture.Journal of the Science of Food and Agriculture.SpecialIssue:EnzymesinGrainProcessing86(11):1679–1687.

Hoerr,C.W.1960.Morphologyoffats,oilsandshortenings.Journal of American Oil Chem-ists Society37:539–546.

Izydorczyk,M.,C.G.Biliaderis,andW.Bushuk.1991.Physicalpropertiesofwater-solublepentosansfromdifferentwheatvarieties.Cereal Chemistry68(2):145–150.

Knightly,W.H.1988.Surfactantsinbakedfoods:Currentpracticeandfuturetrends,Cereal Foods World,33, 405–412.

Krog,N.andK.Larsson.1968.Phasebehaviourandrheologicalpropertiesofaqueoussys-temsofindustrialdistilledmonoglycerides.Chemistry Physics Lipids2:129–143.

Montgomery,R.andF.Smith.1956.Hemicelluloses inflour.Journal of Agricultural and Food Chemistry47:716–720.

Prins,A.1988.Principlesoffoamstability.In:Advances in Food Emulsions and Foams,Eds.E.DickinsonandG.Stainsby,ElsevierAppliedScience:London,91–122.

Regenstein,J.M.andC.E.Regenstein.1984.Sulphydralchemistry.In:Food Protein Chem-istry,AcademicPress:London,p83.

Sahi,S.S.1994.Interfacialpropertiesoftheaqueousphasesofwheatflourdoughs.Journal of Cereal Science20:119–127.

Shaw,D.J.1980.Liquid–gasandliquid–liquidinterfaces.In:Introduction to Colloid Chem-istry,3rded.Butterworths:London,pp.60–90.

Shepherd,I.S.andR.W.Yoell.1976.Chapter5:CakeEmulsions.In:Food Emulsions,EdS.Friberg,MarcelDekker:NewYork,pp/270–274..

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5 Cake Batter Rheology

Serpil Sahin

Contents

5.1 Introduction...................................................................................................995.2 RheologicalMethods.................................................................................. 1005.3 FactorsAffectingRheologyofCakeBatters.............................................. 102

5.3.1 EffectsofIngredients....................................................................... 1025.3.1.1 Flour................................................................................... 1025.3.1.2 FatandFatReplacer........................................................... 1045.3.1.3 Emulsifiers.......................................................................... 1075.3.1.4 Sugar................................................................................... 1105.3.1.5 Hydrocolloids..................................................................... 1105.3.1.6 Egg...................................................................................... 113

5.3.2 EffectsofMixingandDosing......................................................... 1135.3.3 EffectofTemperature...................................................................... 115

5.4 Conclusıon................................................................................................... 117References.............................................................................................................. 117

. IntroduCtIon

Understandingtherheologicalcharacteristicsoffoodmaterialsisnecessaryforplantandproductdesign.Itisimportanttodeterminetherheologicalpropertiesofcakebatterbecausethequalityattributesofcakessuchasvolumeandtexturecanbecor-relatedwithrheologicalpropertiesofbatter.

Thebasic ingredients incakebattersareflour, fat,egg,milk,sugar,andsalt.Flour,eggwhite,milksolids,andsaltareused to toughen thecake,whilesugar,fat,andeggyolkareusedtotenderizethecake.Cakebattercanbeconsideredasacomplexoil-in-wateremulsionwithacontinuousaqueusphasecontainingdissolvedorsuspendeddryingredientssuchassugar,flour,salt,andbakingpowder.Theoilphaseremainsdispersedinclumpsthroughoutthecontinuousorliquidphaseanddoesnotbecomepartoftheliquidphase(Painter,1981).Theinteractionofingredi-entsandstructuredevelopmentoccursduringthemixingandbakingstages.

Theincorporationofaircellsinthesystemduringmixinggivesrisetoafoam.It is important to obtain a large number of small cells to provide higher volume(Handlemanetal.,1961).Duringbaking,anaeratedemulsionofcakebatteriscon-vertedtoasemisolidporous,softstructuremainlyduetostarchgelatinization,pro-teincoagulation,andcarbondioxidegasproducedfromchemicalsdissolvedinthebatter,airocclusionduringmixing,andtheinteractionamongtheingredients.

Viscosityofcakebatteristhecontrollingfactorforthefinalcakevolume.Therateofbubbleriseduetobuoyancyforceisinverselyproportionaltotheviscosity.

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Inthepresenceofless-viscousbatter,carbondioxideevolves,andthewatervaporproducedmightnotbetrappedinthesystemduringbaking,thusresultingincakeswithlowvolume.Highercakebatterviscositieshelptoretainmoreairbubblesinthebatterandretardtheriseofbubblestothesurface.Inaddition,thevelocitygradientinthebatterduringbakinginducesconvectioncurrentatanygiventimedependingonitsviscosity,withlowerbatterviscosityresultinginmoreconvectionflow(FryeandSetser,1991).Itisalsoknownthathigherbatterviscositypreventstheentrappedairfromcoalescingduetodrainageofsurroundingbatterduringbakingandreducesshrinkage. In fact, there is an optimum viscosity of cake batter to achieve cakeswithhighvolume.Iftheviscosityofthebatteristoolow,battercannotholdtheairbubblesinsideandcakescollapseintheoven.Althoughahighlyviscousbattercanholdtheairbubblesinside,theexpansionofthisbatterisrestrictedbecauseofitshighviscosity(SahiandAlava,2003).

Therearemanystudiesintheliteratureinwhichrheologicalpropertiesofcakebatterarecorrelatedwiththequalityofcakes(ValiandChoudhary,1990;SahiandAlava,2003;Lakshminarayanetal.,2006).Batterswith lowspecificgravityandhighviscosityproducedcakeswithhighervolumes(ValiandChoudhary,1990).Theincreaseinbatterdensity(decreaseinaircontentincorporatedinbatter)decreasedthestorage(elastic)and loss (viscous)moduliofcakebatterandalso thespecificvolumeofcake(SahiandAlava,2003).Batterwithlowviscosityproducedcakewithlowvolumeandfirmertexture(Lakshminarayanetal.,2006).

Inthischapter,rheologicalmethodsusedincakebatterwillbeexplainedbriefly,andthentheparametersaffectingtherheologyofcakebatterwillbesummarized.

. rheologICalMethods

Foodmaterialsexhibitflow,deformation,orbothunderexternalforce.Rheologyisthesciencedealingwiththedescriptionofthemechanicalpropertiesoffoodmateri-alsunderwell-defineddeformationconditions.Basicrheologyconceptscanbeclas-sifiedintoviscousflow,elasticdeformation,andviscoelasticity.

Non-Newtonianshearthinning(pseudoplastic)behaviorwasobservedincakebattershavingdifferentformulations,andtherheologicalbehaviorofcakebatterswaswelldescribedbythepowerlawmodel(Baixaulietal.,2007;Gujraletal.,2003;Sakiyanetal.,2004;ShepherdandYoell,1976;Turabietal.,2007).Thepowerlawmodel(Ostwald–deWaeleequation)isexpressedas

τ γyzz

n

yznk

dvdy

k=

= ( )

(5.1)

wherekistheconsistencycoefficient(Pa⋅sn),nistheflowbehaviorindex(n <1forshearthinningfluids),τyzistheshearstress(N/m2),and γyz istheshearrate(1/s).

Baiketal.(2000)observedthattheflowbehaviorofcakebattershavingdiffer-ent formulationswaspseudoplasticwithayieldstress,and theshearstress–shearraterelationshipwasfittedwellwiththeCassonmodel:

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Cake Batter Rheology 0

( ) . . .τ τ γyz c yzk0 5

00 5 0 5

=( ) + ( ) (5.2)

whereτ0istheCassonyieldstress(N/m2),Kcistheconsistencycoefficent(Pa·s)0.5.Inricecakebatters,bothpowerlawmodelandCassonmodelwerefoundtobe

suitabletoexplaintheirrheologicalbehavior(Turabietal.,2007).IdealelasticsolidsdisplayHookeanbehavior.Whenaforceisappliedtoasolid

materialhavingthisbehavior,astraight-linerelationshipbetweenstressandstrainwasobserved.ThisrelationshipisknownasHooke’sLaw:

τ γ= G (5.3)

whereG istheshearmodulus(N/m2), τ isshearstress(N/m2),and γ isshearstrain.Cakebatter,likemanycomplexstructuredfoodmaterials,displaysbothviscous

andelasticpropertiesandisknownasaviscoelasticmaterial.Differentmethods,suchasthedynamic(oscillatory)test,creeprecoverytest,stressrelaxation,andsoforth, canbeused to study theviscoelasticbehaviorof foodmaterial (SahinandSumnu,2006).InthestudyofLeeetal.(2004),therheologicalpropertiesofcakebatterswerestudiedusinganoscillatorytest.

Inthestressrelaxationtest,stressismeasuredasafunctionoftimeasthemate-rial issubjectedtoaconstantstrain.Stress inviscoelasticsolidswilldecaytoanequilibriumstressσe,whichisgreaterthanzero,buttheresidualstressinviscoelas-ticliquidsiszero.

Ifaconstantloadisappliedtobiologicalmaterialsandifstressesarerelativelylarge,thematerialwillcontinuetodeformwithtime.Inthecreeprecoverytest,aninstantaneousconstantstressisappliedtothematerial,theresultingstrainismea-suredasafunctionoftime,calledcreep,andthenthestressisremovedwhilethestrainiscontinuedtoberecordedasafunctionoftime,calledrecovery.Idealelasticmaterials show complete recovery, and ideal viscous materials show no recoverywhentheappliedstressisremoved.Viscoelasticmaterialsareinbetween—thatis,theyshowpartialrecoveryaftertheremovalofstress.

Inthedynamic(oscillatory)test,materialissubjectedtodeformationorstressthatvariesharmonicallywithtime.Then,thetransmittedshearstressordeforma-tioninthesample,whichalsovariesharmonically,ismeasured,respectively(Fig-ure5.1).Storagemodulus(G′),whichishighforelasticmaterials,andlossmodulus(G′′),whichishighforviscousmaterials,aredefinedasfollows:

′ =G τ θγ

0

0

cos (5.4)

′ ′ =G τ θγ

0

0

sin (5.5)

where τ0 isshearstress(inputoroutput), γ0 isshearstrain(outputorinput),and θ istimelag(phaseshift).

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. faCtorsaffeCtIngrheologyofCaKeBatters

Rheologicalpropertiesoffluidfoodsarecomplexanddependonmanyfactorssuchascomposition,shearrate,durationofshearing,andpreviousthermalandshearhis-tories.Themost importantparametersaffectingtherheologicalpropertiesofcakebattersaretypeandconcentrationsoftheingredients,levelofairincorporation,andtemperature.Airincorporationisaffectedbytimeandspeedofmixing,designofthemixer,andsurfacetensionofthebatter.Studiesrelatedtotheeffectsofingredients(flour,fat,fatreplacer,emulsifiers,sugar,hydrocolloids,andegg),beatingandmixing,dosing,andtemperatureoncakebatterrheologyaresummarizedinthissection.

5.3.1 eFFeCTsoFinGredienTs

... flour

Flourisoneofthemostimportantingredientsaffectingtherheologicalpropertiesofcakebatterand,consequently,thequalityofcakes.Freshlymilledwheatflourhasapaleyellowcolorduetoitscarotenoidcontentandyieldsstickydough.Duringstorage,asaconsequenceofoxidativereactions,flourgraduallyturnswhite,andtherheologi-calpropertiesofdoughand,consequently,qualityofthebakedproductareimproved.Theageofflourisknowntoaffecttheviscosityofcakebatter.Shelkeetal.(1992)observedthatfreshlymilledflourshadlowwater-bindingcapacityandproducedbat-terswithlowviscosityatambienttemperatureandalsoduringheating.Batterviscos-ityatambienttemperatureandduringheatingincreasedwithflourage.Viscosityof

γ0

τ0

ShearStrain(Input)

ShearStress

(Output)

Phase Shift(Time Lag)

fIgure. Harmonicshearstressversusstrainforaviscoelasticmaterialindynamictest.

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battersatambienttemperaturesincreasedasafunctionofpostmillingtime.However,theageofwheatatmillingdidnotsignificantlyaffectbatterviscosity.

In making cakes, doughnuts, cookies, crakers, wafers, pretzels, and similarproducts,softwheatflourisused.Softwheatflourhaslowglutencontent,lowwater-absorptioncapacity, and lowgranulation size. It is commonlychlorinated for theproductionofcakes.Chlorinationisusuallydonewithchlorinegasandcanbemoni-toredbyadropinpHofflour.

Chlorinetreatmentofsoftwheatfloursimprovescakevolumeandproducesastiffer,moreresilientcrumb(Donelsonetal.,2000).Chlorinetreatmentofcakeflouris functionallybeneficial to theproductionofhigh-ratiocakes.White layercakesbakedusinguntreatedflourareunsatisfactoryinvolume,contour,crumbgrain,andtexture.Chlorine-treatedflourproducescakecrumbwithadrier,lessstickymouth-feel(KissellandYamazaki,1979).

Starch,lipid,andproteinsareallaffectedbychlorination.Theoxidativedepo-lymerizationofstarchwhichincreasesthewater-bindingcapacityofstarchisoneof the important changes that occur during chlorination (Huang et al., 1982). Attemperatures90°Candabove,swellingpowerandsolubilityofhighstarchfractionincreased as a result of chlorination (Huang et al., 1982).Water activitiesofbat-tersmadewithchlorinatedoruntreatedflourswerethesameuntilthetemperaturereached80°C.Batterscontainingchlorinatedflourhadhigherwateractivityat80°C.Storagemodulus(G′)increasedinthecaseofchlorine-treatedbatter,butitdecreasedinthecaseofuntreatedsamplebetween90and100ºC(Ngoetal.,1985).Thebatterpreparedwithchlorine-treatedflourhadamuchhigherlossmodulus(G′′)thandidthebattermadefromuntreatedflour.Alterationofstarchacceleratesthethickeningoftheviscosityofthebatterwhichresultsinhighervolume(GainesandDonelson,1982).Shelkeetal.(1992)alsoobservedthatthechlorinatedflourhadhigherviscos-itythanuntreatedflour.Freshlymilledfloursproducedbatterswithlowminimumviscosity,andminimumviscosityoffloursincreasedduringaging.Minimumvis-cosityofbatterduringheatingisanimportantpropertybecauseitreflectstheabilityofthebattertoretaingasbubblesandtoresistsettlingofstarch.

Chlorinationaffectsthehydrogenbondsoftheproteinsandcausesgreatersol-ubilityof the softwheatproteins (Kissell,1971).Hydrophobicityofproteinsalsoincreases with chlorination (Sinha et al., 1997). Chlorine treatment enhances thegel-formingproperties(Frazieretal.,1974).Chlorinationalsochangesthehexane-extractableflourlipidswhichresultsinhigherbatterexpansionduringbaking(Kis-selletal.,1979).

GainesandDonelson(1982)studiedtheeffectsofbleachingofflourandbatterliquidlevelsoncakebatterviscosityandexpansionduringheating.Floursobtainedfromtwodifferentvarietiesofwheatwereusedinthisstudy.Apparentviscositiesofthecakebatterspreparedusingdifferentwaterlevelsweremeasuredwithamodi-fiedviscographbetween20and100ºCcontinuously.Flourbleachingincreasedbat-terexpansioninbothflour types.Therewasanoptimumwater levelbetweentheextremeliquidlevelsgivingmaximumcakeexpansionforbothflourtypes.Bleachedfloursattheoptimumliquidlevelsachievedhigherpastingviscositiesmorerapidlythanunbleachedflours.Fasterpastingmaycontributetothestabilityandreducedshrinkageofbleached-flourcakesoncooling(KissellandYamazaki,1979).There

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wasalsoanoptimumviscosityforcakeexpansion.Thatis,cakeexpansionincreaseduptoacertainlevelandthenstartedtodecreaseasbatterviscosityincreased.

Ratswere fedwith cakesmadewith chlorine-treatedflour at ingestion levelsequivalenttotheconsumptionofcakeinthehumandietinordertotestthesafetyofconsumptionofchlorinatedflour,andnoadversereactionwasobserved(Danielsetal.,1963).However,athigheringestionlevels,reducedgrowthrate,increasedliver,kidney,andheartweights,andreductioninovaryweight(amongfemalemice)wereobserved(Cunninghametal.,1977;Ginocchioetal.,1983).Therefore,productionofbakedproductsusinguntreatedwheatflourisofgreatconcernforsafetyaspects,andithasbeenremovedfromthepermittedlistoffoodingredientsintheEuropeanUnion for cake manufacture. However, in order to produce cakes having similarpropertiestothoseproducedusingchlorine-treatedflour,someadditionalingredi-entsmaybeaddedtountreatedflourorheatedflourmaybeusedasanalternativetochlorine-treatedflour.Improvedcakevolumeandcontourwereobservedwhenuntreatedflour–starchblendwasused(JohnsonandHoseney,1979).Whenacer-tainamountof(12to43%dependingonthetypeoftheuntreatedflour) starchwasaddedtotheuntreatedflour,itwaspossibletoobtainpastingcurveareasequivalentto those obtained in the case of chlorine-treated flours in Rapid Visco Analyzer(Donelsonetal.,2000).Starchactsasawatersinkduringbaking,contributingtothesettingofthestructureofthecakeduringbaking.

Heat-treated flour has been introduced as an alternative to chlorinated flour.Heattreatmentimprovesflourperformanceasinthecaseofchlorinetreatment.Heattreatment of flour denatures wheat proteins and reduces their solubility in water.Therefore, batters made from heat-treated flour have higher viscosity comparedwithbattersmadewithuntreatedflour,andhigherviscosityhelpstotrapandsub-divideairinthebatterduringmixing.Thetemperatureofthefirstriseofviscositydecreaseswithheat-treatedflourinBrabenderAmylographanalysis(Seguchi,1990).Heat treatment may split some of the linkages of starch amylose or amylopectinchains resulting in lowering theoptimumviscosityofwheatflour.Thomasson etal. (1995) added xanthan gum, L-cysteine, or hydrogen peroxide plus peroxidaseenzymetoheat-treatedflourandobtainedcakeshavingcomparablevolumewiththeonesproducedusingchlorine-treatedflour.

... fatandfatreplacer

Oils are refined and may be partially hydrogenated. Cake margarines and short-eningsareformulatedfromblendsofprocessedoilsandfats.Incakemargarines,the aqueous phase contains skim milk. Shortening normally contains a mixtureofglycerideshavingwidelydifferentmeltingpoints.Inacakesystem,shorteningservesthreemajorfunctions:toentrapairduringthecreamingprocess,tophysicallyinterferewiththecontinuityofstarchandproteinparticles,andtoemulsifytheliq-uidinformulation.Thus,shorteningaffectsthetendernessandmoisturecontentofthecake.Theadditionoflipidimprovesairincorporationandfoamstabilitywhichaffectbakingquality.Inaddition,fatsandemulsifiersareknowntodelaygelatiniza-tionbydelayingthetransportofwaterintothestarchgranuleduetotheformationofcomplexesbetweenthelipidandamyloseduringbaking(Larsson,1980).

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Thefunctionsoffatandoiloncakestructuredevelopmentaredifferent.Increaseinfatcontentincreasesshearmodulus,andincreaseinoilcontentdecreasesshearmodulus (Mizukoshi, 1985).The effect of different fats andoil on specificgrav-ityandviscosityofcakebattersand,consequently, thevolumeand tendernessofbakedcakewerestudiedbyValiandChoudhary(1990).Cakebatterwithmargarinecouldholdagreateramountofairandshowedlowspecificgravity,andthatwithoilandhydrogenatedfatshowedhighspecificgravity.Batterswithlowspecificgravityshowedhighviscosity,andtheyproducedcakeswithgreatervolumes.

Theeffectsofconcentrationoffat(0%,12.5%,25%,37.5%,50%)ontherheo-logicalpropertiesofcakebatterwerestudiedbySakiyanetal.(2004).Itwasfoundthatcakebatterwithdifferentfatconcentrationsexhibitedshearthinningandtime-independentbehavior.Theincreaseinfatcontentcausedadecreaseintheapparentviscosity.Figure5.2showsthedecreaseinapparentviscositywithappliedshearrateforcakebatterscontainingemulsifierblend,Lecigran®,anddifferentamountsoffat.Thistrendwasalsoobservedforthesamplescontainingnoemulsifier.Adecreaseinviscositywiththeincreaseinfatconcentrationwasanexpectedresult,becauseanincreasedamountoffatcausedmoreairentrapmentduringthecreamingprocess.Thereductionofapparentviscositywiththeadditionoffatwasalsoexplainedbythelubricationeffectofuniformlydispersedfatparticles.

Fataidsintheentrapmentofairduringmixingand,asaresult, improvestheleaveningofproduct.Fatalsoimpartsdesirableflavorandsoftertexturetothecakes.Althoughfatplaysanimportantroleinimprovingtheproductquality,thetrendistowardthereductionoffatforhealthconcerns.Severaltypesoffatreplacersareavail-ableinthemarketforthispurpose.Fatreplacerscanbecategorizedascarbohydrate

0 50 100 150 200 250

8

7

6

5

4

3

2

1

0

Shear rate (1/s)

Appa

rent

visc

osity

(Pa.

s)

fIgure. Effectsof fatcontentonapparentviscosityofcakebattercontainingLeci-gran®.(Linerepresentsthepowerlawmodel,0%fat,12.5%fat,25%fat,37.5%fat, * 50%fat.)(ReprintedfromSakiyan,O.,Sumnu,G.,Sahin,S.,andBayram,G.,European Food Research and Technology, 219, 635–638, 2004, Figure1. With permission fromSpringerScienceandBusinessMedia.)

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based (e.g., cellulose, dextrin, maltodextrin, fiber, gums, Oatrim, starch), proteinbased(e.g.,microparticulatedprotein,modifiedwheyprotein,Simplesse®),andlipidbased (e.g., caprenin, salatrim, olestra, emulsifiers, sucrose polyesters). DetailedinformationaboutthefunctionsoffatreplacerscanbefoundinChapter12.Rheo-logicalstudiesonfatreplacersincakebatterarelimitedtocarbohydrate-basedfatreplacers in literature.Carbohydrate-basedfat replacers, in thepresenceofwater,formasmoothgelresultinginlubricantandflowpropertiessimilartofats(Swansonetal.,1999).Theyincreaseviscosityandprovidecreamy,slipperymouthfeelsimilartothatoffat.

White layercakebatterscontainingstarch-based fat replacersandnoemulsi-fiershadhigherspecificgravitiesandlowerviscositiesbothatambienttemperatureandduringheating(Bathetal.,1992).Thelowviscosityofbattersmadeusingfatreplacersbothatambienttemperatureandduringheatingwasresponsiblefortheirrapidrateofheatinginelectricalresitanceovens.Cakeswithoutfatbecameflatandhadlowvolume.

Khouryiehetal.(2005)studiedtheeffectofincorporatingxanthangum,malto-dextrin, and sucralose tomakeno-sugar-addedand low-fatmuffinsandobservedthatremovingthefatfromthemuffinswasresponsiblefortheincreaseinhardnessandchewiness.Grigelmo-Miguel et al. (2001)useddietaryfiber as anoil substi-tuteinmuffinsandfoundthatitincreasedthehardnessandchewinessofmuffins.ShearerandDavies(2005)observedanincreaseinbatterviscosityandadecreaseinfirmnessandelasticityofthemuffinwiththeincreaseinflaxseedmealusedasasourceoffiber.Masoodietal.(2002)studiedtheeffectsofusingapplepomace atdifferentconcentrationsandparticlesizesasasourceofdietaryfiberonthequalityof cakes.Batterviscosity increasedwith increasingconcentrationanddecreasingparticlesizeofpomace.

Lakshminarayan et al. (2006) investigated the effects of fat replacement bymaltodextrinoncakebatterviscosityandthequalityofthebakedproduct.Thevis-cosityofbatterwasreducedsignificantlywhenfatwasreplacedwithequalquan-tities of maltodextrin. Batter with low viscosity produced cake with low volumeandfirmertexture.Whentheamountofreplacementwaslowerintheformulation,viscosityofthebatterwasrelativelyhigherandqualityoftheresultantcakeswasrelativelybetter.

Kimetal.(2001)studiedtheeffectsofreplacementofshorteningwithmalto-dextrin,amylodextrin,octenylsuccinylatedamylodextrin,ormixturesof themon yellowlayercakebatterandbakedproductproperties.Thespecificgravityandvis-cosityofcakebatterandvolumeindexofbakedcakeweresignificantlyreducedbymaltodextrin,butthecakewithamylodextrinandoctenylsuccinylatedamylodextrinshowedhighervolumeindexthanthecontrolcakecontainingshortening.

Thesolublefiberinoatbran,β-glucan,isawell-recognizednutraceutical.Nutrimoatbran,whichisahydrocolloidobtainedfromoats,providesaviablesourceofβ-glucanforuseinthefoodindustry.Flaxseedisagoodsourceofomega-3fattyacids,α-linoleicacid,dietaryfiber,andlignanswhichhavebeneficialhealtheffects.TheeffectsofreplacementofshorteningwithNutrimoatbranandflaxseedpowderonthephysicalandrheologicalpropertiesofcakeswereinvestigated(Leeetal.,2004).Cakebatters showed shear thinningbehavior.Slightlyhigher shearviscosity and

52748.indb 106 2/6/08 2:25:41 PM



oscillatorystorageandlossmoduli wereobservedinbatterscontainingNutrimoatbran than in thecontrol,and thereplacementofshorteningwithflaxseedpowderreducedviscosityandoscillatorystorageandlossmoduli ofthecontrolcakebatter.Cakeshavingsimilarqualityparameterswith thecontrolcakecouldbeobtainedwithupto40%fatreplacement.

Inanotherstudy,theeffectsof‚replacementofshorteningwith20%,40%,and60%byweightofOatrim(oatβ-glucanamylodextrin)onthephysicalandrheologi-calpropertiesofcakeswereinvestigated(Leeetal.,2005).ThespecificgravityofthecakebattersincreasedasmoreshorteningwasreplacedwiththeOatrim,andnosignificanteffectwasobservedinthecaseof20%Oatrimcontent.Shearthinningbehaviorwasobservedinalltypesofbatters.Thecontrolcakehadthehighestvis-cosity,andanincreaseinthelevelsofshorteningreplacementwithOatrimcausedareductioninviscosityofcakebatters.Themeansizeoftheairbubbles,1.5×10−9m2,wasnotsignificantlyaffected,butthenumberofairbubblesincorporatedinthesamplewassignificantlyaffectedfromthereplacementofshortening.

The cake batters containing more Oatrim displayed a higher gelatinizationtemperatureduetoamylodextrinsintheOatrimandtheyhavelowervolume.Therheologicalpropertiesofthecakeswerestudiedduringheatingtomimicthebakingprocess.Theoscillatoryshearstoragemodulidecreaseduponinitialheating,thenincreasedduetostarchgelatinization,andfinallyreachedaplateauvaluethatvariedbasedonthesamplecomposition.IncreasedreplacementofshorteningwithOatrimresultedinhigherobservedoscillatoryshearstoragemoduli.Correlationsbetweenoscillatory shear storagemoduli and thedifferential scanningcalorimetry (DSC)thermogramswereinvestigated.

... emulsifiers

Emulsifiersarecommonlyusedinthebakingindustry.Theyhavetheabilitytopro-videthenecessaryaerationandgasbubblestabilityduringtheprocess.Anemulsi-fierreducestheinterfacialtensionbetweenoilandwaterandthereforefacilitatesthedisruptionofemulsiondropletsduringhomogenization.Theemulsifieradsorbsonthesurfacesofemulsiondropletstoformaprotectivecoatingthatpreventsthedrop-letsfromaggregatingwitheachother.Emulsifiersaidintheincorporationofairanddispersetheshorteninginsmallerparticlestogivethemainnumberofavailableaircells(Painter,1981).Airincorporation,volume,anddispersionofingredientswereaffectedbytheamountandtypeofemulsifier(Clokeetal.,1984).

Theadditionoflipid-likeemulsifierstocakesystemsaffectsboththeinterfacialand bulk properties of the batter. The effects of two different types of emulsifi-ers(glycerylmonostearate[GMS]andpolyglycerolester[PGE])onthestructureofspongebatterswerestudiedbySahiandAlava(2003).Theadditionofanemulsifierimprovedwaterbindinganddecreasedthefluidityofthebatter.Adynamicoscilla-torytestwasperformedtodeterminetheviscoelasticpropertiesofthebatters,anditwasobservedthattheadditionofanemulsifierresultedinanincreaseinelasticandviscousmoduli(Table5.1). Thedecreaseinbatterdensity(increaseinaircon-tentincorporatedinbatter)increasedtheviscousandelasticmoduliofcakebatterand also the specific volumeof the cake.Bubbles in batter samples immediately

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aftermixingwereimagedusinganopticalmicroscopeandacharge-coupleddevice(CCD)videocamera.Itwasobservedthattheadditionofanemulsifieratlowlevels(0.25%glycerylmonostearate)resultedinanincreaseinbubblesizeandheterogene-ityofbubbles.Increasingtheconcentrationoftheemulsifier(0.75%glycerylmono-stearate)providedsmallerbubbleswithmoreuniformbubblesizedistribution.

WhenGMSorsodiumsteroyllactate(SSL)wasusedasanemulsifierincakeformulationsinwhich25%fatwasreplacedwithmaltodextrin,theviscosityofcakebatterincreased(Lakshminarayanetal.,2006).However,adecreaseinthecakebat-terviscositywasobservedwhenfatreplacementwithmaltodextrinwas50%ormoreinthecaseofGMSadditionand75%inthecaseofSSLaddition(Figure5.3). SSLismorehydrophilicinnaturewithahydrophilic–lipophilicbalance(HLB)valueof10to12,anditwasmoreefficientinincreasingbatterviscosityinasystemwhenthefatlevelwasrelativelylow.GMSisamorelipophilicemulsifierwithanHLBvalueof3to4.Boydetal.(1972) observedthatoil-in-wateremulsionsweremorestablewhenemulsifierswithhigherHLBvalueswereused.

Thebest result is obtainedusing a blend of emulsifierswithdifferent hydro-philic–lipophilicpropertiesincomplexsystemslikecake.Theeffectsofdifferenttypesofemulsifierblends(Purawave®andLecigran®)ontherheologicalpropertiesofcakebatterhavebeenstudiedbySakiyanetal.(2004).Purawave(Puratos,Bel-gium) wascomposedoflecithin,soyprotein,mono-anddiglycerides,andvegetablegums.Lecigran(RicelandFoods,Arizona)wascomposedofoil-freesoybeanleci-thin,wheatflour,andhydrogenatedvegetableoil.Alltypesofcakebatterspreparedwithandwithoutemulsifiersexhibitedshearthinningandtime-independentbehav-ior.Experimentaldataprovidedagoodfitwiththepowerlawmodel.Theadditionofemulsifiercausedadecreaseintheapparentviscosity.Figure5.4showstheeffects

taBle.

resultsofdynamicoscillatoryMeasurementsofspongeCakeBattersatafrequencyof−hzemulsifiertype Concentration

(%batterwt)elasticModulus

(Pa)viscousModulus

(Pa)Phaseangle

(deg)

Control — 59±8 83±7 55±2

GMSa 0.25 115±16 142±11 51±2

GMS 0.75 487±60 392±57 39±3

GMS 1.50 1223±111 1037±217 40±4

PGEb 0.25 111±11 158±11 55±1

PGE 0.75 306±10 321±12.9 46±1

PGE 1.50 1047±65 878±70 40±2a Glycerylmonostearate.b Polyglycerolester.

Source:ReprintedfromSahi,S.S.andAlava,J.M., Journal of the Science of Food and Agriculture,83,1419–1429,2003.Copyright2003SocietyofChemicalIndustry.Reproducedwithpermis-sion.PermissionisgrantedbyJohnWiley&SonsLtd.OnbehalfoftheSCI.)

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ofemulsifiersonapparentviscosityofcakebatterhaving37.5%fatcontent.Effectsofemulsifiersonapparentviscosityofcakebattershavingdifferentfatconcentra-tionswerealsostudied,andthesametrendwasobservedinotherfatconcentrations.Adecreaseinviscositybyemulsifieradditionwasexplainedbytheincreaseinairentrapmentincakebatter,becausetheemulsifieraidsintheincorporationofairanddispersestheshorteninginsmallerparticlestogivethemainnumberofavailableairbubbles.

GuyandSahi(2006)studiedtheeffectofusinglipaseenzymeinsteadofemul-sifiers toimprovetheperformanceofhigh-ratiolayercakebattersmadewithheat-treated flours. It was reported that the commercial lipase, Lipopan F®, producesmonoacyllipidsfromlecithinandmono-anddigalactosyldiglyceridesfromthetri-glycerides.Asthelipaseconcentrationincreased,viscosityofthebatterincreased,which indicated the formationof surfactants.The surfactants producedby lipasemayhelp tohydratewheatproteinsand increase theirhydrodynamicvolumeandviscosityintheaqueousphase,aswellasstabilizetheairbubblesbyformingnewinterfacialmembranes(GuyandSahi,2006).Theadditionofenzymereducedthemixingtime,whichwasdefinedasthetimetakenforthebatterdensitytofalltoatargetvalueof0.85kg/Lwhilebeingmixed.

Gujraletal. (2003)studied theeffectof theadditionofsodiumlaurylsulfatewhichisananionicsurfactanttoeggalbumenduringthemixingstageontherheol-ogyofspongecakebatter.Therheologicalbehaviorwaswelldescribedbythepowerlawequation.Sodiumlaurylsulfateisusedtoimprovethefoamingpropertiesofegg

1715

1970 1940

1395

1650

1065

1360

830

1230

25 50 75

2500

2000

1500

1000

500

0

Fat reduction (%)

Cake

bat

ter v

iscos

ity (A

U)

MD MD+GMS MD+SSL

fIgure. Combinedeffectofmaltodextrin(MD)andemulsifiers(GMSandSSL)ontheviscosityofcakebatter.(ReprintedfromLakshminarayan,S.M.,Rathinam,V.,andKrish-naRau,L., Journal of the Science of Food and Agriculture,86,706–712,2006.Copyright2006SocietyofChemicalIndustry.Reproducedwithpermission.PermissionisgrantedbyJohnWiley&SonsLtd.onbehalfoftheSCI.)

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whites,marshmallows,andangelfoodcakemixes.Increasingtheconcentrationofsodiumlaurylsulfate loweredthespecificgravity,consistencycoefficient,andairbubblediameterofcakebatter.Theflowbehaviorindexincreasedsignificantlywithincreasingsodiumlaurylsulfateconcentration.

... sugar

Theadditionofsugarreducestheavailablewaterforstarchwhichaffectsrheologicalproperties,delaysstarchgelatinization,retardsstructuraldevelopment,andcontrolstheheat-settingtemperatureofeggproteinsduringbaking.Effectsofcakeingre-dientsontheshearmodulusofcakewerestudied,anditwasobservedthatsugardecreasedtheshearmodulusofadegassedbatter(Mizukoshi,1985).Batterviscos-ity at ambient temperature increased with an increase in the sugar concentration(Shelkeet al.,1990).An increase in sugar concentrationalso increased theonsettemperature.Sucrosewasmoreeffectiveascomparedtoglucoseandfructosewhentheonsettemperaturesofbatterscontainingdifferenttypesofsugarswerecomparedatthesameconcentration.

... hydrocolloids

Hydrocolloids are high-molecular-weight water-soluble polysaccharides used forviscosity control in many food systems. They are added to cake batters in smallamountstoimproveproductvolumeandtexture,toincreasemoistureretentiondur-ingbaking,andtopreventstaling.

100500 150 200 250

14

12

10

8

6

4

2

0

Appa

rent

visc

osity

(Pa.

s)

Shear rate (1/s)

fIgure. Effectsofemulsifiersonapparentviscosityofcakebatterat37.5%fatcontent.(Linerepresentsthepowerlawmodel,noemulsifier,Purawave®, Lecigran®.(ReprintedfromSakiyan,O.,Sumnu,G.,Sahin,S.,andBayram,G., European Food Research and Tech-nology, 219, 635–638, 2004,Figure4.Withpermission fromSpringerScience andBusinessMedia.)

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Cake Batter Rheology

Theeffectofxanthangumon the rheologyofwhite layercakebatterduringheatingwasstudiedusinganoscillatoryprobeviscometerinconjuctionwithelectricresistanceovenheating(MillerandHoseney,1993).Duringheating,batterviscositydecreasedtoaminimumandthenincreasedsharplytoamaximum.Theadditionofxanthantothebatterincreasedtheminimumandmaximumpoints.Batterviscosityatambienttemperatureandtheonsettemperatureofrapidincreaseinviscositywerenotsignificantlychangedwiththeadditionofxanthan.Theadditionofxanthangumimprovedthecakevolume.

Riceisoneofthemostfrequentlyusedcerealsasawheatsubstituteingluten-freebakedproductsforpatientswhohaveceliacdisease.However,somefoodaddi-tivessuchasstarches,gums,hydrocolloids,ordairyproductsshouldbeadded tothegluten-freebakedproductstoreducethepoorqualityduetothelackofglutenintheformulation.Turabietal.(2007)studiedtheeffectsofdifferentgums(xanthangum,guargum, locustbeangum,κ-carrageenan,hydroxy-propyl-methylcellulose[HPMC],xanthan–guargumblend,andxanthan–κ-carrageenangumblend)andanemulsifierblend,Purawave®(Puratos,Belgium),whichiscomposedoflecithin,soyprotein,mono-anddiglycerides,andvegetablegums,onrheologicalpropertiesofricecakebatterandqualitycharacteristicsofricecakesbakedinaninfrared–microwavecombinationoven.Inthisstudy,alltheformulationscontainingdifferentkindsofgumsandemulsifierblendshowedshear-thinningbehavior,whichmeansthatappar-entviscositydecreasedastheshearrateincreased.Theflowbehaviorofthericecakebatterswasdescribedbythepowerlawmodel.Table5.2showsthepowerlawmodelconstantsforalltheformulationscontainingdifferentkindsofgumsandemulsifierblend.Theflowbehaviorindexofbattersrangedfrom0.399to0.623.Battercontain-ingHPMCgumhadthelowestconsistencyindex.TheCassonmodelwasalsofoundtobeasuitablemodeltoexplaintherheologicalbehaviorofricecakebatters.ThecoefficientofdeterminationvaluesandthemodelconstantsfortheCassonmodelaregiveninTable5.2.ThelowestCassonyieldstresswasfoundforHPMC-containingbatters. Using the values of flow behavior index and consistency index, apparentviscositiesatashearrateof150s−1werecalculatedfordifferentformulationsfortheCassonmodelandaregiveninFigure5.5.Thehighestviscositieswereobtainedforbatterscontainingxanthanandxanthan–guarblend.Thisresultwasexplainedbythexanthan’sunique,rod-likeconformation,whichismoreresponsivetoshearthanarandom-coilconformation(UrlacherandNoble,1997).Thehigherviscosityvaluesofxanthan-containingbattersimprovedcakestructure,andthisresultedinhighervolumes.InthestudyofMillerandHoseney(1993),itwasalsoobservedthatxanthangumsignificantlyimprovedcakevolume.Synergisticinteractionbetweenxanthanandguargumresultedinhigherapparentviscosityascomparedtoothergums.Thissynergisticeffectwasnotobservedinthexanthan–κ-carrageenanblendwhichgavelowerapparentviscosityvalues(Figure5.5).Whenlocustbeangumwasusedintheformulations,itgavelowerapparentviscosityvaluesascomparedtotheguar-gum-containing batters.Thiswas explainedby thehighermolecularweightofguargum.HPMC-containingbattershadthelowestspecificgravityvaluesduetomoreair incorporationduringmixingand the lowestapparentviscosityvalues(Figure5.5).ThisresultedinthecollapseofHPMC-containingcakes.Theadditionofanemulsifierblendtothexanthan–guargumblendandthexanthan–carragenan

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gumblenddecreasedtheapparentviscosityofcakebattersignificantly(Figure5.5).Whenthefirmnessvaluesofcakeswereinvestigated,xanthan-andemulsifier-blend-containing cakeswere softer than those preparedwith other formulations,whichwerealsocorrelatedwithapparentviscosityresults.

Cakebatterscontainalargenumberofcomponentsthatcaninteractwitheachother.KimandWalker(1992)studiedtheinteractionsofstarches,sugars,andemul-sifiersinahigh-ratiocakemodelsystem.Modelcakeswerepreparedusingdifferent

taBle.

PowerlawandCassonModelConstantsforCakeBatterswithdifferentformulations

PowerlawModel CassonModel

formulation n K(Pa·sn) r2 zo(Pa) K(Pa·s)1/2 r2

Control 0.421 38.356 0.977 63.03 0.817 0.999

Xanthan 0.563 61.870 0.997 107.848 1.798 0.997

Guar 0.399 100.524 0.987 170.459 1.171 0.997

Xanthan+guar

0.552 69.580 0.994 126.293 1.811 0.992

Carrageenan 0.418 52.568 0.965 84.339 0.957 0.997

Locustbeangum

0.496 35.730 0.994 63.915 1.047 0.994

HPMC 0.596 12.898 0.991 20.025 0.952 0.999

Xanthan+carrageenan

0.541 53.091 0.986 86.902 1.569 1.000

Xanthan+emulsifier

0.610 46.980 0.997 78.711 1.871 0.997

Guar+emulsifier

0.399 111.830 0.991 213.131 1.149 0.949

Xanthan+guar+

emulsifier

0.545 59.377 0.997 114.833 1.595 0.981

Carrageenan+emulsifier

0.495 52.740 0.996 102.394 1.227 0.975

Locustbeangum+

emulsifier

0.513 35.710 0.997 65.398 1.113 0.993

HPMC+emulsifier

0.611 12.780 0.997 20.994 0.983 0.999

Xanthan+carrageenan+

emulsifier

0.623 29.520 0.997 47.967 1.557 0.999

Source:ReprintedfromTurabi,E.,Sumnu,G.,andSahin,S.,Food Hydrocolloids,22:305–312,2008.Copyright2008,withpermissionfromElsevier.

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typesofstarch(wheat,corn,orpotatostarch),sugar(lactoseordextrose,orreplace-mentof50%oflactoseordextrosewithsucrose),andemulsifiers(sucroseesterF-160orpolysorbate60).Thepototostarch,lactose,andpolysorbate60combinationproducedasignificantincreaseinbatterviscosity.Increaseinviscositytendedtoaidinairincorporation.

... egg

Eggproteinsarecritical for the structureof cakebatter.Eggwhiteproteinsmayenhancefoamstabilityandalsoacttocoagulateduringheatsetting.Lipoproteinsin egg yolk act as emulsifiers and assist in aeration and foaming (Shepherd andYoell,1976).Substitutionof10%ofeggwhiteinangelfoodcakebyfreeze-driedwheatwatersolubles,recoveredfromaby-productofagluten-starchwashingplant,decreasedbatterviscosity(Maziyadixonetal.,1994).Whippingtimeincreasedaspercentofsubstitutionincreased.

5.3.2 eFFeCTsoFmixinGanddosinG

Therheologicalpropertiesofbattersdependnotonlyonthetypesandconcentra-tionsof the ingredientsbutalsoon thebeatingandmixingprocess.Physicaland

Gum type

Appa

rent

visc

osity

(Pa.

s)0% emulsifier 3% emulsifier8

7

6

5

4

3

2

1

0x g x+g c lbg hpmc x+c control

abb

ded

a

c

g

f

g

g

h

h

d

ef

h

fIgure. Apparent viscosities (Pa.s) of formulations at 150 s−1 constant shear rateaccordingtotheCassonmodel.(x:xanthan,g:guar,x+g:xanthan+guar,c:carrageenan,lbg:locustbeangum,HPMC:hydroxyl-propyl-methylcellulose,x+c:xanthan+carrageenan,*barswithdifferentlettersaresignificantlydifferentp≤0.05.)(ReprintedfromTurabi,E.,Sumnu,G.,andSahin,S.,Food Hydrocolloids,22:315–312,2008.Copyright2008,withper-missionfromElsevier.)

52748.indb 113 2/6/08 2:25:50 PM



structural changes during aerated batter processing may alter batter performanceduringbakingormayalterthequalityofthefinalproduct.

Duringmixing,thesizeofbubblesdecreases.Providingnecessaryaerationbymeansofmixingandalsothestabilityofthegasbubblesduringthebakingprocessuntilthestructureissetareimportantfactorsinconsideringrheologicalpropertiesofcakebatters.Air incorporationduringmixing reduces thespecificgravityandapparentviscosityofbatter.

Viscoelasticpropertiesofmanuallydosedbattersaredifferentthanthoseofbat-ters passed through the automatic dosing unit. Baixauli et al. (2007) studied theeffectoftheuseofanautomaticdosingunitontherheologicalpropertiesofanaer-atedmuffinbatter.Flowandviscoelasticpropertiesofbattersdosedautomaticallyweremeasuredandcomparedwiththesepropertiesofthebattersdosedmanually.Inbothcases,shearthinningbehaviorwasobservedandthedatafittothepowerlawequationverywell.Theconsistency indexof thebattersdosedautomaticallywassignificantlyhigher,andtheflowindexwasnotaffectedfromthedosingtype.Passingthebatterthroughtheautomaticdosingunitproducedanincreaseinbothstoragemodulus(G′)andlossmodulus(G′′)at25°C(Figure5.6),buttherewasnosignificantdifferencebetweendifferentdosingtypesat85°C(Figure5.7).Itwasalsoobservedthatusinganautomaticdosingunitaffectsthemicrostructureofbatters.Battersshowedgreatercompactness,smallerfatglobules,andpartialdeformationinstarchgranuleswhenpassedthroughanautomaticdosingunit.

0.01 0.1 1 1010

100

1000

Frequency (Hz)

G,

G

(Pa)

fIgure. Mechanical spectra of manually dosed batter (circles) and batter that haspassedthroughtheautomaticdosingunit(triangles)at25°C.G′valuesarerepresentedbysolid symbols;G′′ are representedbyopen symbols.Shear stresswaveamplitude:0.1Pa.(Reprinted fromBaixauli,R.,Sanz,T.,Salvador,A.,andFiszman,S.M.,Food Hydrocol-loids,21,230–236,2007.Copyright2007,withpermissionfromElsevier.)

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5.3.3 eFFeCToFTemPeraTure

Rheologicalbehaviorsofcakebattersatdifferent temperatures(27to50°C)havebeenstudiedbyShepherdandYoell(1976).Non-Newtonianshearthinningbehaviorwasobserved.Adrasticchangeintheflowbehaviorindexwasobservedbetween35°Cand40°C.Thiswasexplainedbythemeltingoffatsurroundingtheairbubbleswhenthetemperaturewasabove35°Cwhichmadethebubblesmoremobileandabletomigratetotheaqueousphase.

Achange inbatter rheologyduringheating is very important. Generally, thebatterviscositydecreasesatthebeginningofheatingandthenstartstoincreaseatthestarchgelatinizationtemperature(Changetal.,1990).NgoandTaranto(1986)measuredviscoelasticpropertiesofcakebattersusingadynamic(oscillatory)test. Theyobservedthatthestoragemodulus(G′)andlossmodulus(G′′)increasedwhenthecakebattertemperatureincreasedfrom30to45°Candthengraduallydecreased,reachingaminimumvalueatatemperaturearound85°Cwhichvariedwithsugarcontent.Whenheatingwascontinued,G′andG′′increasedrapidlyuntilthebattertemperaturereached100ºC.ItwasexplainedthattheincreasesinG′andG′′whenthetemperatureincreasedfrom30to45°Cmightbecausedbygluten,milk,oreggproteininteractions,becausethistrendwasnotobservedinthecaseofthestarchpastesystem.

Thebakingprocessconsistsofthreestages—initial,middle,andfinalstages—accordingtoMizukoshi(1986).Theviscosityofthebatterdecreasedwithincreasing

0.001 0.01 0.1 1 10 10010

100

1000

Frequency (Hz)

G,

G

(Pa)

fIgure. Mechanical spectra of manually dosed batter (circles) and batter that haspassedthroughtheautomaticdosingunit(triangles)at85°C.G′valuesarerepresentedbysolidsymbols;G′′are representedbyopensymbols.Shearstresswaveamplitude:0.6Pa.(Reprinted fromBaixauli,R.,Sanz,T.,Salvador,A.,andFiszman,S.M.,Food Hydrocol-loids,21,230–236,2007.Copyright2007,withpermissionfromElsevier.)

52748.indb 115 2/6/08 2:25:54 PM



temperatureintheinitialstagesduetofoamdrainageandbubblecoalescence.Then,inthemiddlestagesofbaking,viscositystartedtoincreaseduetostarchgelatini-zation.Theincreasedshearmodulusofthecontinuousphasestabilizedthebubblestructureandreducedfoamdrainage(Mizukoshi,1983).Inthefinalbakingstage,starch gelatinization and protein coagulation were accelerated. The loss modulus(G′′)reacheditsmaximumvaluesasthefoamstructureofcakechangedfromdis-continuoustocontinuous.

Yasukawaetal.(1986)measuredthedynamicviscoeleasticpropertiesofcakebatter inamodelcakesystemduringbaking.Bothstoragemodulus(G′)andlossmodulus(G′′)startedtoincreaseatthegelatinizationtemperature.Initialstructuraldevelopmentwasduetostarchgelatinization.G′′reachedamaximumpointat88°C,whichisveryclosetothegasreleasetemperature.Thetemperatureatwhichbatterexpansionceasedcoincidedcloselywithitsgasreleasetemperatureandthetempera-tureatwhichG′′reacheditsmaximumvalue.

Major ingredients affect batter viscosity during heating in different ways.Effects of ingredients and additives (sugar type and concentration, shortening,eggwhite,hydrocolloids,emulsifier)onthedynamicsofcakebakingwerestudied(Shelkeetal.,1990).Batterviscositywasdeterminedusingacontinuousoscillatoryrodviscometerinconjuctionwithelectricresistanceovenheating.Batterviscositydecreasedasthetemperatureincreasedfromambientto60°Cduringtheearlyheat-ing,butviscosityincreasedsharplywithtemperatureastheheatingcontinuedabove60°Cduetothegelatinizationofstarch.Theonsettemperatureoftherapidviscosityincrease that is, starchgelatinizationwasnot affected significantlyby shorteninglevel.However,theincreaseintherateofviscositydecreasedwithincreasedshort-eninglevels,becauseshorteninglimitedthestarchswelling.Increasingshorteninglevelsdecreasedcakevolume.Batterscontainingsurfactantshadhigherviscosity.Nosignificanteffectontheonsettemperaturewasobservedwiththeadditionofsur-factant,buttherateofviscosityincreasedecreasedaftertheonset.Batterviscosityatambienttemperatureincreasedwithanincreaseinsugarconcentration.However,viscosityofbatterdecreasedwithanincreaseinsugarconcentrationduringheating.Atambienttemperature,notallofthesugarwasdissolved.Adecreaseinviscosityduringheatingwasexplainedwithdissolvingsugar.Theonsettemperatureincreasedasthesugarconcentrationincreased.Sucrosewasthemosteffectivesugarwhentheonsettemperaturesofbatterscontainingdifferenttypesofsugars(glucose,fructose,andsucrose)werecomparedatthesameconcentration.Theuseofeggwhiteincakebatterincreasedthebatterviscosityatambienttemperatureandminimumviscosityduringheating.Viscosityofthebatteratambienttemperaturewashigherwhenfresheggwhitewasused.Onsettemperaturewasnotaffectedbytheadditionofdriedorfresheggwhite.Theadditionofhydrocolloids (xanthan,guar,carboxymethylcel-lulose[CMC])increasedtheviscosityatambienttemperature.Whentheminimumviscositiesofheatedbatterswerecompared,xanthanwasable tomaintainhigherbatterviscositiesthanguarandCMCatthesameconcentrations.Higherviscosityduringheatingwouldgivethebattersgreatercapacitytoretainexpandingairandresistsettlingofstarchgranulesthatimprovecakevolumeandcrumbgrain.

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. ConClusIon

Rheologicaldataarerequiredinproductqualityevaluation,engineeringcalculations,andprocessdesign.Inrheologicalstudies,cakebattersmostlyshowednon-Newto-nianshearthinningbehavior,andacorrelationwasobservedbetweenrheologicalpropertiesofcakebatterandfinalcakequality.Therheologicalpropertiesofcakebattersaremainlyaffectedby the typeandconcentrationsof the ingredients, thelevelofairincorporation,andtemperature.Theviscosityofbattersatambienttem-peraturesincreasesasafunctionofpostmillingtime.Softwheatflouriscommonlychlorinatedfortheproductionofcakes.Chlorinatedflourhadhigherviscositythanuntreatedflour.Heat-treatedflourcanalsobeusedasanalternativetochlorinatedflourastheyshowsimilarrheologicalproperties.Theadditionoffatimprovesairincorporation and foam stability and causes a decrease in apparent viscosities ofcakebatters.Usingfatreplacers,emulsifiers,sugars,andgumsalsoaffectstherheo-logicalbehaviorofcakebatters.Airincorporationduringmixingreducestheappar-entviscosityofbatter.Viscoelasticpropertiesofmanuallydosedbattersaredifferentthanthoseofbatterspassedthroughanautomaticdosingunit.Generally,thebatterviscosity decreases at the beginning of heating and then starts to increase at thestarchgelatinizationtemperature.

referenCes

Baik,O.D.,M.Marcotte, andF.Castaigne.2000.Cakebaking in tunnel typemulti-zoneindustrial ovens. Part II. Evaluation of quality parameters. Food Research Interna-tional33:599–607.

Baixauli,R.,T.Sanz,A.Salvador,andS.M.Fiszman.2007.Influenceofthedosingprocessontherheologicalandmicrostructuralpropertiesofabakeryproduct.Food Hydrocol-loids21:230–236.

Bath,D.E.,K.Shelke,andR.C.Hoseney.1992.Fatreplacersinhigh-ratiolayercakes.Cereal Foods World37:495–500.

Boyd,J.,P.Sherman,andC.Parkinson.1972.FactorsaffectingemulsionstabilityandtheHLBconcept.Journal of Colloid Interface Science41:359–370.

Chang,C.N.,S.Dus,andJ.L.Kokini.1990.Measurementandinterpretationofbatterrheo-logicalproperties.InBatters and Breadings in Food Processing, Ed.K.KulpandR.Loewe,199–226.AmericanAssociationofCerealChemists,St.Paul,MN.

Cloke, J.D.,E.A.Davis,andJ.Gordon.1984.Relationshipofheat transferandwater-lossratestocrumb-structuredevelopmentasinfluencedbymonoglycerides.Cereal Chem-istry61:363–371.

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6 Cookie Dough Rheology

Meryem Esra Yener

Contents

6.1 Introduction................................................................................................. 1216.2 RheologicalMethods.................................................................................. 122

6.2.1 EmpiricalMeasurementMethods.................................................... 1226.2.1.1 DoughTestingEquipment.................................................. 1226.2.1.2 TextureProfileAnalysis..................................................... 1236.2.1.3 Compression....................................................................... 1236.2.1.4 Penetration.......................................................................... 123

6.2.2 FundamentalMeasurementMethods.............................................. 1236.2.2.1 ModifiedPenetrometer....................................................... 1236.2.2.2 TransientTests....................................................................1246.2.2.3 DynamicTests....................................................................1246.2.2.4 ExtensionalViscosity......................................................... 126

6.3 EffectsofIngredients.................................................................................. 1276.3.1 Water................................................................................................ 1276.3.2 SugarandSugarReplacers.............................................................. 1286.3.3 FatandFatReplacers....................................................................... 1326.3.4 ProteinContentinFlourandProteinModifiers.............................. 139

6.4 InterrelationshipbetweenRheologicalPropertiesofDoughandQualityofCookies...................................................................................... 145

6.5 Conclusion................................................................................................... 145References.............................................................................................................. 145

. IntroduCtIon

Cookiesandbiscuitsareproductsmadefromsoftflours.Lowcontentofprotein(8to10%inthegrain),lowwaterabsorption,andlowresistancetodeformationarethecharacteristicsthatdescribethesuitabilityofwheatforbiscuitproduction(Pedersenetal.,2004).Cookiesarecharacterizedbyaformulahighinsugarandfatandlowinwater.Cookiedoughiscohesivebuttoalargedegreelackstheextensibilityandelasticitycharacteristicsofbreaddough.Relativelyhighquantitiesoffatandsugarin dough provide dough plasticity and cohesiveness without the formation of theglutennetwork,andtheyproducelesselasticdough(Faridi,1990).Ahighlyelasticdoughisnotdesirableinbiscuitmakingbecauseitshrinksafterlamination.Inaddi-tion,andagaindependingontheformulation,cookiedoughtendstospread(becomelargerandwider)asitbakesratherthantoshrinkasdoescrackerdough.Spreadisanimportantqualityparameterforcookies.

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Determiningrheologicalpropertiesofdoughyieldsvaluableinformationcon-cerningthequalityoftherawmaterials,themachiningpropertiesofthedough,andpossiblythetexturalcharacteristicsofthefinishedproduct(Faridi,1990).Mixingtimeormixingprotocolhasanimportanteffectonrheologicalpropertiesofbiscuitdough(Maache-Rezzougetal.,1998a;ManoharandRao,1999a).Generally,alongmixingtimeresultsinthesofteningofdoughandreductionsinbothviscosityandrelaxationtime.However,theeffectofmixingtimecannotbedifferentiatedfromthecompositionofcookiedoughandwillbediscussedasintegratedtotheeffectsof ingredients.Themainingredients thataffect therheologyofcookiedougharewater,sugar,fat,andtheproteincontentoftheflour.Theeffectsoftheseingredientsonrheologicalpropertiesofcookiedoughandspreadofcookiesarediscussed inthischapter.Briefdescriptionsoftherheologicalmethodscommonlyusedforthispurposearealsogiven.

. rheologICalMethods

6.2.1 emPiriCalmeasuremenTmeThods

Empiricalinstrumentsarecommonlyusedtodeterminetheflowbehavioroffoodproducts.Becausetheydonotmeasurefundamentalrheologicalproperties,theyaremostlyindexers.However,theresultsareusedbothinqualitycontrolandincorrela-tiontosensorydata(Steffe,1996).

... doughtestingequipment

Cereal chemists are familiar with dough testing equipment and use it widely toinvestigatedoughbehavior.This equipment includes the farinograph,mixograph,extensograph,andalveograph.

The farinograph and mixograph are torque-measuring devices that provideempiricalinformationaboutmixingpropertiesofflourbyrecordingtheresistanceof dough to mixing. In the farinograph, there is a kneading type of mixing; themixographinvolvesaplanetaryrotationofverticalpins.The informationderivedfromfarinogram(consistencyversustimecurve)andmixogram(torqueversustimecurve)isgivenbySahinandSumnu(2006)indetail.Incookiedough,theheightofthefarinogrambandisusedasameasureofdoughconsistency,andbandwidthisusedasameasureofdoughcohesiveness(JacobandLeelavathi,2007;OlewnikandKulp,1984).Deducedparametersofthemixogramssuchasinstantaneousspecificenergyandtotalspecificenergywereusedtoanalyzerheologicalbehaviorofbiscuitdoughaswell(Maache-Rezzougetal.,1998a,1998b).Instantanenousspecificenergyisdefinedastheenergy(J/kg.s)transmittedtothebiscuitdoughduringthemixingcycle.Totalspecificenergyistheintegraloftheinstantaneousspecificenergydur-ing theentiremixingoperation.Softandstickydough is reported tohavehighertotalspecificenergythanfirmandinhomogeneousdough,becausesoftdoughsticksandwrapsitselfroundthemixerblades,increasingthetransmittedenergy.

Theextensographandalveographmeasurerheologicalpropertiesofdoughaftermixing.Theextensographmeasuresthedoughresistancetostretchingandextensi-bility;thealveographmeasuresthepressurerequiredtoblowabubbleinasheeted

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Cookie Dough Rheology

piece of dough. The typical extensogram and alveogram are given by Sahin andSumnu(2006).Extensibilityofcookiedough(inmm)wasobtainedbyextensographbyPedersenetal.(2004).AlveographP(maximumoverpressureneededtoblowadoughbubble) isanindexofresistancetodeformation,L (theaverageabscissaatbubblerupture)isanindexofdoughextensibility,W(thedeformationenergy)isanindexofdoughstrength,andtheP/L(curveconfigurationratio)isanindexoftheelastictoviscouscomponentofdough(i.e.,glutenbehavior)(Agyareetal.,2004).

... textureProfileanalysis

Intextureprofileanalysis(TPA),abitesizeoffood(usuallya1-cmcube)iscompressedtwotimesbetweentwoplates,usuallyto80%ofitsoriginalheight.Becausethistestisintendedtoreflectthehumanperceptionoftexture,thefirstandsecondcompressionsarereferredtoasthefirstandsecondbites.Atextureprofilecurve,whichisforceversustime,isanalyzedtogivetexturalproperties(SahinandSumnu,2006;Steffe,1996).Two-biteTPAwasperformedtomeasureconsistency,hardness,cohesiveness,adhesiveness,andstickinessofbiscuitdoughusingeithertheInstronUniversalTestingMachine(ManoharandRao,1997a,1997b,1999a,1999b,1999c)oratextureanalyzer(Zouliasetal.,2000).

... Compression

Acompressiontestmeasuresthedistancethatafoodiscompressedunderastan-dardcompressionforceortheforcerequiredtocompressafoodastandarddistance(SumnuandSahin,2006).TheInstronUniversalTestingMachinewasusedtomea-suretheforcerequiredtocompresscookiedough50%(Gaines,1990)or80%(JacobandLeelavathi,2007),andthisforcewasusedasameasureofconsistencyandhard-nessofthecookiedough,respectively.

... Penetration

Penetrometersaredesignedtomeasurethedistancethataconeoraneedlesinksintoafoodundertheforceofgravityforastandardtime(SumnuandSahin,2006).Atextureanalyzerwasusedtomeasuretheforcethata6-mm-diametercylinderprobepenetratestoadistanceof20mmincookiedough(Zouliasetal.,2000).

6.2.2 FundamenTalmeasuremenTmeThods

Fundamentalmeasurementmethodsincludemeasurementofstrain(ε)whenastress(σ)isappliedtoamaterial,orviceversa.Stressisdefinedastheforceappliedperunitarea;strainisdefinedastheamountofdeformationrelativetotheinitialdimensions(height,length,orvolume).Generally,therelationbetweenthetwoisexpressedasmodulus(σ/ε)orascompliance(ε/σ).Forviscoelasticmaterialslikedough,thefundamentaltestsareperformedunderunsteady-stateconditions,liketransientanddynamictests.

... ModifiedPenetrometer

Generally, the penetrometer is used to determine the consistency of fats on thebasisofdistancemovedbytheconeorneedlethroughthematerialinaparticular

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time(Steffe,1996).ThepenetrometerwasmodifiedbyManoharandRao(1992)toperformauniaxialcompressionbetweentwoplates.Theoptimumcompressionweightwasfoundtobe410gforbiscuitdough(2.2cmdiameter×1cmheight).Theinitialheight(h1)andtheheightofthedoughaftercompressionof10sec(h2)wererecorded.Thecompressionplatewasliftedup,thedoughwasallowedtorecoverfor1min,andtherecoveredheight(h3)wasmeasured.Thecomplianceandelasticrecoverywerecalculated(ManoharandRao,1992)as

Compliance (%)= −

×h h

h1 2

1100 (6.1)

Elastic recovery (mm)= −( )×h h3 2 10 (6.2)

ThereadershouldrealizethatEquation6.1isthedefinitionofstrainbutnotcompli-ance.However,definingcomplianceasinEquation6.1doesnotchangetheinterpre-tationofthephysicalmeaning.

... transienttests

Intransienttests,theresponseofamaterialasafunctionoftimeismeasuredaftersubjectingthematerialtoaninstantanenouschangeineitherstrainorstress.Creeprecoveryandstressrelaxationarethetwocommontransienttests.Increeprecovery,aconstantstressisappliedtoamaterial,anditsstrainisrecordedasafunctionoftime (creep).Then the stress is removed,and the strain is recordedasa functionoftime,calledrecovery.Incookiedough,themaximumstrainisameasureofitsextensibility,andpercentrecoveryisthemeasureofitselasticity.Instressrelaxation,aconstantstrainisappliedtoamaterial,andthestressrequiredtokeepthisstrainconstantisrecordedasafunctionoftime.Anelasticsolidneverrelaxes,andanidealliquidimmediatelyrelaxestozero.Thelargertherelaxationtime,themoreelasticisthematerial.Amechanicalanalogofanelasticsolidisspring,andthatofanidealliquidisdashpot.ThebehaviorofviscoelasticmaterialsisexpressedbymechanicalmodelssuchasMaxwell,Kelvin-Voight,andBurgermodels.ThereadercanobtainmoredetailedinformationaboutthesemodelsinSteffe(1996).

Maache-Rezzougetal.(1998a,1998b)performedastressrelaxationtestunderlubricateduniaxialcompressionandusedtheMaxwellmodeltodetermineviscosity(η)andrelaxationtime(λrel).Pedersenetal.(2004,2005)performedcreeprecoverymeasurementswithacreepandrecoverytimeof300sandastressvalueof10Patodeterminemaximumstrainandpercentrecoveryofcookiedough.

... dynamictests

Indynamictests,anoscillatorystrainisappliedtoamaterialandtheresultingstressismeasured.Whenviscoelasticmaterialsaredeformed,partoftheenergyisstored(asinanelasticsolid)andpartofitisdissipatedasheat(asinaliquid).Therefore,whenalinearviscoelasticmaterialissubjectedtoaperiodicallyvarying(frequency,

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ω)stress,thestrainwillalsovaryperiodicallybutoutofphasewithstress.Theresultisexpressedwithastressequation(Steffe,1996)as

σ ω= ′ + ′′( )G Gγ γ (6.3)

whereγisshearstrain, γ isshearrate,G′isthestoragemoduluswhichisthemeasureofelasticbehaviorofamaterial,andG″ isthelossmoduluswhichisthemeasureofliquidbehaviorofamaterial.Storagemodulus(G′)andlossmodulus(G″)arefunc-tionsofthephaselag(δ)betweenstressinput(σ0)andstrainoutput(γ0),asfollows:

′ =

( )G

σδ0

0γ

cos

(6.4)

′′ =

( )G

σ

γδ0

0

sin (6.5)

δis0°foranidealelasticsolidand90°foraNewtonianfluid.Tangentofthephaselagis(tanδ)alsoapopularmaterialfunctiontodescribeviscoelasticbehaviorandisdefinedas

tanδ =

′′′

GG (6.6)

Thedynamic testsshouldbeperformedwithin the linearviscoelastic regionofamaterialanddeterminedbyastresssweep.Frequencysweepwithinthelinearvis-coelasticregionisusedtodeterminetheeffectsofdifferentingredientsinacookiedoughformulation.Temperaturesweepexplainsthedoughbehaviorduringbaking.

Rheological properties of short doughs (standard, firm-fat, lowfat, liquid oil,sugar-free, and starch doughs) were determined by using a controlled stress rhe-ometeratsmalldeformation(Baltsaviasetal.,1997).Therheometerwasoperatedinastresssweepatafixedangularfrequencyof6.28rad/s(1Hz),intimesweepatafixedstrainamplitudeof2×10−4andanangularfrequencyof6.28rad/s,infre-quencysweepatafixedstrainamplitudeof2×10−4.Thelinearviscoelasticregionofshortdoughswerefoundtobeverylimited—nonlinearitystartedatastrainabout2×10−4exceptwithliquid-oildoughwherethisvaluewas4×10−4.

Agyareetal. (2004)determined theeffectof substitutingcanolaoil/caprylic-acid-structuredlipidforpartiallyhydrogenatedshorteningonrheologyofsoftwheatflourdoughbyperformingfrequencysweepfrom0.01to20Hzat25°Cusingastrainof0.02.LeeandInglett(2006)studiedtheeffectofreplacingshorteningincookiesby20%jet-cookedoatbran,whichisacarbohydrate-basedfatreplacer.Viscoelasticpropertiesofdoughweredeterminedbyusingacontrolledstrainrheometer,byper-formingoscillatorytestingoverafrequencyrangeof0.01to10Hzatastrainof5×10−3,whichwasinthelinearviscoelasticregionforallsamples.

Pedersenetal.(2004)studiedrheologicalpropertiesofsemisweetbiscuitdoughfromdifferentcultivarsand theeffectofchemicalandenzymaticmodificationon

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doughrheology(Pedersenetal.,2005)byusingacontrolledstressrheometer.Thelinearviscoelasticregionwasdeterminedtobeuptostrainof1.5×10−3byperform-ingastrainsweepatafrequencyof1Hz.Atargetstrainof1×10−3correspondingtoastressvalueof10Pawasusedinalltheexperiments.Afrequencysweepwasper-formedintherangefrom0.1to60Hz;scatteringofdatawasobservedabove30Hz.

... extensionalviscosity

Extensionalflowisanimportantaspectofdoughprocessingduringsheeting,anditdoesnotinvolveshearing.Althoughtherearethreebasictypesofextensionalflow—uniaxial,planar,andbiaxial (Steffe,1996)—biaxialextensionalviscosity iscom-monlymeasuredincookiedough(Baltsaviasetal.,1999a,1999b;LeeandInglett,2006;ManoharandRao,1997a,1997b,1999a,1999b,1999c).Biaxialextensionalflow is achieved in a lubricated squeezing flow between parallel plates (uniaxialcompression).Thesamplebetweentheplatesiscompressedwithaconstantvelocity(constantdeformationrate)ofthetopplate.Thisiscalledcrossheadspeed,andthetypicalvaluesusedforcookiedoughare6,18,and60mm/min(LeeandInglett,2006);50mm/min(ManoharandRao,1997a,1997b,1999a,1999b,1999c);and1,10,and100mm/min(Baltsaviasetal.,1999a,1999b).Whencompressingthesamplewithaconstantvelocity,theforceexertedonthesampleisrecordedasafunctionof

time F t( )( ) .Thestressexertedisdefinedas

σπ

=F t

R( )

2 (6.7)

whereRistheradiusofthesampleinthecaseofconstantarea(Steffe,1996)asusedbyBaltsaviasetal.(1999a,1999b),or

σ=

F tA t

( )( )

(6.8)

inthecaseofconstantvolume(Steffe,1996)asusedbyManoharandRao(1997a,1997b,1999a,1999b,1999c)andLeeandInglett(2006).Thebiaxialstrainrate, εB (1/s),isgiven(Steffe,1996)by

εB

vh t

vh vt

= =−2 2 0( ) ( )

(6.9)

where v isthecrossheadspeed(m/s)and h0 istheinitialheightofthesample.Theapparentbiaxialextensionalviscosity(Pa.s)isgivenby

η

σεB

B=

(6.10)

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The apparent biaxial extensional viscosity of cookie dough is expressed bythe power law model (Baltsavias et al., 1999a, 1999b; Lee and Inglett, 2006)atlargedeformation,as

η εB B

nK= − 1 (6.11)

whereKistheconsistencyindex,andn istheflowbehaviorindex.

. effeCtsofIngredIents

6.3.1 waTer

Water is an essential ingredient in dough formation, because it is necessary forsolubilizingotheringredientsforhydratingproteinsandcarbohydratesandforthedevelopmentofglutennetwork.Thedough,having12.5%fatcontaining13.3%to15.5%water,wasnot consistentbecause they lackedhydration.Thedoughswithhighwatercontent(>21%)wasextremelysoftandsticky,making it impossible towork.An increase inwatercontent led toasignificantdecrease indoughviscos-ity (η)andaslight reductionof the relaxation time(λrel), indicating reductionofelasticity (Table6.1). The biscuits expanded lengthwise, with a smaller thickness(Maache-Rezzoug,1998b).Similarly,increasingwatercontentofbiscuitdoughby3%increasedcomplianceanddecreasedextrusiontime,apparentbiaxialextensionalviscosity (ηB), and consistency, indicating a decrease in dough viscosity. Doughbecamemorecohesivebutsoft,adhesive,andsticky.Onthecontrary,anincreaseinelasticrecoveryindicatedincreasedelasticpropertiesofdough(ManoharandRao,1999b).

Theeffectofwatercontentondoughpropertieswasreportedtovarywiththequantitiesandrelativedistributionoffat(OlewnikandKulp,1984).Indepositdough,

taBle.

effectofWaterContentonviscosity(η)andrelaxationtime( λrel)of

BiscuitdoughWaterContent

(%)η ×0-

(Pa.s)λrel (s)

17.0 8.8 2.05

18.0 4.7 1.85

19.0 3.8 1.63

20.0 3.2 1.45

21.0 2.8 1.30

22.5 1.7 1.03

Source:AdaptedfromMaache-Rezzoug,Z.,Bovier,J.M.,Allaf,K.,andPatras,C.,Journal of Food Engineering,35,23,1998b.Withpermission.

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whichhas63%fat,water(9to13%)didnotaffecttheconsistencyandcohesivenessvery much, due to the dominating effect of fat. In wire-cut dough that has 45%fat,water(14to20%)increasedconsistency,becausetheadditionofwaterreducedthepercentageoffat,allowingthehydrationofflouranddevelopmentofaglutennetwork.Inrotary-moldeddoughthathas27%fat,thesmearingoffatoverthepar-ticlesofsugarandflourwasretardedduringmixingbecausethedoughwaslowfat.Theincompleteformationoffatfilmincreasedtheaccessibilityofsugarcrystalstowater,resultinginfaster,moreextensiveformationofsugarsyrup.Doughconsis-tencywasreducedasthequantityofwaterincreasedfrom13to16%.Moredoughliquiddecreaseddoughconsistencyandincreasedcookiespreadofsugar-snapcook-ies,aswell(Gaines,1990).

6.3.2 suGarandsuGarrePlaCers

Sugarisanimportantingredientofshortdoughbiscuits.Itcontributestotexture,fla-vor,sweetness,andcolorofbiscuits(ManoharandRao,1997).Theeffectofsugarondoughbehaviorisanimportantfactorinbiscuitmaking.Sugarcausessofteningofthedough,dueinparttocompetitionbetweentheaddedsugarandtheavailabilityofwaterinthesystem.Sugarrestrictsthedevelopmentofglutennetworkbycompetingforwaterthatotherwisewouldhavebeenabsorbedbygluten.Thelimitedamountofwaterusedinbiscuitformulation,andalsoitsnonavailabilitytoproteinandstarch,partiallycontributestothecrispnessofbiscuits.

In the farinograph,consistencyofwire-cutdough remained fairlyconstantat30%,45%,and60%addedsugar,butcohesivenessincreasedat the60%level.Indepositcookiedough,addedhighlevelsofsugarupto55%increasedconsistencyandcohesivenesssharply.However,inrotary-moldeddough,highlevelsofsucroseupto50%causedasharpreductionindoughconsistencyandcohesiveness.Thisisbecauseofextrawater(10%weightofdough)addedintothefarinographbecauselowfatandwaterlevelsinthiscookieformularesultedincrumblydoughsthatwereunsuitablefordirectfarinography(OlewnikandKulp,1984).

Mixogramsofbiscuitdoughshowedthatthedoughchangedfromasolidandcon-sistenttexturetoanextremelysofttextureassugarcontentincreasedfrom20to50%(Maache-Rezzougetal.,1998b).Theadditionofsugartotheformuladecreaseddoughviscosity(η).Atsugarcontentslessthanorequalto30%,relaxationtime(λrel)ofdoughwas constant; at sugar contents between 30 and 50%, relaxation time was reduced(Table6.2).

Theeffectsofmixingtime,sugar level,andtypeonrheologicalpropertiesofbiscuitdoughpreparedfromweakflour(8.8%gluten)weredeterminedbyManoharandRao(1997a,1997b).Prolongedmixingofdoughhaving300gsugar/kgofflourresultedinincreasedelasticproperties.Theoptimummixingtimewasselectedas180samong90,180,and300s(ManoharandRao,1997a).Increasingsugarcontentdecreased extrusion time, elastic recovery, apparent biaxial extensional viscosity,(ηB),consistencyandhardness,andincreasedcompliance,cohesiveness,adhesive-ness,andstickinessofbiscuitdough(Table6.3).Theseresultsindicatedthatincreas-ing thesugarconcentration resulted insoft (with lessviscosityandelasticity)butcohesivedoughthatwasadhesiveandsticky.Incorporationof20gofreducingsug-

52748.indb 128 2/6/08 2:26:07 PM



arsperkilogramofflour,insteadof300gsugarperkilogramofflour,likedextrose,liquidglucose(LG),invertsyrup(IS),andhigh-fructosecornsyrup(HFCS),affectedtherheologicalcharacteristicsinthesamewayasincreasingthesugarcontentintheformulation (Table6.4).However, thesyrupshadagreater influenceon the rheo-logicalcharacteristics(ManoharandRao,1997b).Spreadaswellasthicknessofthebiscuitsincreased,butdensitydecreasedsignificantlybytheadditionofsugar.

Zouliaset al. (2000) studied theeffectof sucrose replacementby fructoseorpolyolsondoughrheologyinlow-fatcookies.Polydextrosewasusedtoreplace35%offatinlow-fatcookies.Mannitoldoughwasveryfirmanddifficulttosheet;how-ever,itpresentedmoderatevaluesofhardnessandconsistencyandthelowestadhe-siveness.Maltitolandfructoseresultedindoughwithhighvaluesofhardnessandconsistencyandlowadhesivenessandcohesiveness,whilelactitol,sorbitol,andxyli-tolhadtheoppositeeffects.Thexylitoldoughpresentedsomeproblemsinsheetingfortheformationofcookiesduetoitshighadhesiveness.Therheologicalpropertiesofdoughspreparedbylactitolandsorbitolweresimilartothosepreparedbysucrose(Table6.5).Cookieswithfructoseorpolyolswerelesssweetthansucrose-contain-ingones,butsupplementationwithacesulfame-K,whichdidnotinterferewiththedough rheology, increased sweetness and improved perceived flavor and generalacceptance.Thepropertiesofcookiespreparedwithmaltitol,lactitol,andsorbitolwereacceptable.Mannitolrestrictedspreadofcookies.

Whenrheologicalbehaviorofstandardandsugar-freeshortdoughswascom-paredatsmalldeformation,sugar-freedoughhadhigherstoragemodulus(G′)andlowerphaseangle(tanδ)thanthestandarddough(Table6.6),indicatingthatsugar-free dough was more solid and elastic (Baltsavias et al., 1997). The frequencydependency of storage modulus (G′) and phase angle (tanδ) of the sugar-freedoughweresimilartothoseofthestandarddough.Theydecreasedwithincreas-ing frequency up to 3 rad/s and then remained constant. At large deformation,shortdoughsbehaved likestrain rate thinning liquids (Baltsaviasetal.,1999a).Whentheapparentbiaxialextensionalviscosityofthedoughs(ηB

*)expressedwiththepowerlaw(Equation6.11),theconsistencyindex(K)ofthesugar-freedough

taBle.

effectofsugarContentonviscosity(η)andrelaxationtime(λrel )ofBiscuitdough

sugarContent(%)

η×0-

(Pa.s)λrel (s)

20 5.1 1.52

30 4.8 1.51

35 3.9 1.38

40 3.5 1.14

50 3.0 1.03

Source: AdaptedfromMaache-Rezzoug,Z.,Bovier,J.M.,Allaf,K.,andPatras,C.,Journal of Food Engineering,35,23,1998b.Withpermission.

52748.indb 129 2/6/08 2:26:09 PM


0 Fo

od

Engin

eering A

spects o

f Bakin

g Sweet G

oo

ds

taBle.effectofsugarContentonrheologicalCharacteristicsofBiscuitdoughsugar(g/kg)

extrusiontime

(s)

Compliance(%)

elasticrecovery×0

(mm)

ηB×0−

(Pa.s)Consistency

(n.s)hardness

(n)Cohesiveness adhesiveness

(n.s)stickiness

(o)

250 70a 35.9a 5.51a 2.54a 866a 814a 0.138a 35.8c 44.8c

300 45b 40.6b 4.60b 1.91b 786b 662b 0.194b 54.3b 50.3b

350 23c 49.8a 3.80c 1.41c 616c 512c 0.223a 57.6a 69.5a

1 Valuesforaparticularcolumnfollowedbydifferentlettersdiffersignificantly(p<0.05). ηB:Apparentbiaxialextensionalviscosity,at50%compression.Source: AdaptedfromManohar,R.S.,andRao,P.H.,Journal of the Science of Food and Agriculture,75,383,1997b.Withpermission.

taBle.

effectofdifferenttypesofreducingsugarsonrheologicalCharacteristicsofBiscuitdough

sugartype extrusiontime(s)

Compliance(%)

elasticrecovery×0

(mm)

ηB×0−

(Pa.s)Consistency

(n.s)hardness


(n.s)stickiness

(o)

Control 45a 40.6c 4.60a 1.91a 786a 662a 0.194d 54.3c 50.3c

Dextrose 36b 44.2b 4.10b 1.64b 654b 586b 0.202cd 55.8bc 54.8b

LG 26c 48.8a 3.80d 1.42c 524c 492c 0.220ab 57.8b 70.5a

IS 24c 48.6a 3.95c 1.41c 538c 476c 0.210bc 62.5a 69.8a

HFCS 22c 49.8a 3.80d 1.36d 530c 474c 0.230a 64.3a 71.5a

1Valuesforaparticularcolumnfollowedbydifferentlettersdiffersignificantly(p<0.05).

2Controlis300gsugar/kgofflour;reducingsugarsareat20g/kgofflourlevel;LG,liquidglucose;IS,invertsugar;HFCS,high-fructosecornsyrup.

3ηB:Apparentbiaxialextensionalviscosity,at50%compression.

Source: AdaptedfromManohar,R.S.,andRao,P.H.,Journal of the Science of Food and Agriculture,75,383,1997b.Withpermission.

52748.indb 1302/6/08 2:26:10 P

M



washigher,butitsflowbehaviorindex(n)waslowerthanthoseofstandardandsucrosesyrupdoughs(Table6.7).TheeffectsofsucrosecontentandmixingtimeontherheologicalpropertiesofshortdoughswerefurtherstudiedbyBaltsaviasetal.(1999b)atlargedeformation.Doughswithdifferentsugarlevelswerepreparedbydissolvingsucrose inwaterbeforeadding to thedough.Thedoughsdenotedas sucrose syrup 1, 2, and 3 corresponded to 64.6, 50, and 40% sucrose solu-tions,respectively.Thedoughscalledsugar-free1,2,and3containednosucrose,but thecompositionsof theother ingredientswerethesamein theformulations(Table6.8andTable6.9).Regardlessof thedough type,mixing timedecreased

taBle.

effectofsweetenersonrheologicalPropertiesoflow-fatCookiedoughsweetener Fpenetration

(n)FtPa

(n)Consistency

(n·s)adhesiveness

(n·s)Cohesiveness

Sucrose 2.4a 66.8ab 69.6ab 6.79c 0.656b

Fructose 3.0a 69.9b 78.3b 4.42b 0.548a

Maltitol 3.2a 69.3b 74.5b 4.83b 0.534a

Lactitol 2.9a 58.2ab 60.2ab 6.40c 0.693b

Sorbitol 2.9a 51.3ab 51.0ab 6.06c 0.665b

Xylitol 2.4a 46.2a 47.5a 7.38c 0.638b

Mannitol 9.7b 59.0ab 55.9ab 1.55a 0.643b

1Valuesforaparticularcolumnfollowedbydifferentlettersdiffersignificantly(p<0.05).

Source:Zoulias,E.I.,Piknis,S.,andOreopoulou,V.,Journal of the Science of Food and Agriculture,80,2049,2000.Withpermission.

taBle.

dynamicrheologicalPropertiesofshortdoughsatsmalldeformation

g‘×0−

(n/m)tanδ

Standarddough 6.69 0.255

Firm-fatdough 8.73 0.277

Low-fatdough 4.34 0.390

Liquid-oildough 0.22 0.525

Sugar-freedough 7.50 0.238

Starchdough 5.36 0.202

1 Resultsweretaken1haftertheendofmixing,T=20°C, ω = 6.28rad/s, γmax =2×10−4.

Source: Baltsavias,A.,Jurgens,A.,andvanVliet,T.,Journal of Cereal Chemistry,26,289,1997.Withpermission.

52748.indb 131 2/6/08 2:26:11 PM



thedoughconsistencysignificantly(Table6.8).Inaddition,itdrasticallychangedtheshapeofthestress–straincurveforsugar-freedough(Figure6.1).Thestress–straincurvesforthesugar-freedoughsindicatedastrongerelasticcontributiontothedeformation thandid thoseforsucrosesyrupdoughs.Sucrosesyrupdoughsexhibitedprominentyieldingandflowbehavior.Theirapparentbiaxialextensional

viscosity(ηB)decreasedwithincreasingsucrosecontent(Table6.9).

6.3.3 FaTandFaTrePlaCers

Fatformsoneofthebasiccomponentsofacookieformulationandispresentatrelativelyhigh levels.Fat acts as a lubricant andcontributes to theplasticityofthecookiedough.Itpreventsexcessivedevelopmentoftheglutennetworkduring

taBle.

ConsistencyIndex(K)andflowBehaviorIndex(n)forapparentBiaxialextensionalviscosity(ηB)ofshortdoughs

K(Pasn) nStandarddough 1.1 0.10

Firm-fatdough 2.9 0.15

Low-fatdough 12.1 0.31

Sucrosesyrupdough 1.2 0.12

Sugar-freedough 1.4 0.03

Starchdough 0.8 0.09

1 ValueswerecalculatedatεB=0.2

Source: Baltsavias,A.,Jurgens,A.,andvanVliet,T.,Journal of Cereal Science, 29,33,1999a.Withpermission.

taBle.

effectofMixingonConsistencyIndex(K)andflowBehaviorIndex(n)forapparentBiaxialextensionalviscosity(ηB)ofsucrosesyrupandsugar-freedoughs

Mixingtime(min) K×0−(Pasn) n

Sucrosesyrup1(64.6%)

2 1.8 0.12

8 1.3 0.14

20 0.7 0.09

Sugar-free1

2 4.7 0.08

8 1.6 0.04

20 1.0 0.02

1Variousdoughsmixedfor8min;valueswerecalculatedatεB=0.2

Source: Baltsavias,A.,Jurgens,A.,andvanVliet,T.,Journal of Cereal Science, 29,43,1999b.Withpermission.

52748.indb 132 2/6/08 2:26:11 PM



mixing.Thepresenceof fatcontributes to the reductionof theelasticnatureofdoughandthereforetheshrinkingofthedoughduringmolding.Althoughintech-nological respects (consistency of dough), fat has similar effects to sugar, theirphysicochemicalrolesaredifferent.Theglobulesoffatsurroundtheproteinsandstarch,isolatethem,andpreventtheformationofpolymers,therebyreducingthedensityofthenetwork(Maache-Rezzougetal.,1998b).

Mixographresultsshowedthatan increase in thefatcontentofbiscuitdoughfrom 5 to 25% decreased the mixing energy. Dough was more homogenous andsoftwhenthefatcontentincreasedfrom15to20%.Theadditionoffatsoftenedthedoughanddecreasedviscosity(η)andrelaxationtime(λrel)(Table6.10).Fatcontrib-utedtoanincreaseinlengthandtoareductioninthicknessandweightofthebiscuits

taBle.

ConsistencyIndex(K)andflowBehaviorIndex(n)forapparentBiaxialextensionalviscosity(ηB

* )ofshortdoughsK×0−(Pasn) n

Sucrosesyrup1(64.6%) 1.3 0.14

Sucrosesyrup2(50%) 1.2 0.08

Sucrosesyrup3(40%) 1.4 0.08

Sugar-free1 1.6 0.04



1Mixingtime=8min;ValueswerecalculatedatεB=0.2

Source: Baltsavias,A.,Jurgens,A.,andvanVliet,T.,Journal of Cereal Science, 29,43,1999b.Withpermission.

0 0.2 0.4 0.6 0.8 1.0εb (–)

10

20

30

40

σ (k

N/m

2 )

fIgure. Stress–straincurvesforvariouscookiedoughformulations:sucrose-syrup1(opensymbols),sugar-free1(closedsymbols);mixingtime=2min(triangles);mixingtime=8min(diamonds);mixingtime=20min(circles).Initial εb =2.8×10−41/s.(FromBaltsavias,A.,A.Jurgens,andT.vanVliet,Journal of Cereal Science,29,43,1999b.Withpermission.)

52748.indb 133 2/6/08 2:26:13 PM



(Maache-Rezzougetal.,1998b).Increasingtheleveloffatfrom150g/kgflourto250g/kgflourincreasedcompliance,cohesiveness,andadhesivenessanddecreasedextrusiontime,elasticrecovery,apparentbiaxialextensionalviscosity(ηB),consis-tency,hardness,andstickiness(ManoharandRao,1999c).Therefore,increasingfatcontentproducedsoft,lessviscous,andlesselasticdough.

Astheamountoffatincreasedinwire-cutdoughsfrom40to50%,consistencyofthedoughvariedwithinafairlynarrowrange;however,cohesivenesswasconsid-erablyreduced.Depositdoughshadagreaterreductioninconsistencywithincreasedfatcontentfrom58to68%,aswellascohesiveness.Rotary-moldeddoughshaving27to29%fathadthehighestconsistencyandcohesivenessthantheothertwobutfollowedthesamepatternasthefatcontentincreased(OlewnikandKulp,1984).

Theeffectoffattypeoncookiedoughrheologywasstudiedbypreparingsugar-snapcookieswith fourdifferent fat types: emulsifiedbakery fat, emulsifiedmar-garine, nonemulsified hydrogenated fat, and sunflower oil (Jacob and Leelavathi,2007).Themoisture,protein, andglutencontentsof theflourwere11.9,9.7, and7.3%,respectively.Atthebeginningofmixing,themostconsistentdoughwasthatcontainingbakeryfat;theleastconsistentdoughwastheonecontainingsunfloweroil.However,consistencyofthedoughcontainingsunfloweroilincreasedwhiletheconsistencyof thedoughscontainingmargarineandbakery fatdecreasedduringmixing.Theconsistencyofthedoughcontaininghydrogenatedfatremainedalmostconstant.Attheendofmixing,thedoughcontainingsunfloweroilhadthehighestconsistency. The consistency of the dough containing hydrogenated fat remainedalmostconstant (Table6.11).The increase inconsistencyof thedoughcontainingsunfloweroilwasexplainedbyitslackingabilitytosmearalltheflourparticleslead-ingfordevelopmentofglutennetworkduringmixing.Thedecreaseinconsistencyofthedoughcontainingbothmargarineandbakeryfatwasduetothewellaerationofthedoughduringmixing.Althoughthedoughcontainingsunfloweroilwastheleast

taBle.0

effectoffatContentonviscosity(η)andrelaxationtime(λrel)ofBiscuitdough

fatContent(%)η ×0−

(Pa.s)λrel(s)

5 8.7 1.58

10 5.7 1.60

12.5 5.3 1.50

15 4.0 1.20

20 2.5 1.10

25 2.1 1.07

Source: Adapted fromMaache-Rezzoug,Z.,Bovier, J.M.,Allaf,K., andPatras,C.Journal of Food Engineering,35,23,1998b.Withpermission.

52748.indb 134 2/6/08 2:26:14 PM



cohesiveatthebeginning,itscohesivenessincreasedandremainedconstantduringmixing.Theleastcohesivedoughwasthatcontainingmargarineaftermixing.Whenthehardnesswasconsidered,thedoughcontaininghydrogenatedfatwasthehigh-est(Table6.11).ManoharandRao(1999c)reportedthatcookiedoughpreparedbyhydrogenatedfatwasthehardestamongthedoughspreparedbyotherfattypes,aswell.Cookiesmadebyemulsifiedbakeryfatandemulsifiedmargarinethatshowedconsistencydecreaseduringmixinghad the smaller spread ratio than theothers.Theadditionofemulsifierswithalevelof5g/kgflourtobiscuitdoughwasreportedtodecrease elastic recovery, indicating their contribution to the shortening effecton gluten (Manohar and Rao, 1999c). Furthermore, emulsifiers decreased extru-sion time, consistency, and apparent biaxial extensional viscosity (ηB), indicatingdecreaseindoughviscosity.Thedoughsbecamemorecohesivebutsoftwithloweradhesivenessandstickiness.

The rheological properties of short doughs prepared with different fat types,firm-fat,low-fat,andliquidoil,weredeterminedbothatsmalldeformation(Baltsav-iasetal.,1997)andatlargedeformation(Baltsaviasetal.,1999a).Atsmalldeforma-tion,lossmodulus(G″)tendedtobelinearoverawiderrangeofstraincomparedwithstoragemodulus(G′).Regardlessofcomposition,phaseangle(tanδ)increasedwithincreasingstrain,indicatingamoreliquid-likebehavior.Thestoragemodulus(G′)andlossmodulus(G″)curvesofthestandarddoughcrossedoveratastrainrateof10−1,showingthatthematerialchangedfromsolid-liketomoreliquid-like.Thechangesinducedbyshearwerereportedtobelesssevereinthecaseofthelow-fatandtheliquid-oildough.Butbothhadasignificantlylowerstoragemodulus(G′)andhigherphaseangle(tanδ)thanthestandarddough,indicatingthattheyweremoreliquid-likeandmoreeasilydeformed(Table6.6).Thefirm-fatdoughwasrelativelymoreliquid-likethanthestandarddough,withthephaseangle(tanδ)beingslightlyhigher.Butonthecontrary,higherstoragemodulus(G′)wasexplainedbyhigherairvolumefractioninthestandarddough.Reducingthefatcontentorreplacingsolidfatwithliquidoilbroughtaboutsubstantialchangesintheresultingdough.Theelasticcomponentbecamemorefrequencydependent,andthephaseangle(tanδ)increased

taBle.

effectoffattypeonrheologicalPropertiesofsugar-snapCookiedough

fattypefarinographdoughConsistency(Bu)

farinographdoughCohesiveness(Bu)

Compressionforce(hardness)

(kg)

0min 0min 0min 0min

Bakeryfat 440 360 60 80 3.0

Margarine 380 270 60 60 2.1

Hyodrogenatedfat 310 300 80 80 4.5

Sunfloweroil 200 400 20 120 2.9

Source: AdaptedfromJacob,J.andLeelavathi,K.,Journal of Food Engineering,79,299,2007.Withpermission.

52748.indb 135 2/6/08 2:26:15 PM



withincreasingangularfrequencyabove3rad/s.Thisbehaviorwasexplainedbytheformationofmorefat-disperseddoughbyloweringthefatcontentorreplacingsolidfatwithliquidoil.Atlargedeformation,alldoughsbehavedmorelikestrain-ratethinningliquids(Table6.7).Thedoughsshowedlargedifferencesinapparentbiax-

ialextensionalviscosity(ηB)dependingonfattype.Low-fatdoughhadthehighestconsistencyindex(K)andflowbehaviorindex(n).

Agyareetal.(2004,2005)studiedtheeffectofsubstitutingcanolaoil/caprylicacidstructuredlipid(SL)forpartiallyhydrogenatedshortening(at0,25,50,75,and100%)ontherheologyofsoftwheatflourdough(28.4%totallipidonflourbasis,43%moisturecontent).Figure6.2showsthattheadditionofpartiallyhydrogenatedshortening to untreated dough resulted in a significant decrease in resistance todeformation(AlveographP),doughextensibility(AlveographL),anddoughstrength(AlveographW).Thiswasattributedtothelubricationactionoftheaddedshorten-ing.SLsubstitution for shorteningdidnot significantlyaffectdoughdeformation

P (mm)

L (mm)

W (X 10^–4 J)P/L (X 10^–2)

Variation 0 Variation 1 Variation 2 Variation 3 Variation 4 Variation 5

Treatment

Alv

eogr

aph

Char

acte

ristic

0

20

40

60

80

100

120

140

160

180

fIgure. Effect of substituting varying levels of structured lipid (SL) for partiallyhydrogenatedshorteninginsoftwheatflourdoughonAlveographcharacteristics:Variation0:formulationwithoutshortening;Variation1:formulationwith100%shortening,0%SL;Variation2:formulationwith75%shortening,25%SL;Variation3:formulationwith50%shortening,50%SL;Variation4: formulationwith25%shortening,75%SL;Variation5:formulationwith0%shortening,100%SL.(FromAgyare,K.K.,Addo,K.,Xiong,Y.L.,andAkoh,C.C.Journal of Cereal Science,42,309,2005.Withpermission.)

52748.indb 136 2/6/08 2:26:20 PM



(AlveographP)anddoughstrength(AlveographW).However,doughextensibility(AlveographL)wasgreaterforformulationswith50%and75%SL.Inaddition,theratioofelastictoviscouscomponent(AlveographP/L)waslowerinformulationwith50%SLcomparedtothestandardshortening.Thisindicatedthatdoughwithformu-lations50%and75%SLhadgreaterextensibilityandlowelasticitythantheothers.This was also proved with large diameters (high spread) with the cookies bakedfromformulationswith50%and75%SL(Agyareetal.,2005).Indynamictesting,frequencysweepshowedthatallthedoughformulations,regardlessofthecontentofSL,gavehighervaluesofstoragemodulus(G′)andlossmodulus(G″)athigherfre-quencies,indicatingthattherecoveryofstresseddoughwasaslowprocess—thatis,thenetworkwasnotcompletelyelastic.Theadditionofshorteningtodoughloweredstoragemodulus(G′)andlossmodulus(G″)over theentirefrequencyrange,andincreasedSLsubstitutionfurtherdecreasedstoragemodulus(G′)andlossmodulus(G″),indicatingthatthedoughwasbeinglessviscousandlesselastic.ThiswastheresultofshorteningbeingsolidfatandSLbeingliquidatroomtemperature.

Leeand Inglett (2006)studied theeffectof replacingshortening (10,20,and30%)incookieswith20%jet-cookedoatbran,alsocalledNutrimOB(NU),whichisacarbohydrate-basedfatreplacer.Foralldoughs,storagemodulus(G′)andlossmodulus(G″)increasedwithfrequency(Figure6.3).Alldoughshadhighervaluesofstoragemodulus(G′)thanthoseoflossmodulus(G″),suggestingthattheyhadmoreelasticpropertiesthanviscousproperties.Thecontrolhadthehigheststoragemodulus(G′).IncreasingreplacementofshorteningwithNUfrom10to30%causedadecreaseinbothstoragemodulus(G′)andinlossmodulus(G″).ThisdecreaseinthedynamicviscoelasticpropertiesofcookiedoughscontainingNUwasattributedtotheirincreasedmoisturecontent.Thesamebehaviorwasobservedinextensional

Frequency (Hz)0.01 1000.1 1 10

CON 10NU 20NU 30NU

1.0E+06

1.0E+05

1.0E+04

1.0E+03

1.0E+00

1.0E–01

1.0E–02

tan δ

tan δ

G´,

G˝ (

Pa) G´

G˝

fIgure. EffectofNutrimOB(NU)onthedynamicviscoelasticpropertiesofcookiedough.(FromLee,S.andInglett,G.E.,International Journal of Food Science and Technol-ogy,41,553,2006.Withpermission.)

52748.indb 137 2/6/08 2:26:21 PM



viscosity.Atallstrainratestested,thebiaxialextensionalviscosity(ηB)decreasedasshorteningwasreplacedwithmoreNU.Atlargedeformation,thedoughsbehavedasshear thinningliquids.Consistencyindex(K)decreased,but theflowbehaviorindex (n) was not significantly decreased with shortening replacement with NU(Table6.12).However,duringbaking,afterstarchgelatinizationaround80to90°C,storagemodulus(G′)increasedwithtemperature.At120°C,whilethecontrolhadtheloweststoragemodulus(G′),increasingNUreplacementfrom10to30%gaverise to the increase instoragemodulus (G′), indicating that thedoughcontainingNUwasmoreelasticthanthecontrol,whichresultedinadecreaseindiameterofthecookiesmadebyNUcomparedtothecontrol(Figure6.4).Thisreversedelastic

Temperature (ºC)0 50 100 150 200

1,000,000

100,000

10,000

G´ (

Pa)

1,000

100

CON 10NU 20NU 30NU

fIgure. Changesinthestoragemodulusofcookieswithshortening(CON)anddiffer-entlevelsofNutrimOB(NU).(FromLee,S.andInglett,G.E.,International Journal of Food Science and Technology,41,553,2006.Withpermission.)

taBle.

ConsistencyIndex(K)andflowBehaviorIndex(n)forapparentBiaxialextensionalviscosity(ηB)ofCookiedoughsContainingshortening(Con)anddifferentlevelsofnutrimoB(nu)

K(Pasn) nCON 3.77a 0.19a

10NU2 3.67ab 0.20a

20NU3 3.34bc 0.20a

30NU4 3.11c 0.21a

1Valueswiththesamesuperscriptinthesamecolumnarenotsignificantlydifferentatthe5%level;210%NutrimOB;320%NutrimOB;430%=NutrimOB

Source:Lee,S.andInglett,G.E.,International Journal of Food Science and Technology,41,553,2006.Withpermission.

52748.indb 138 2/6/08 2:26:22 PM



behaviorduringbakingwasnotseeninthecookiesmadebyreplacingshorteningwithSL(Agyareetal.,2004).

6.3.4 ProTeinConTenTinFlourandProTeinmodiFiers

Generally,glutenisresponsiblefortherheologicalpropertiesofdough.Theeffectofproteincontentwasstudiedbyusingflourcontaining11.2%protein(0%addedgluten)to21.9%protein(15%addedgluten)(Maache-Rezzougetal.,1998a).Chang-ingtheproteincontentoftheflourfrom14to20%increasedthedoughviscosity(η)becauseitfavoredthestructuringoftheglutennetworkduringmixing.Upto14%andbeyond20%,theproteincontentappearedtohavenoeffectonrelaxationtime(λrel),whereasitincreasedlinearlybetween14and20%,indicatingthatwithinthisrangeproteincontentincreaseddoughelasticity(Table6.13).Consequently,proteincontentproducedanoverallreductioninthespreadofbiscuits.

Pedersenet al. (2004) studied the rheologicalpropertiesof semisweetbiscuitdoughsfromdifferentcultivars.Amongtheusedcultivars(Table6.14),Galateahasnohigh-molecular-weight(HMW)glutenins,andhenceitproducesdoughwithalmostnoglutenstructure.AlthoughRitmoisahardendospermcultivarclassifiedasbreadwheat,itisfrequentlyusedasbiscuitwheat.Forallcultivars,adecreaseinmaxi-mumstrainandincreaseinpercentrecoverywereobservedwithincreasingagingtime(Figure6.5).GalateahadthehighestextensibilityduetoitslowHMW-glutenincontentwhichresultsinahigherproportionofgliadins.Itiswellestablishedthatgliadinscontributetotheextensibilityandviscouspropertiesofwheatflourdough.ExtensibilityofRitmo,thehardendospermcultivar,wassignificantlylessthantheextensibilityofGalatea.However,itshowedthehighestpercentrecovery,beingmoreelasticduetotheelasticityinitsglutennetwork.ThecultivarsGalateaandEncore,

taBle.

effectofProteinContentonviscosity(η)andrelaxationtime( λrel )ofBiscuitdough

ProteinContent(%) addedgluten(%)η ×0−

(Pa.s) λrel (s)

11.2 0 3.3 1.10

12.8 2 3.5 1.15

14.4 4 3.8 1.11

15.8 6 7.1 1.22

17.3 8 7.6 1.40

18.7 10 9.0 1.60

20.0 12 9.4 1.70

21.2 14 9.4 1.72

21.9 15 9.4 1.70

Source:Adapted fromMaache-Rezzoug,Z.,Bovier, J.M.,Allaf,K.,andPatras,C.Journal of Food Engineering,35,23,1998b.Withpermission.

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taBle.

CreepandrecoveryCharacteristicsofsemisweetBiscuitdoughfromdifferentCultivarsCultivar Protein

inflour(%drymatter)

gluten(%offlour)

sed(ml) Wa(%offlour)

e(mm) r(Bu) Maximumstrain(%)

recovery(%)

Encore 9.0±0.7 17.7±0.3 21±5 54.8±2.0 117±11 187±59 1.19b 35.7c

Ritmo 9.1±0.9 21.2±2.7 32±6 56.8±3.0 128±16 232±108 0.87c 48.5a

Galatea 9.2±0.5 20.5±1.5 <10 53.7±3.5 — — 1.48a 35.7c

Claire 9.2±0.4 21.2±2.7 19±2 51.5±2.7 135±10 262±68 0.77c 40.3bc

Banker 9.4±0.6 21.6±4.3 21±3 53.7±3.3 128±4 177±49 1.26b 38.3bc

1SED,sedimentationvalue.2WA,waterabsorption(measuredbyFarinograph).3E,extensibilityafter45mindoughresting(measuredbyExtensograph).4R,resistanceafter45mindoughresting(measuredbyFarinograph).5Valuesforparticularcolumnfollowedbydifferentlettersdiffersignificantly(p<0.001);allyears1998,1999,2000.

Source: AdaptedfromPedersen,L.,Kaack,K.,Bergsøe,M.N.,andAdler-Nissen,J.,Journal of Cereal Science,39,37,2004.Withpermission.

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withveryweakglutenstructure,recoveredlessthantheothersdid.Clairewaslessextensiblethantheothersoftendospermcultivarsandrecoveredtoahighdegree.Resultsoffrequencysweeptestsfortwodistinctivecultivars,RitmoandGalatea,areshowninFigure6.6.Increasingfrequencyincreasedbothstoragemodulus(G′)andlossmodulus(G″).Correlationbetweenfrequencyandphaseangle(δ)dependedonthefrequencyrange.Thephaseangle(δ)decreasedatfrequencieslessthan0.5Hz,wasnearlyconstantbetween0.5and1Hz,andincreasedatfrequencieshigherthan1Hz.Thesedifferencesimplythatthedoughactedmorelikeasolidwhenimposedtoslowchangesinstresses,butveryfastchangeswouldmakethedoughactasaliquid.Measurementsofstoragemodulus(G′)wereunabletodistinguishbetweendoughs,whichhavedifferentstrengthofglutennetwork.However,phaseangle(δ)distinguishedbetweenthecultivarsthatweredifferentinthegliadin–gluteninratio.

When flourwas replacedby starch in a short dough formulation, the storagemodulus(G′)ofthedoughdecreased(Table6.6)becauseoftheabsenceofgluten.(Baltsavias et al., 1997). However, the frequency dependency of storagemodulus(G′)wassimilartothatofthestandarddough.

Pedersen et al. (2005) examined the effect of adding sodium metabisulfite(SMS),whichisadisulfitecleavingagent,andproteasetosemisweetcookiedough

0 100 200 300 400 500 600 700

1.601.401.201.000.800.600.400.200.00

Stra

in [%

]

Time [sec]

Ritmo

0 100 200 300 400 500 600 700

1.601.401.201.000.800.600.400.200.00

Time [sec]

Galatea

Stra

in [%

]

fIgure. Creeprecoverycurvesofbiscuitdoughfromtwocultivarswithdifferentrest-ingtimes:()10min,()25min,()35min(FromPedersen,L.,Kaack,K.,Bergsøe,M.N.,andAdler-Nissen,J.Journal of Cereal Science,39,37,2004.Withpermission.)

52748.indb 141 2/6/08 2:26:26 PM



preparedwiththesamecultivarsinlong-timebehavior(creeprecovery),aswellasintheshort-timebehavior(dynamictesting).Themainresultsofcreeprecov-eryandoscillationfromcultivars1998and1999areshowninTable6.15.Therewasasignificant(p<0.001)differencebetweenthetwoyearsforall therheo-logicalcharacteristicswithexceptionoflossmodulus(G″)andpercentrecoveryduetothehigherproteincontent(10.2%averageprotein,25.1%averagegluten)of wheat from 1999 compared with the one from 1998 (8.9% average protein,10.2%averagegluten).TheadditionofSMSorproteasehadasignificanteffectontherheologicalcharacteristics,withtheexceptionofpercentrecoveryin1998.Maximumstrain(i.e.,extensibilityofthedoughs)highlyincreasedbecauseSMSandprotease reduced thedisulfitebonds.Consequently, elasticitydecreasedasindicatedwiththedecreaseinpercentrecoveryof1999cultivars.Similarly,stor-agemodulus(G′)andlossmodulus(G″)decreasedwhereasphaseangle(tanδ)increased,indicatinglesselasticandliquid-likebehavior.TherewasasignificantinteractionbetweenthecultivarsandadditionofSMSandprotease.ThelargesteffectoftheadditionofmodifierswasobservedforthehardendospermRitmo.CultivarswithahighratioofgluteninsaresupposedtobeaffectedbySMSorproteaseadditionmore thancultivarswitha lowerratio.ThisagreedwellwiththelowcontentofgliadinsmeasuredforRitmo.MaximumreductioninthelengthofthebiscuitswasobservedforRitmo,whereasGalateawasslightlyreducedinlength.

Gaines(1990)studiedtheeffectofmodifyingagentsontheconsistencyofsugar-snap cookies made from different cultivars. Potassium iodate (the sulf-

G´ RitmoG˝ RitmoG´ GalateaG˝ Galatea

RitmoGalatea

0.1 1.0 10.0 100.0

100,000

10,000

1,000

100

40353025201510

0.1 1.0 10.0 100.0

Frequency [Hz]

Frequency [Hz]

Mod

ulus

[Pa]

δ [°]

fIgure. Frequencydependenceofdynamicviscoelasticpropertiesofbiscuitdoughsfromtwodifferentcultivars.(FromPedersen,L.,Kaack,K.,Bergsøe,M.N.,andAdler-Nis-sen,J.Journal of Cereal Science,39,37,2004.Withpermission.)

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hydryloxidizingagentthatincreasesglutenelasticity),L-cystein(thedisulfatecleavingagentthatdecreasesglutenelasticity),N-ethylmaleimide(whichblockssulfhydryl groups—initially increasing gluten elasticity), and dithioerythritol(thedisulfidecleavingagentthatbondswiththeresultingdisulfidebonds,remov-ing them from further thiol interchange) were studied. L-cystein did not sig-nificantlychangetheconsistencyofthedoughsmadefromanycultivars.Therewasnospecificpatternofresponseofdoughconsistencyorcookiediametertothemodifiers.Dithioerythritolhadthemosteffectonthedoughconsistency.Itreducedtheconsistencyandspreadofcookiesmadefrommostofthecultivars.

Theeffectsofprotein-modifyingagentson the rheologicalcharacteristicsofbiscuitdoughswerestudiedbyMonaharandRao(1997a).Incorporatingoxi-dizing agents potassium bromate (PB) and ascorbic acid (AA) or the sulfhy-dryl blocking agent N-ethylmaleimide (NEMI), produced significant changeinanyoftherheologicalcharacteristicsstudied(Table6.16).Thissuggeststhattheconditionsinthebiscuitdoughwerenotfavorabletooxidizingagents,andtherewaslittleinvolvementofinterchangereactionsofsulfhydrylanddisulfitegroupsinthistypeofbiscuitdough.However,L-cysteinhydrochloride(LCS)and dithioerythritol (DTE), two disulfite cleaving agents, reduced the extru-sion time, apparent biaxial extensional viscosity, consistency, and hardnessand increased thecompliance,adhesiveness, andcohesiveness.The reductionofelasticrecoveryinthepresenceofthedisulfidecleavingagentsindicatedaweakeningoftheglutennetwork.

taBle.rheologicalPropertiesofsemisweetBiscuitdoughwithadditionofsodiumMetabisulfite(sMs)andProtease,MeansofCultivarsand

noaddition additionofsMs(0mg/kg)

additionofProtease(00mg/kg)

Maximumstrain(%)

1998 1.23a 2.46b 2.00b

1999 1.19a 4.36c 3.16b

Recovery(%) 1998 36.80a 33.88a 35.66a

1999 41.07a 33.21b 35.82b

G′ (kPa) 1998 17.20a 10.68c 13.36b

1999 16.79a 8.48b 10.04b

G″ (kPa) 1998 7.28a 5.02c 6.03b

1999 7.79a 4.54b 5.07b

tanδ 1998 0.42a 0.46b 0.45b

1999 0.46a 0.52b 0.50b

logG″/logfrequency

1998 0.19a 0.22c 0.21b

1999 0.22a 0.28c 0.26b

1Meanswithinarowfollowedbydifferentlettersaresignificantlydifferent(p≤0.05).Source:Pedersen,L.,Kaack,K.,Bergsøe,M.N.,andAdler-Nissen,J.Journal of Food Science,70,152,

2005.Withpermission.

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taBle.effectofProteinModifyingagentsontherheologicalCharacteristicsofBiscuitdough

Modifyingagent

extrusiontime(s)

Compliance(%)

elasticrecovery×0

(mm)

ηB×0−

(Pa.s)Consistency

(n.s)hardness


(n.s)stickiness

(o)

Control 45a 40.6b 4.60a 1.91a 786a 662a 0.194b 54.3b 50.3b

PB 44a 40.2b 4.55a 1.92a 792a 656a 0.198b 52.2bc 52.3b

AA 45a 40.1b 4.65a 1.89a 764b 652a 0.192b 51.6c 51.6b

LCS 35b 43.2a 3.60b 1.62b 718c 598b 0.232a 58.6a 54.6c

NMI 45a 40.4b 4.50a 1.92a 772ab 660a 0.196b 54.6b 50.4b

DTE 38b 43.3a 3.60b 1.54c 708c 602b 0.240a 60.4a 56.4a

1 Valuesforaparticularcolumnfollowedbydifferentlettersdiffersignificantly(p<0.05).2 Control (300 g/kg sugar), mixing time 180 min; PB, potassium bromate; AA, ascorbic acid; LCS, L-cystein hydrochloride; NEMI, N-ethylmaleimide; DTE,

dithioerythritol.3 ηB:Apparentbiaxialextensionalviscosity,at50%compression.

Source: AdaptedfromManohar,R.S.andP.H.Rao.Journal of Cereal Science, 25,197,1997a.Withpermission.

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. InterrelatIonshIPBetWeenrheologICal ProPertIesofdoughandQualItyofCooKIes

Rheologicalpropertiesofbiscuitdoughasinfluencedbyingredients,processingconditionssuchasmixing,andadditiveswererelatedtothequalityofbiscuitsbyManoharandRao(2002).Extrusiontime(r=−0.54,p <0.01),elasticrecovery(r=−0.84,p<0.01),apparentbiaxialextensionalviscosity(r=−0.62,p <0.01),consistency(r=−0.73,p <0.01),andhardness(r=−0.68,p <0.01)ofthedoughweresignificantlycorrelated to thespreadof thebiscuits.Elastic recovery (r=−0.64,p <0.01)andcohesiveness(r=0.67,p <0.01)ofdoughmainlyinfluencedthe thickness of biscuits. Extrusion time (r = 0.53, p < 0.01), elastic recovery(r=0.78, p<0.01), apparent biaxial extensional viscosity (r=0.59, p <0.01),consistency(r=0.62,p <0.01),andhardness(r=0.60,p<0.01)werepositivelycorrelatedtothedensityofbiscuits.Amongthevariousrheologicalcharacteris-ticsstudied,elasticrecoverywasreportedtobethebestindexinpredictingthequalityofbiscuits.Similarly,Pedersonetal.(2005)concludedthatshrinkage(r=0.70)andspread(r=0.43)ofbiscuitswerecorrelatedtopercentrecoveryofthedough,andproteinandglutencontent.

. ConClusIon

Doughingredientshadamajoreffectonrheologicalpropertiesandqualityofcook-iesandbiscuits.Increasesinwater,sugar,andfatcontentofcookiedoughdecreasedconsistencyandelasticityandthereforeincreasedspreadofcookiedough.Reduc-ing sugarshada similar effect as increasing the sugar content.Sucrose couldbereplacedbymaltitol,lactitol,orsorbitolinlow-fatcookieswithsupplementationofacesulfate-Kfortheimprovementoftaste.Sugar-freedoughwasmoreelasticthanthesucrosesyrupdough.Emulsifiedfatandmargarineprovidedbetterrheologicalpropertiesthannonemulsifiedhydrogenatedfatandsunfloweroil.Incorporationofhydrogenatedfat to theformulationproducedhardcookiedough.Theadditionofemulsifiers reduced the elasticityof cookiedough.Low-fat and liquid-oil doughsweremoreliquidlike,andfirm-fatdoughwasmoreelasticthanthestandarddough.Substitutingshorteningwith50% to75%canolaoil/caprylicacidstructured lipid(SL)orwithacarbohydrate-basedfatreplacer,NutrimOB(NU)loweredtheelastic-ityofthedough.Anincreaseinproteinandglutencontentincreasedelasticityanddecreasedspreadofcookiesbecauseofglutennetworkformation.Disulfitecleavingagentsandproteaseincreasedextensibilityanddecreasedelasticityofcookiedoughsbyweakeningtheglutennetwork.

referenCes

Agyare,K.K.,Y.L.Xiong,K.Addo,andC.C.Akoh.2004.Dynamicrheologicalandthermalpropertiesofsoftwheatflourdoughcontainingstructuredlipid.Journal of Food Sci-ence69:297–302.

Agyare, K.K., K. Addo, Y.L. Xiong, and C.C. Akoh. 2005. Effect of lipid on alveographcharacteristics,bakingandtexturalqualitiesofsoftwheatflour.Journal of Cereal Sci-ence42:309–316.

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Baltsavias,A.,A.Jurgens,andT.vanVliet.1997.Rheologicalpropertiesofshortdoughsatsmalldeformation.Journal of Cereal Science26:289–300.

Baltsavias,A.,A.Jurgens,andT.vanVliet.1999a.Rheologicalpropertiesofshortdoughsatlargedeformation.Journal of Cereal Science29:33–42.

Baltsavias,A.,A.Jurgens,andT.vanVliet.1999b.Largedeformationpropertiesofshortdoughs:Effectof sucrose in relation tomixing time.Journal of Cereal Science29:43–48.

Faridi,H.1990.Applicationofrheologyinthecookieandcrackerindustry.InDough Rheol-ogy and Baked Product Texture,Eds.H.FaridiandJ.M.Faubion,363–384.NewYork:AVI.

Gaines,C.S.1990.Influenceofchemicalandphysicalmodificationofsoftwheatproteinonsugar-snapcookiedoughconsistency,cookiesize,andhardness.Cereal Chemistry67:73–77.

Jacob,J.andK.Leelavathi.2007.Effectoffattypeoncookiedoughandcookierheology.Journal of Food Engineering 79:299–305.

Lee,S.andG.E.Inglett.2006.Rheologicalandphysicalevaluationofjet-cookedoatbranin low calorie cookies. International Journal of Food Science and Technology 41:553–559.

Maache-Rezzoug,Z.,J.M.Bovier,K.Allaf,andC.Patras.1998a.Studyofmixingwithrheo-logicalpropertiesofbiscuitdoughanddimensionalcharacteristicsofbiscuits.Journal of Food Engineering35:43–56.

Maache-Rezzoug,Z.,J.M.Bovier,K.Allaf,andC.Patras.1998b.Effectofprincipleingredi-entsonrheologicalbehaviourofbiscuitdoughandqualityofbiscuits.Journal of Food Engineering 35:23–42.

Manohar,R.S.andP.H.Rao.1992.Useofapenetrometerformeasuringrheologicalcharac-teristicsofbiscuitdough.Cereal Chemistry 69:619–623.

Manohar,R.S.andP.H.Rao.1997a.Effectofmixingperiodandadditivesontherheolog-ical characteristics of dough and quality of biscuits. Journal of Cereal Science 25:197–206.

Manohar,R.S.andP.H.Rao.1997b.Effectofsugarsonrheologicalcharacteristicsofbis-cuitdoughandqualityofbiscuits.Journal of the Science of Food and Agriculture75:383–390.

Manohar,R.S.andP.H.Rao.1999a.Effectofmixingmethodontherheologicalcharacteris-ticsofbiscuitdoughandthequalityofbiscuits.European Food Research and Technol-ogy210:43–48.

Manohar,R.S.andP.H.Rao.1999b.Effectsofwateron the rheologicalcharacteristicsofbiscuitdoughand thequalityofbiscuits.European Food Research and Technology 209:281–285.

Manohar,R.S.andP.H.Rao.1999c.Effectsofemulsifiers,fatlevelandtypeontherheologi-calcharacteristicsofbiscuitdoughandthequalityofbiscuits.Journal of the Science of Food and Agriculture 79:1223–1231.

Manohar,R.S.andP.H.Rao.2002.Interrelationshipbetweenrheologicalcharacteristicsofdoughqualityofbiscuits;useofelasticrecoveryofdoughtopredictbiscuitquality.Food Research International35:807–813.

Olewnik,M.C.andK.Kulp.1984.Theeffectofmixing timeand ingredientvariationonfarinogramsofcookiedoughs.Cereal Chemistry61:532–537.

Pedersen,L.,K.Kaack,M.N.Bergsøe,andJ.Adler-Nissen.2004.Rheologicalpropertiesof biscuit dough from different cultivars, and relationship to baking characteristics.Journal of Cereal Science39:37–46.

Pedersen,L.,K.Kaack,M.N.Bergsøe,andJ.Adler-Nissen.2005.Effectofchemicalandenzymaticmodificationondoughrheologyandbiscuitcharacteristics.Journal of Food Science70:152–158.

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Sahin,S.,andS.G.Sumnu.2006.Physical Properties of Foods.NewYork:Springer.Steffe,J.F.1996.Rheological Methods in Food Process Engineering.EastLansing,MI:Free-

manPress.Zoulias,E.I.,S.Piknis,andV.Oreopoulou.2000.Effectof sugar replacementbypolyols

andacesulfame-Konpropertiesoflowfatcookies.Journal of the Science of Food and Agriculture80:2049–2056.

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7 Technology of Cake Production

Suzan Tireki

Contents

7.1 Introduction................................................................................................. 1497.2 Mixing......................................................................................................... 150

7.2.1 MixingMethods.............................................................................. 1507.2.1.1 CakeMixing....................................................................... 1507.2.1.2 FoamCakeMixing............................................................ 152

7.2.2 CakeMixingMachines.................................................................... 1537.2.2.1 HorizontalMixers.............................................................. 1537.2.2.2 VerticalMixers................................................................... 1537.2.2.3 MortonPressureWhisk...................................................... 1537.2.2.4 TonelliMixingSystem....................................................... 1547.2.2.5 OakesContinuousMixer.................................................... 1547.2.2.6 MondomixContinuousAerator......................................... 1557.2.2.7 OtherTypesofMixers....................................................... 155

7.3 Depositors................................................................................................... 1557.3.1 CopelandDepositor......................................................................... 1557.3.2 MonoElectronicDepositor.............................................................. 156

7.4 CakeBaking................................................................................................ 1567.4.1 Small-ScaleCakeProduction.......................................................... 1567.4.2 Large-ScaleCakeProduction.......................................................... 157

7.5 Cooling........................................................................................................ 1577.6 PackagingandWrappingEquipment.......................................................... 157References.............................................................................................................. 158

. IntroduCtIon

Itisdifficulttodefinecakesinaprecisemannerduetotheirwidevarietyandthebroadrangeoftheirformulations.Cakeproductscontainrelativelyhighamountsofenrichingingredientslikesugar,shortening,eggs,milk,andflavorsinadditiontosoftwheatflour,andtheyhavesweettaste,atenderandashorttexture,andpleas-ingflavorsandaromas.Cakesmaybegroupedintotwobroadcategories:shorten-ing-basedcakesandfoam-typecakes.Inshortening-basedcakes,crumbstructureisderivedfromthefat–liquidemulsioncreatedduringtheprocessingofbatter.Infoam-typecakes,structureandvolumeareprimarilydependentonthefoamingandaeratingpropertiesofeggs.Sweetdoughproductscanalsobeclassifiedasathird

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group of cakes, which are yeast leavened and involvevariousjams,fruit,nutfilling,andtoppings.

Cake quality is affected by the ingredients used,anappropriateandproperlybalancedformulation,andmixingandbakingprocedures.Inadditiontothese,cor-rectpreparationofhoopsandothercontainersinorderto provide adequate protection during baking, care-fulpreparationofallof the ingredientsbeforemixing(especially with regard to temperature and to fruit ifbeingused),andcarefulbatterhandlingduringscalinganddepositingaretheotherfactorscontributingtocakequality(Desrosier1977;Pyler1988).Ageneralflowdia-gramofcakeproduction is shown inFigure7.1.Cakeproduction includes the steps of mixing, depositing,baking,cooling,andpackaging.

Thischapterfocusesoncakeproductiontechnologyandtheequipmentusedincakeproduction.

. MIxIng

7.2.1 mixinGmeThods

Mixingmethoddependsonwhethershorteningorfoam-typecakeismixed.

... CakeMixing

Bringingaboutacompleteanduniformdispersionandhomogeneousmutualemul-sification of the various ingredients, generally accompanied with the entrapmentandsizereductionofaircellsandaminimumglutendevelopmentinflour,arethemainpurposesof cakemixing.Themixingprocess, takingplace inmixerswithvariousmixeraccessories(Figure7.2andFigure7.3),differsintheorderofingre-dient incorporation,duration,andrateofmixingactionduringdifferentstagesofmultistagemethods,temperatureoftheingredients,andotherfactorsaccordingtothenatureofthecakebeingproduced.

Thecreaming(sugarbatter)methodcombinesshorteningwith thegranulatedsugarandusuallywithsomeofthedryingredientsatslowormediummixingspeeduntil the components are thoroughly blended and the resulting mixture becomesaerated.Thisstepisfollowedbytheincorporationofeggsasthecreamingactioniscontinued.Withaddingmilkandflour,cakemixingiscompleted.Largevolumesofairincorporationintheminusculecellsinthefatphaseofthebatter,coatingoftheflourandsugarbyfat,delayinghydrationandsolubilization,andnearabsenceofglu-tendevelopmentinflourarethemainadvantagesofthecreamingmixingmethod.Thecreamingmethodtakes15to20minwithan8to10mininitialcreamingstage,a5to6minsecondstageofeggincorporation,and5to6minfinalstageofmilkandflouraddition.

Intheblending(flourbatter)mixingmethod,flourandshorteningarecreamedtoafluffymassinonebowl,while,atthesametime,theeggsandsugararewhipped

INGREDIENTS

MIXING

DEPOSITING

BAKING

COOLING

PACKAGING

fIgure. Cake pro-ductionflowdiagram.

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Technology of Cake Production

atmediumspeedtoafoamthatissemifirminasecondbowl.Theseparatemixingin thetwobowlstakesabout10min.Thesugar–eggfoamisnextcombinedwiththecreamedmixtureofflourandshortening,andthenmilkisaddedinsmallincre-ments.Theblendingmixingmethodhastheadvantageofachievingaverythoroughshorteningdispersionthroughoutthebatterandproducinganextremelyfinegrainanduniformtextureinthecake,andthispermitstheuseofhighersugarandliquidlevelsthanispossiblewiththecreamingmethod.However,inadditiontotheusageoftwomixingbowls,thereisasomewhatlessamountofairincorporationwithafol-lowinglossinproductvolumeandamorepronouncedglutendevelopmentcausingperceptibletoughnessinthecakeinthistypeofmixing.

Inthesingle-stagecakemixingmethod,allofthemajoringredientsareputintothemixingbowlatonetimeandmixedintoahomogeneousmass.Thesingle-stagemixingmethodisusuallycomposedof1to3minofblendingtheingredientsintoahomogeneousmixturewithaflatbeateratlowspeed,followedby3to5minmixingatmediumspeedand2minfinalmixingatlowspeed—thetotalmixingtimeis8to10min.Incorporatingthebakingpowderisgenerallydoneduringthefinalmixingstage.

Inadditiontotheabovemixingmethods,severalothermixingproceduresareused.Accordingtoabattermixingmethod,allofthesugarandaboutonehalfits

fIgure. Cakebatterbeater.(Seecolorinsertafterp.158.)

fIgure. Cake batter whip.(Seecolorinsertafterp.158.)

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weightofwaterareputinthebowlandmixedatmediumspeedforabout30sec.Then,emulsifier,shortening,flour,nonfatdrymilksolids,bakingpowder,andsaltare added, and mixing is continued for 5 min at medium speed. The remainingwater,eggs,andflavoringareaddedfinallyandmixedforanadditional1minatthelowspeed.Eitherleaveningamountshouldbedecreasedby25%orthewatershouldbeincreasedby15%becausethismethodpromotesgoodaeration.Cakesproducedwith thismixingmethodarestated todevelopabettercrustcolor,amore tendercrustwithlessindicationofundissolvedsugar,andgreatervolume.Thecakequalityimprovementmightbeduetotheinitialsolutionofthesugar.

The sugarandshorteningarecreamed together for2 to3min intoa smoothmassintheemulsionmixingmethod.Thismixingmethodisespeciallysuitedforlarge-volumecakemixers.Then,themilkisaddedinseveralportionswithcontinu-ousbeatingforabout5minatmediumspeed,andfollowingthis,theflourisaddedover2minandtheeggsareaddedandmixedforanadditional4to5min.Thetotalmixingtimeoftheemulsionmethodtakes12to15min.

Fluidcakeshorteningsimprovecakemixingefficiency.Thismightbeduetothegreatereaseofdispersionoffluidfatinboththedryandliquidbatteringredients,andpartlyduetoitsmoreeffectivelubricationofthemixingbowlwalls,reducingtheneedfortheirfrequentscrapingdown.Inaddition,inclusionofneweremulsifiertypesintheshorteningprovidesfasterairincorporationinthebatterandpermitsthereadyemulsificationofhigherlevelsofliquids.Allthementionedfactorscontributetoadecreaseinthemixingtimewithrespecttotherequirementsinthecaseofplas-ticshorteningusage.

... foamCakeMixing

Thestructureandvolumeoffoamcakesaredependentontheabilityofeggsintheformulationtooccludeairandtoformstablefoams.Aseggwhiteisbeaten,airisincorporated,andtheaircellsbecomesmallerinanincreasingmannerasbeatingiscontinued.Theeggfoamstabilityisdependentonthebeatingtime,withmorestablefoamsbeingformedasthetimeisextended.Thebeatingtimeisaffectedbythebeat-ingconditions,suchaseggtemperature,beatertype(whetherofthewirewhiporthebladebeatertype),beatingspeed,andsugaradditiontime.

Themixingofspongecakebattersmaybeconductedinseveralways.Some-times,peopleprefertoseparatethewhitesandyolksofeggsandwhipthemsepa-ratelywithaportionofthesugartothedesireddensitypriortotherecombinationof them.Thepurposeof thisapproach is toobtainmaximumbattervolume.Thebeatingofeggs(tempered toa temperatureofabout26.7°C)withawirewhiporbladebeateratmediumspeedisthemostcommonprocedure.Sugarmaybeaddedattheoutsetofmixingorinaslowstreamduringbeatinginordertocounteractthetendencyofwhitestooverwhip.Aftertheeggfoamattainstheproperdensity,theflour and the liquid are folded in as lightly aspossible toprevent foamstructurebreakdown.Fatmustbeaddedatthefinalmixingstageinordertominimizethelossinvolumeinshortspongecakes.

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7.2.2 CakemixinGmaChines

Therearemanytypesofequipmentforthepurposeofcakemixing.Thesearehori-zontalmixers,verticalmixers,Mortonpressurewhisk,Tonellimixingsystem,Oakescontinuousmixer,Mondomixcontinuousaeratingequipment,OakesandStrahmannmixersforpastes,high-speedmixers,TweedymixerandMono,Cresta,Stephan,andGilbert(Bennionand Bamford1997).

... horizontalMixers

Horizontalmixersareofverystrongconstruction,andthetroughsofthistypeofmixeraresoarrangedthattheingredientscanbereadilyputinanddischarged.Thebeatersaredesignedformixturescontainingbutterorshortening,mixingintothemassofanyingredientsorfruitwithoutdamage.Anautomaticsafetylidisfittedtothemachineaspartofthestandarddesigninordertoavoidthemachinebeingopenedwhileinmotion.Twospeedsareavailableinhorizontalmixers,highspeedformixingthelightbatterandslowspeedformixingtheflour,fruits,andsoforth.

... verticalMixers

Vertical mixers have been developed for all mixing types in the bakery (dough,batters,andspongesandfoams).Threeorfourspeedsareavailable,changinggearis easy, and automatic timing devices are also fitted. The bowls of vertical mix-ers are safe during the time the machine is used, and they can be detached andremovedfromthemachineeasilyeitherbyplacingonanappropriatetrolleyorbymanhandling.Theequipmentisfittedwithwhisksforspongework,withbeatersforcakebattersanddoughhooksforbreadorbundoughorforpastry.Thebeatersandwhisksrevolveinaplanetarymotioninordertoscrapethesidesandthebottomofthebowl.Anautomaticscrapingapparatusisprovidedinsomemodelsinordertokeepthesidesofthebowlcleanduringthemixingprocess.Variable-speedmotorsarefittedinsomemodelstoeliminatethegearbox,whereasothermodelshavethree-speed,constant-mesh,preselectivegearboxeswithcompleteautomaticlubrication.

... MortonPressureWhisk

Thismixertypewasusedalmostuniversallyforlarge-scaleproductionofspongegoodsuntiltheintroductionofcontinuousmixing.Ithasbeenreplacednowinmod-ernproductionplants.However,itisstillusedasapremixerlinkedtothecontinuousmixer.Thismixertypeisstillusedinsemiautomaticplantsforspongework.IthasaMortonwhisk in thecentercontainerand twohoppers,oneateachside,wheretheeggsandsugararefedintothemixingcompartment.Twohoppersarepresentinordertopreventthewettingofsugarandhencepreventastoppageinthehopper.Thelarger-scaleequipmentismotordriven,andthereisanaircompressor.Itisnotrequiredtoremovetheliduntiltheendofthedaywiththismixertype.Thecompres-sorhasanautomaticregulatorbeingsetandlockedinordertoensurethatthepres-surewillnotincreaseabovethatneededtoworktheequipment.Asafetyvalveontheairreceiverandaspecialtypeofsafetycockonthemachinearealsofitted.Forobservingtheworkingpressure,pressuregaugesarefittedonallmachines.There

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isapiston-typeejectoratthebottomofthecontainersothattheairpressureinthecontainerejectsthebatterintoabowlormixingmachineasneededwhenthevalveisopened.ByusingaMortonpressurewhisk,aspongebattercanbeproducedin3mininsteadoffrom15to30min,andthespongeobtainedhasaveryfine,eventextureofgreatuniformity(Bennionand Bamford1997).

... tonelliMixingsystem

TheTonellimixingsystem,whichisnotacontinuoussystem,isstatedtobethefirstbatch system to integrate completelywithbulk systemsandprogrammablecontrol. It isauniquemixingsystemusinga twin-toolvariable-speedplanetarymixing action said to be able to cut mixing times up to 75%. A constant bowlscrapercanbeinvolvedinthismixingsystem,anditcanmixcreams,cakebatters,anddoughwithsuitablechangeofmixingtools.Thesealedmixingbowlpermitsmixingunderpressure,andajacketedbowlisavailableforcoolingorchillingdur-ingmixing.Manymixingtoolsareavailablefromvariouswhisktypesforcreamsandfoams, lightandheavybatters, inadditionto thetoolsforpie,shortpastry,andcookies.

... oakesContinuousMixer

Oakescontinuousmixersareusedfortheproductionofalltypesofconfectionery.Themixingheadistheoperationalpartofthemachine,andtheingredientsarefedintheformofliquidbattercontinuouslywithanairstreamintothebackstatorofthemixingheadwheretheythenfollowinradialdirectionoutwardtotheperiphery,andthenflowinradialdirectioninwardalongthefrontstatorpriortobeingdischargedthroughtheoutlet.Therotorspeedandthedistributionofteetharearrangedinawaythatgivestheoptimumintensityforaparticularproduct.Apressure-regulatingvalveislocatedattheoutletenablingthepressureinthemixingheadtoberegu-lated toensure that theairbubblesare incorporatedcompletelywithin the liquidbatterbefore themixture is released through thedeliverypipe.Themixingheadisequippedwithcoolingjackets;however,thetemperatureincreaserarelyexceeds−16.7 to −16.1°C due to the fact that the material is only in the mixing head forseconds.Themixingdegreeattainedproducesacompletelyhomogeneousproductwheretheairisdisperseduniformly;hence,thefinishedproducthasuniformcellstructureandtextureandgoodkeepingqualities.Theoperationmethodgenerallyusedinmixingcakebatteriscomposedofdumpingalltheingredients(wetanddry)intothebowlofabatchmixer,mixingfor1to3mintodispersethematerialswithintheliquidbatteruniformly,andtransferringittoaholdingtankthatisadjacenttothemixer.Bygravity,theliquidbatterflowsfromtheholdingtanktotheproductpumpsuctiononthemixer,andthisdeliversthematerialthroughapipelinetothemixingheadunderpressureandthentothedepositor.Itispossibletocontrolthespeedoftherotor,speedofthepump,backpressure,theamountofair,andthethroughputofthemixing(Bennionand Bamford1997).

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... MondomixContinuousaerator

AdosedamountofairisinjectedontheinputsideofthemixingheadofMondomix.Therotorandstatorpinsthencuttheproductandtheairunderconstantpressureuntilahomogeneousmixtureisobtained.Amassairflowmetercombinedwithanautomaticairdosingsystemmakes thefoamdensityremainconstant.Mondomixsupplycompleteproductionunitsincludingmanifolds,rotatingandstaticextruders,depositors,andallotherequipment.

... othertypesofMixers

OakesandStrahmanncontinuousbreadmixingequipmentisusedforthecontinu-ousproductionofshortpasteforpiesandtarts(Bennionand Bamford1997).

High-speedmixerswereoriginallyintroducedforbreaddoughmixingpurposes,butwerethenadaptedforuseinmixingcakebattersandpastes(Bayliss1967).

TheTweedymixerhasbeenadaptedforallcake-makingtypes.Alloftheingre-dientsareputinthemixingbowlatonce,andmixingiscompletedinvarioustimesdependingonthetypeoftheproduct(e.g.,mixingiscompletedin1minforslabcakes,whereasin3.5minforangelcake).Inaddition,whentheTweedymixerisused,novacuumisneededincakeprocessing.

TheMonomultipurposemachine,Crestamachine,andStephan(forsmallermix-ing)machinearesimilarequipmenttotheTweedymachine.TheGilbertmachine,whichisanultra-high-speedmixer,differsinasmuchasthebowlsareremovableandtransferable.Alltypesofgoodscanbemixedwithouttheneedtochangebeaters.

. dePosItors

Cakebatter shouldbedeposited into cakepans andconveyed to theovenwith aminimumtimeloss.Thisisduetothefactthattheleaveningagents,havingenteredintosolutionduringmixing,begintointeractandevolvecarbondioxidegas.Inmorefluidbatters,carbondioxidegastendstoriseupwardwiththesmallbubblescoalesc-ingintheprocessintolargercellshavinggreaterbuoyancy.Thereisaninevitablecarbondioxidegasescapefromthebatterwhilerestingintheopenhopperofthedepositor,aswellasacoarseningofthecellstructurewiththepassageoftime.Thisaerationlossandassociateddetrimentaleffectsareavoidedwithdepositors.

There is a wide range of equipment for the purpose of depositing accuratelypredeterminedquantitiesofmixes(Bennionand Bamford1997).

7.3.1 CoPelanddePosiTor

TheCopelanddepositorhandlesanymixexitingfreelyfromthehopperundertheeffectofsuctionfromthedepositorplunger.Itispossibletodepositawiderangeofmixesfromlightspongetoheavyfruitcake.Thisdepositortypeinvolvesahopperanddepositingheadarrangedtogivealiftmotiontobreakthedeposit.Theheadcanbestationaryifthereisawirecut-offalternatively.Sheetsortinsaretransportedtoapositionunderthedepositingheadbyanintermittentchainconveyor,andthere

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isfasthandwheelchangeoverontheconveyorwhenchangingfromonepansizetoanother(Bayliss1967).

7.3.2 monoeleCTroniCdePosiTor

Monoelectronicdepositorsareveryflexibleandpopular,andtheyareideallyappro-priateformanysingleandmixedapplications.Therecipe,mixingmethod,sizeoftemplate,andspeedofdepositareseveralfactorsaffectingtheminimumdeposit.Alloftheelectronicsofthisdepositortypearemicroprocessorcontrolled,andaninstantprogramchangecanbedonewithasimpletwo-digitcodeforeachproduct.Avarietyoftemplatesareavailableinvariousconfigurationsfromtwototennozzles.Therearealsoclusterandnoveltyheads,andaheatedhopper isused inorder tomaintainoptimumtemperaturesoffondantandicings.

. CaKeBaKIng

Bakingisprobablythemostimportantfactorgoverningthequalityofthefinalcakeproduct. Incorrectbakingcanoffset theeffectofall theother factors likecorrectformulations,goodrawmaterials,andcorrectprocessingmethods.Allofthecakesshouldbebakedatasuitabletemperature,consistentwiththenatureoftheingredi-entsandtheshapeandsizeofthecakes.Aleanmixinghavingfewenrichingagentsshouldbebakedatamuchhighertemperaturethanamixveryrichinfats,sugars,fruits, and syrups.Anoven that is toohot causeshigh crust color, small volume,peakedtops,closeorirregularcrumb,andprobablyallthefaultsbecauseofunder-baking.Ontheotherhand,anoventhatistoocoldcausespoorcrustcolor,largevol-ume,andoftenweakcrumb.Theoptimumcake-bakingconditionsaredeterminedbyseveralfactorssuchaslevelofsweetenerintheformulation,milkamountinthebat-ter,batterfluidity,pansize,andsoforth.Batterswithhighsugarcontentneedlowerbakingtemperaturesthanleanerformulations.Largecakesrequirelowerbakingtem-peraturesand,hence,longerbakingtimes.Thebakingtimeisinverselyrelatedtothebaking temperature.Baking timeshouldnotbeextendedbeyond the limitneededto ensure a thorough bake, because otherwise, the evaporative losses will exceedacceptednorms,andtheshelflifeofthecakewillbeimpaired(Pyler1988).

7.4.1 small-sCaleCakeProduCTion

Small-scalecakeproductionworksonthebasisofthebakingofcakesrequiringthehighest temperature first, working through to those requiring lower temperaturesandlongertimeattheendoftheday’srun.Thisapproachcomesfromthedayswhenlargecoke-orcoal-firedbrickovenswerecommonlyused.Theseovenswerenotsoflexible;however,theywereveryreliableandmanybakeryproductswerebakedbyresidualheatonafallingtemperature.Thisisstillidealformanycaketypes(Ben-nionand Bamford1997).

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7.4.2 larGe-sCaleCakeProduCTion

Arranging output in such a way as to allow long runs of a single product is thetendencyoflarge-scaleproductionoftoday,whichmakesforhigherefficiencyandbetter control of the oven. Many big manufacturers still require a multipurposeplant;hence,ovenscontendingwithamixedrangeofproductshavevariablebakingrequirements(Bennionand Bamford1997).

Large-orsmall-scalecakeproductionneedsmaximumovenusage,andbatchesandproductionrunsshouldbeofsuchasizetoachievethisifitistobeeconomical.Ahalf-emptyovenoranovennotinuseforlongtimeperiodsisveryuneconomical,andfurthermore,thebakingofcakesisbetterwhentheovenisfull.

. CoolIng

Coolingiscrucialincakeproductionintermsofthefinaltextureandappearanceoftheproducts.

Automaticcoolersmaybeemployedinsomecakeproduction.Automaticcool-ersaretravelingcoolersandcanbebuilttohaveeitheroneortwoswingssuspendedfromchains,andtheyaredrivenbyasmallmotorincorporatingavariable-speeddevicefortheregulationofcoolingtimesfordifferentproducttypes.Outputdependsonthecoolersize.Naturaloropenaircoolingisgenerallyused.Ontheotherhand,conditionedaircanbeusedifthecoolerhasatotallyenclosedmainstructure.Cool-ersarevaluableforcakeswhenbakedontrays,becausecoolersenabletheproductstocooloffpriortofinishingandpackaging,andhencetheyeliminatecongestioninthebakery.Moreover,coolersreducethewearofthebakingfloor.Inaddition,cool-ersdonotneedtohavethefeedandthedeliverypointsatthesamelevel.Actually,thecakescanbeplacedinthecooleronanyfloorwheretheovensmaybelocatedanddeliveredatthegroundfloororsuitablelevelofthedispatchdepartment.

. PaCKagIngandWraPPIngeQuIPMent

Mechanicalwrappingmethodshavebeenimprovedwiththeadvancestakingplaceinthesaleofprepackedcakes.ForgroveBW6andBW-6PuniversaloverwrappingmachinesandtheForgrove84-Harethemostpopularwrappingmachinesusedincakeproduction.TheBW6andBW-6Pare simple, adjustable equipment and aresuitableforawiderangeofcakesandcartonsofcakes.Theprinciplepropertyistheself-measuringpaperfeed,givingsubstantialsavingsinwrappingmaterials.Inthe84-Hmodel,thewrappingmaterialisformedintoatubearoundthearticleinsidea folding box. Then, rotary crimpers form the cross seals, and the packages areseparatedbyintegralknives.Thiswrappingequipmentisversatileandusesawiderangeofwrappingmaterialswithspecialattachmentsforsealing,printing,andtypecoding,anditcanwrapfrom40to100packagesperminutedependingonthecaketype(Bennionand Bamford1997).

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referenCes

Bayliss,E.A.1967.Automaticcakeproduction.ASBEConferenceProceedings,Nov.17–25.Bennion,E.B.andG.S.T.Bamford.1997.The Technology of Cake Making.London:Blackie

AcademicandProfessional.Desrosier,N.W.1977. Elements of Food Technology.Westport,CT:AVI.Pyler,E.J.1988.Baking Science and Technology Volume II.Meriam,KansasCity:Sosland

PublishingCompany.

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8 Technology of Cookie Production

Suzan Tireki

Contents

8.1 Introduction................................................................................................. 1598.2 ProductionProcesses.................................................................................. 159

8.2.1 Dough-MakingProcessandMixers................................................ 1598.2.1.1 Dough-MakingProcess...................................................... 1608.2.1.2 Mixers................................................................................. 162

8.2.2 ProcessingandShaping................................................................... 1638.2.3 Baking.............................................................................................. 165

8.2.3.1 BakingPrinciples............................................................... 1658.2.3.2 ChangesinDoughduringBaking...................................... 1668.2.3.3 Ovens.................................................................................. 168

8.2.4 Cooling............................................................................................. 1708.2.5 PackagingProcessandEquipment.................................................. 170

References.............................................................................................................. 172

. IntroduCtIon

Cookies(Figure8.1)maybedefinedassmallcake-likeproductsfromadoughorbatter made from raw materials such as flour, fat, sugar, milk, eggs, salt, starch,cocoa,leaveningagents,emulsifier,andessences,whichisviscousenoughtoallowthepiecesofdoughtobebakedonaflatsurface.Theycomeinaninfinitevarietyofsizes,shapes,texture,composition,tenderness,tastes,andcolors(Pyler1988).AgeneralflowdiagramofcookieproductionisshowninFigure8.2.

Explained in this chapter will be different cookie-dough-making methods,mixertypes,doughprocessing,bakingandovens,coolingofcookies,andtheprod-uctpackagingprocess.

. ProduCtIonProCesses

8.2.1 douGh-makinGProCessandmixers

Cookies are generally categorized according to the equipment used in their pro-ductionascutting-machinecookies,rotary-moldedcookies,wire-cutcookies,bar-machinecookies,anddepositedcookies(Desrosier1977).

Theequipment typeused limits therheologicalqualitiesofdoughandhencethecomposition.

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... dough-MakingProcess

Thedough-makingprocessdependson the typeof thedough.The fat and sugarcontentsofcutting-machinedougharelow,buttheirwatercontentishigh.Astheformationof theglutennetwork isdesired in cutting-machinedough, themixingdurationislong.Themixingperiodcanbereducedbyusingsodiummetabisulfiteoracommercialprotease.Duringmixing,theproteininflourcontactswithwaterandinthefollowingstepsittakestimefortheproteintoabsorbwaterandswell.Ifmixingiscontinued,theproteincontainingwaterformsathree-dimensionalglutennetwork.Forcutting-machinedough,alltheingredientsareputintothemixeratthesametime,andthedurationofmixingislongasstatedbeforebecauseformationofaglutennetworkisdesired.Thesugarshouldbedissolvedbythewaterinthedough.Otherwise,thesugarcrystalscaramelizeduringbaking,causingbrownspots.Thetemperatureofthedoughisimportantintermsofthefatused.Athightemperatures,fatmeltsanddoughbecomesfatty.Doughshouldbeplastic,and theshapegivenshouldbemaintained.

Inrotary-moldeddoughs,theamountofsugarandfatishigh,andtheamountofwaterislow(sugar:20to45%,fat:10to40%,water:5to15for100%flour[flourweightbasis]).Thiskindofdoughcanbecrumbledeasily,thematurityofglutenisundesired,andhencemixingdurationisless.Therearetwostepsinrotary-moldeddoughpreparation:

1.Creaming(premix)step 2.Additionofflour

In thecreamingstep,all ingredientsexceptflouraremixedandconverted tocream.Thecreamingstepshouldbeprolongedasmuchaspossible,whichplaysacrucialroleinthedensityofdough.Thesecondstepofdoughpreparation,theaddi-tionofflour,takesashorttimeasformationofaglutennetworkshouldbeprevented.Ifthedurationofmixingislonger,glutennetworkformationstartsandthedough

fIgure. Cookies. (Seecolor insertafterp.158.)

fIgure. Cookieproductionflowdiagram.

BAKING

COOLING

PACKAGING

PROCESSING&

SHAPING

DOUGH MAKING

FAT SUGAROTHER INGREDIENTSFLOUR

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Technology of Cookie Production

willgainelasticity.Asaconsequence,areductioninvolumewillbeseenindoughduringleavingofthemolds.Inthecreamingstep,sugarisdissolvedandfatissoft-ened,sotheysurroundtheproteinmoleculesinflourandthispreventstheinterac-tionwithwater,andtherefore,theformationofaglutennetworkismoredifficultandslow.Fatisthemostimportantinputbecauseitbindstheingredientsinrotary-typedoughs.Unlessthedoughismixedenough,itcannotbeshapedandexitfromthemoldwillbedifficult.

Thecompositionofwire-cutcookiescanbevariedoverawiderrangeintermsofformulationandfinalshapethananyothertype.Inthesedoughs,itisrequiredtohavethematerialcohesiveenoughtoholdtogetherasitisextrudedthroughanorifice,butitmustnotbestickyanditmustbesufficientlyshortsothatitseparatescleanlyas it iscutbywire(Pyler1988).Wire-cutcookiedough is fattyandsoft.Itswatercontentishighandcrystalsugarisgenerallyusedforthistypeofcookiedough.Thedevelopmentofgluten isavoidedstrictly,and thedough ismixedforabout2.5to6min.Waferdoughscanbeincludedinthewire-cutvarieties.Waferdoughshaveverylowfatandsugarcontent.Waferdoughisafluiddoughhavingemulsionpropertieswithhighwatercontent.Itcontainsabout35to40%drymateri-alsand90%ofthedrymaterialsconsistofflour.Themainfunctionofthemixingprocess is to obtain a homogeneous mixture. Gluten development and formationofathread-likestructurearenotpermittedinwaferdough.Themixingperiodisabout5min.Ifthread-likestructuresareseen,thedoughisnotpumped,asitcauseschoking,andthedoughdoesnotspreadonthewafermoldwell.Thetemperatureisasimportantastheamountofwateradded.Ifthetemperatureofwaterishigh,themoistureproblemcomesout.

Abar-machinecookieisarelativelyrich,highlyflavoredsoftcookie-typeprod-uctthatisprocessedinasimilarmannertothatofwire-cutcookiesexceptthatbar-typecookiesareofrathersoftdough.

Thebattersofdepositedcookiesareverysoftandlackingcohesiveness.Cream-ingupfat(orotherfats)withthesugar,eggs,milk,andwaterandaddingtheflourlaterwithquiteashortermixingtime(toachievehomogeneity)isusuallybest.Thetemperatureofthedoughiscrucialinordertomaintainrequiredorhigherconsis-tencyandcorrectdispersionoffat.Coolingtheflourmaybeneeded,andanywaterormilkusedshouldbeverycold.Atemperaturerangeof10to16°Cshouldbeaimedatfor thedough.Inaddition to theminimumamountofwater,minimummixingwithflourisalsorequiredbecauseofthefactthatthetoughdoughmustbeavoided(Manley2000).

Flourstrength,producttype,machinabilityofdough,doughtemperature,mixerspeed,andbatchsizearethemostimportantfactorsaffectingthemixingtimeforallofthecookietypes.Theingredientsthatareintendedtobepresentinthefinishedproductasvisiblepieceslikenuts,raisins,andchocolatebitsshouldbeaddedattheendofthemixingcycleandblendedatslowspeedfortheminimumtimeconsistentwithenoughdistributionthroughoutthedough.Althoughdoughsthataretoocoldcancausemachiningdifficulties,hightemperaturedevelopedduringmixingistheusualproblem.Inanycase,uniformtemperaturesarecrucialformakinguniformcookies as dough temperature affects spread, texture, and surface appearance of

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thecookie.Thetemperatureshouldbebelowtheupperlimitoftheplasticrangeofshorteningforthebestresults.

... Mixers

Mixingorblendingcanbeperformedbymanydifferenttypesofequipment,butallofthemrelyononeormoreofthefollowing;

1.Pushingpartsofthemixturethroughotherpartsbyblades,paddles,helicalmetalribbons,etc.

2.Elevatinganddroppingallorapartofabatchsothatrandomreboundingofindividualparticlesresultsinredistributionoftheparticles

3.Gasorliquidinjectingcurrentsintoanonuniformmaterialbodyinordertocreateturbulentmovementofparticles.

Cookiedoughispreparedwiththehelpofbigmixers.Mixerscanbeclassifiedashorizontal-fixedbowlandtiltingbowl(highspeed,lowspeed),vertical,reciprocat-ingagitator,andcontinuous(agitator-in-tube,rotorandstatorheads).

Horizontal mixers are useful for a wide variety of doughs from sugar waferbatterstoextremelytoughordrydough.Whenglutendevelopmentisrequired,thismixertypeisessential,becauseverticalmixersaretooinefficientandslowforthispurposeandspindlemixerslackthecorrectkindofaction.

Fordischargingthedough,twomethodsareemployed.Thebowlcanbetiltedandhencethetopisbroughttoaforward-facingpositioninsomemodels.Inothermodels,thereisatightlyfittingdooratthefrontofthebowlthatcanberaisedandloweredindependentoftheimmobilesectionofthebowl.

Mixerbowlsaregenerally jacketedanda refrigerantcanbecirculated in thejackets.Somejacketsareequippedinordertousedirectexpansionofcoolingrefrig-erant like Freon-12 or ammonia, others use cooling liquid like propylene glycol,brine,andwater.

Therearevariousformsofagitators.Onesetoftwo,three,andfourcylindri-calbars,paralleltothefrontofthemixer,maybemountedonspidersconnectedtotheaxlesatthepointwheretheyenterthejacketinthehigh-speedmixersthataredesignedfordevelopinggluten.Thesearmsmaybeattachedbybearingsinordertomakethemrotate,ortheymaybeaffixedinarigidmanner.Thedoughmassisstretchedrepeatedlyandkneadedinasingledirectionsothatglutenfiberstendtobeorientedandthedoughdevelopsduetothelimitedclearanceofthejacketwall.Slow-speedhorizontalmixershavevariousformsofagitatorsandmaybeequippedwithoneortwosetsofaxles.Themixerarmconfigurationandthespeedaffecttheaction.Forstifferdoughs,double-armedmixersareused;however,theymayrequireheaviermotorsanddrives.

Theuseofmovablebowlsortroughsistheunifyingfeatureofverticalmixers.Theotherpropertiesmaybequitediverse.Theremaybeoneormorebeatershaftsthatmaybestationaryormoveinaplanetarydesign.Inaddition,agitatordesigncanbevaried.

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Theagitatormovementisdescribedasplanetarybecauseitrevolvesarounditsownverticalaxisatrelativelyhighspeedand,atthesametime,theaxisalsomovesincirclesasitisrotatedaroundthebowl.Thesecombinedmovementsguaranteethatthemixerbowlatthebottomcenterisraised.

Spindlemixersaremostoftenusedforcrackerdough,althoughtheycanalsobeusedforcookiedough.Theyhavefewadvantagesforcookiedough.Themainadvan-tageforsaltinedoughisduetoitsadaptationtomixinginthespecialtroughthatismobileforfermentingsponges.Duetothispurpose,doughandspongesdonothavetobetransferredinandoutofthemixerandtroughbetweenthevariousstages.

Inreciprocatingagitatormixers,apairofagitatorarmsmovesthroughintersect-ingelliptical-shapedpathsinashallowandslowlyrevolvingbowl.Temperaturescanbeheldnearroomtemperaturewithouttheuseofbowljacketsduetotherelativelyslowrateofenergyinput.Ifanintensiveblendingactionisnotneeded,thesetypesofmixersareusefulinmixingtemperature-sensitivedough.Forequivalenttimes,adjunctbreakdownislessinthesetypesofmixersthaninanyothertypes.

Theingredientsmustbemeteredoutofabulksupplyandfedatasetrateintothemixingzoneinacontinuousmannerfora(timed)continuousmixingsystem.Airoranothergasmaybeoneofthecomponents.Batchpremixesareusedbymanysetups.Singleormultipleunitsmaybeused.Forcakebatters, themixerscomposedofahigh-speeddisc-shapedrotorintermeshingwithdisc-shapedstatorsareusedwidely,andthisequipmenthasbeenadaptedforuseoncookies.Continuousmixingwouldbepossibleforstiffmixtures,yetadifferentkindwouldberequired.

TheOakescontinuousautomaticmixercanbeused formixingwaferdough,batters,andmarshmallow.Themixingchamber iscomposedofa rear stator, therotor,andthefrontstatorandthetwostatorsareboltedtogetherandsupportedontheframe.Theyarefurnishedwithbladesprojectingintothechamber,andtherotorfitsbetweenthestatorsandismountedonarevolvingshaft.Bladesontherotormeshwiththebladesonthestators,andthespeedcanbevariedoverawiderange.

Incontinuousmixers, theproducts tobemixedareforced into theheadbyapositivedisplacementpumpthroughanorificeatthecenteroftherearstator.Theproductsthenflowbetweenthebladesoftherearstatorandtherotortotheoutercircumferenceofthestatorcavity.Themixtureflowsbetweenthebladesofthefrontstatorand the rotor to thedischargevent locatedat thecenterof the front stator.Controls,motorandgeartrain,powersupply,andthenecessarypumpsandpipingaretheremainingpartsofthemixer.Fortemperaturecontrol,themixerheadcanbejacketed.Therevolvingelementimpartsintensesheartothecomponentsofthemixture, creating a turbulence thatquicklymixes them.Gas canbedispersed inliquidsreadily.

8.2.2 ProCessinGandshaPinG

Rotarydoughshouldbegiventothemachineregularlyinordertopreventaccumula-tionattheendscausingdryingofthedough.Rotarydoughisprocessedbytheuseofmoldsindentedtotheinside.Metalcylinder,moldcylinder,andrubbercylindershouldbeparalleltoeachotherinallaxes.Theprocedureappliedbythemoldcylin-dertotherubbercylindershouldbesufficientforthecookiestostickontheinfinite

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cloth.Otherwise,wearingoccursonthemoldandrubbercylinderandhenceshapedisorderscanbeseenonthecookies.

Themost importantstep inprocessingcutting-machinedoughis the thinningofdough.Thereshouldbemorethanonethinnercylinder.Ifdoughisnotpassedthrough twoor three thinningcylinders,hardening in thedoughconsistencyandproductionofdefectivecookiesareobserved.

Afterleavingthesqueezingcylinder,thedoughispassedthroughtwoorthreethinningcylindersinordertoobtainathinlayerofthedough.Whenthisprocessisfinished,thedoughisconvertedintotwotosixfoldsandpassedthroughtwoorthreecylindersagain.Thisprocessiscalledlamination.

Theaimsoflaminatingaretoprovideawaytorepairapoordoughsheettendingtobepreparedwithasimplepairofrolls;toturnthefoldeddoughthroughwithanangleof90°inordertomakethestressesmoreuniformintwodirections;toworkongluten,makingitmoresuitableforbakingwithrolling,folding,andfollowingmorerolling;andtomakeaflakystructureafterbakingwiththeadditionofanothermaterialsuchasfatbetweenlayersofdough.

Averticallaminatorwithacontinuouslapperandaone-sheeter,verticallamina-torwithacontinuouslapperandtwosheeters,horizontallaminators,andcut-sheetlaminatorsarethetypesofautomaticlaminators(Manley2000).

Moldsthatareindentedoutwardsareusedforcutting-machinedoughs.Doughsgetthedesiredshapebetweenthemoldandtherubbercylinder.Crumbeddoughisreturnedbacktothesqueezingcylinderbymechanicalways.

Infiniteclothisthefirstclothafterthemold.Cookiessticktoiteasily,anditisimpossibletotakesamplesfromhere.Thestickingisprovidedbyapplyingvaportothecookies.

Dough for processing on deposit, wire-cut, and bar machines varies in thedegreesofsoftness,whichare

1.Verysoft:Abatterneedstobedepositeddirectlyontothesteelovenbandinvariably.Awire-meshovenbandisnotsuitableforbakingdepositgoods(depositmachine).

2.Softandusuallysticky:Needstobeextrudedandcutbyatautwirepriortobeingdroppedontoacanvasbeltcarryingthedoughpiecestotheovenband.Directcutontotheovenbandisusedinsomecases(wire-cutmachine).

3.Fairlysoftbutstifferthantheseconddegreeofsoftness:Extrudedinend-lessstripscutintosuitablelengthswithareciprocatingguillotine,onacan-vasbeltconveyingtotheovenband(barmachineorroutpressmachine).

Inadepositmachine,whichextrudesbatterintermittentlyfromahopperthroughshapednozzles,itisnecessarytohaveacut-offmechanismthatisincorporatedinthefeedhoppertoensureacontrolledflowanddeposit,becausetheverysoftdoughhasafairlyviscousmovementwithitsowngravitationalflowduetoitsrelativelyhighliq-uidcontent.Thedepositnozzlesareconnectedtothefeedhopperoutletswithflexibletubes,henceallowingapatterneddeposittobemadeinsometypesofdepositors.

Wire-cut machines are more complex when compared with deposit and barmachines,astheyinvolveadevicecuttingoffextrudeddoughpiecesemergingfrom

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thedieorifice,andacut-offdeviceiscomposedofabladeorawiredrawnthroughthedoughfastbyaharpmovingbackandforthbelowtheorifice.Doughisfedtothehoppermanuallyorbygravityfromaholdingtrough.Verticalseparatorplatescanbeinsertedinthehopperinordertomakethefeedingoftwoormorecolorsorflavorspossibleatthesametime.Forauniformpressureandconstantextrusionrate,itiscrucialtokeepthefeedratesteadyandtomaintainhoppercontentsataboutthesameheightatalltimesasinitialsteps.Hoppersarejacketedandwarmairorwateriscirculated for the improvementofextrusion rateuniformity.Hoppers’endsarecurvedinordertodecreasethedoughtendencyofstagnatinginthisarea.Maintain-inguniformweightandsizeinthefinishedcookiesdependsonthepropertiesoftherollerspressingdoughthroughthediecups.Thedelaybetweenmixingandforminginfluencesthecookiedoughresponsetoforming.Itisimportanttoprocessbatchesquickly,andtoformauniformscheduleandfollowitinordertoavoidnoticeabledifferencesinsize,weight,andappearanceofthefinishedproduct.

Asthereisnoneedtoseparatethedoughintocookie-sizepartsattheextruder,barmachineshaveasimpleformingmethod.Continuousstringsordoughstripsontotheovenbandaredirectlyextrudedbybarmachines.Thesebandscanbeseparatedintoindividualbarspriortoorafterbakingwithusualcuttingdevices.Whenthedieplateisinclinedintheextrusiondirection,theribbonissupportedforalongertime.Thisdecreasesbreakingorthinningofthedoughstrandbecauseofthegravitationalpull.Dieorificesofbarmachinesaregenerallywithstraight lower-edgeslots forgivingaflatbottomtothecookieandwithgroovedtop-edgeslotsforgivingaribbeduppersurfacetothecookie.

8.2.3 BakinG

... BakingPrinciples

Cookingcanbedescribedas theartofpreparing foodsbyheatinguntil theyarechangedinflavor,appearance,tenderness,andchemicalcomposition.Bakingisaformofcookingperformedinanoven(Desrosier1977).

Everybakingprocessdependsonheattransferfromonebodytoanotherinthedirectionfromhottocold.Therearethreemodesofheattransfer:conduction(insolidsor liquidsatrest),convection(in liquidsorgases inastateofmotion),andradiation(whichdoesnotinvolveamaterialcarrier).Inadditiontotheovendesign,theconformationofthedoughpieces,size,shape,andcontainerconstructionmate-rials,pan,orband,anddoughpiecesdistributiononthehearthaffect therelativeeffectivenessoftheseheattransfermodes.

Conductionentailsadirectclosecontactbetweentheheatsourceandthemate-rialbeingheated.Ifthedoughisbakedinabandoven,heatconductiontothedoughoccursonly through theband.Theband receives its energy store fromheat con-ductedthroughthesupportswhereitridesandfromconvectionandradiation.Dueto the localizednatureofconductive transfer, steep temperaturegradientscanbesetupwithinthedoughpiece,thehottestregionsbeingtheonescontactingwiththebandorpan.

Convectioninvolvesheattransferbyeitherfluidsorgasesinastateofmotion.Ahotbodygivesupsomeofitsheatandhenceincreasesthetemperatureofthegas-

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eousmediaaroundit.Ifthisheatedgaseousmediaflowsaroundacoldobject,heatwillbeabsorbedbythecoldobject.Thetopandsidesurfacesofanovenbecomehotandthusheatuptheovenatmosphere,whichinturngivesupsomeofitsheattoadoughpiece.Moleculesofairgases,watervapor,orcombustiongasescirculatethroughout theoven,constantlymixingwithothergasesand transferringheatbyconductionwhentheycontactwithsolidsurfacesintheovenchamber.Convectionoccursduetothemovementofwatervaporandothergaseswithinthedoughpiece.Inaddition,translocationofliquidwater,meltedshortening,andotherliquidscausesheattobetransferredfromoneregionofthedoughtoanother.Theconvectionmodeofheattransfercanbegeneralizedasasmoothingoreveningeffectonheatdistribu-tionwithinthedoughpiece.

Heattransferbyinfraredradiationisasignificantfactorinmostovens.Theseradiationsareconvertedintoheatthroughabsorptionbyandinteractionwithabsorb-ingmaterials;theyarenotinthemselvesheat.Theradiationmodeofheattransferhastwopropertiesmakingitsactiondifferentfromotherheattransfermodes:

It issubject toshadowingorblockingby interveningsubstances thatareopaquetoradiation.Itisveryresponsivetochangesinabsorptivecapacityofthedough.

Radiationenergycomesfromtheburnerflamesandallhotmetalpartsintheoven,anditisnotrequiredthattheovenpartberedhotorotherwisevisiblyheatedfortheradiationofinfraredrays.Thisradiantenergytravelsinastraightline,andmuchofitneverreachesthedoughpiecebecausesomesubstancesthatarenottrans-parenttotheradiationintercepttherays.Shadowingorblockingoutofradiationbysomeinterveningmaterialcanoccurfrompartsoftheoven,frompanwalls,orfrompartsofthedoughpieces.

Duringbaking,itcanbesaidthatconductionandradiationtendtocauselocal-izedtemperaturedifferentialsinawaythatconductionactstoraisethetemperatureofthebottomsandradiationactstoraisethetemperatureofexposedsurfaces,whileconvectiontendstoevenouttemperaturegradients.

... ChangesindoughduringBaking

Doughpiecesundergophysicalandchemicalchangeswithintheoven.Crustforma-tion,meltingofshorteninginthedough,conversionofwatertosteam,gasexpan-sion,andescapeofcarbondioxide,othergases,andsteamarethephysicalchangesoccurringbyheattreatment.

Theoutersurfaceofthedoughsoonbecomescoatedwithafilmorcrustonenter-ingtheoven.Crustthicknessdevelopsasmoistureisevaporatedfromtheoutsideskin.Crustformationstartsat26.7°Candproceedsquicklyataround37.8°C.Itisneces-sarythatthecrustachievesufficientthicknessinordertoallowittobecomeelastic.Themoisturecontentoftheproductandhumidityoftheovenatmosphereaffectthedegreeofelasticity,particularlyinthefirsttwozonesofafour-zoneoven.Thecrustfilmbecomestoothickiftheheatofthetopovenistoohighbecausethewatervaporandthegasesaresubsequentlyformedwithinthedough.Thistopcrusthavinglostits

•

•

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elasticitywillburstopen.Duetothis,insomecookietypes,collapseoftheinternalstructure isevident.Crustfilmelasticity isdirectlyrelated to theovenatmospherehumidity.Ifthefilmcrustisformedtoorapidly,theflowabilityofthedoughislim-ited;thereisasuppressionoftheleaveningactionandhencetextureformation.

Shorteningsdonothavesharpmeltingpointsastheyaremixturesofcompounds.Theaggregatesofshorteningparticlesmeltassoonastheirimmediateareainthedough reaches the melting, fusion, or slip-point temperature of shortening struc-ture.Althoughthelowermeltingpointfractionsseepintotheenvelopingstructure,shorteningpocketsremainmoreorlesswithintheiroriginalpositioninthedoughstructureandthuscontributetocookietexture.

Waterusedfordoughpreparationisconvertedtosteamduringheating.Steamformation makes the dough pieces expand. Expansion due to steam formation ismuchgreaterthantheexpansionduetocarbondioxideorammonia,despitecarbondioxidebeingevolvedmuchearlierintheoventhanthesteam.

Carbondioxideformationduetothechemicalreactionswithinthedoughpieceundertheeffectofincreasingtemperaturesincreasesthevolumeandstretchabilityofthedough.Themasswillbeopenedupbytheexpandinggasestohelptocreatethecrumbtexturedependingonthestrengthofthestructureofthegluten/starch/sugar/fatmatrix.

The overall dough volume is reduced as carbon dioxide and other gases andsteamareremoved.Ifthelossistoogreat,thiswillcausethestructuretocollapse,resultinginhollowedtopsandcrackedsurfaces.Notalloftheinternalgasesmustbeallowedtoescapeuntilthestructurebecomesmoreorlessset,otherwisethetexturethroughthefinalbakingstagesandthecoolingwillnotbemaintained.

Allofthephysicalchanges(especiallytheinternalones)mustbeencouragedtotakeplaceinanorder,environmentalconditions,temperature,andatimeoptimumfortheparticulardoughmakeupandthedesiredattributesofthecookietobeproduced.

Gasformation,proteinchanges,starchgelatinization,caramelizationofsugar,anddextrinizationarethechemicalchangestakingplaceintheoven.

Chemicalleaveningsystemsinvolveagassource,almostalwayssodiumbicar-bonate,andoneormoreacidreactingsubstances.Thefunctionofaleaveningacidistopromoteacontrolledandnearlycompleteevolutionofgasfromadoughwherecarbondioxideexitsinitsdissolvedform.Thereactionofacidandcarbonate(orcar-bonatealone)canbecontrolledbythesolubilityoftheparticularacidorcarbonateinthedoughmoisture,temperature,anddecompositionrangeofthecarbonate.

Gluten and other proteins derived from milk and eggs begin to coagulate attemperaturesfrom62.8°C.Thisproteincoagulationimpartsstrengthtothecookiestructure.Atarounda temperatureof73.9°C, theproteinsundergoan irreversibledenaturation—theybecomelesssolubleandtheproteinfibersbecomelessextensible.Hence,thevesiclewallsofthedoughstructureachieveamoreorlessfixedposition,wheretheexpansionofdoughpracticallystops.Thecoagulatedproteinisthedrierregioninthebakedcookie,thestarchholdsmostofthepresentmoisture,theshort-eninggivestenderness,andallcombinedgiveshortness.Themoistureinthecookiemigratesfromthestarchtotheproteingradually,evenwithoutlossofmoisturefromthebiscuittotheatmosphereduringtheshelflifeofthecookie.Thisisnotsoevidentincookieslikebread,wherethemoistureisgreaterwithrespecttocookies.

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Starch gelatinizes to form viscous solutions or rigid gels when heated in thepresenceofsufficientwater.Ifthegelatinizedstarchisallowedtocool,itbecomesmoreviscous.Whenstarchismixedwithcoldwater,itabsorbs30to35%ofwaterwithslightswellingofstarchgranules.Waterremovalleavesthestarchinitsorigi-nalstate.However,whenthestarch–watermixtureisheatedatatemperatureabove54.4°C, water absorption is greater, and the starch granules swell to many timestheiroriginalsize.Thestarchcannotberecoveredinitsoriginalstatebecausethisreactionisirreversible.Hence,starchgelatinizationprobablyplaysacrucialroleinproducingcookiestructureduringbaking.

Sugarcaramelizationtakesplacearound148.9°Caccompaniedbymelanoidins,andthisisthereasonforthedegreeofbrowncrustdevelopment.Caramelizationistheconsequenceofsugarmoleculessuchasmaltose,fructose,anddextrosetopro-ducethecoloredsubstancesclassifiedascaramels.Associatedwiththisreaction,theMaillardreactionduetotheinteractionofreducingsugarswithproteinsandothernitrogenoussubstancesgivesrisetoattractivecolors,flavors,andaromas.Atabout176.7°C,thebrowncolorseemsandtasteslikecaramel,andaround246.1to260°C,themelanoidinsbecomeblack,bitter,andinsoluble.

Starchisstartedtobeconvertedtodextrinattemperaturesslightlyhigherthan148.9°C.Ifaslightdegreeofdextrincanbeformedonthedoughsurfaceduringbak-ingunduecaramelization,thenasurfacebrightnessisdeveloped,whichisdesired.

... ovens

Direct-fired,indirect-fired,andhybridovensarethemaintypesofcookieoven-heat-ingsystems.

Indirect-gas-firedovens,many ribbonor stripburnersare locatedaboveandbelow thebakingband.Eachburner is suppliedwithcarburetedgasandair,andthepressureofthismixturedeterminesdeliveredpower.Inordertoprovideevenheatingacrosstheband,therearevariousarrangementsforadjustingtheflamesizeacrossthewidthoftheoven.Direct-gas-firedovensmayadditionallyhaveaturbu-lencesystemimprovingtheheattransferrate.Thetopofthebakingchamberisusu-allylow,andtheburnersareasneartothebandasispracticable,meaningthatthereisahighradiantheatcomponentintheheattransferprofilereachingtheproduct.

Electric-firedovensaresimilartodirect-gas-firedovens,buteachburnerissup-pliedwithelectricity.

Eachzoneoftheforcedconvectiondirect-firedovenshasonelargeburner,andthecombustionproductsareblowntoplenumchambersaboveandbelowtheband.Itispossibletocontrolblowingvelocityandtheratioofhotaircirculatedaboveandbelowtheband.Thebakingchamberroofofaforcedconvectiondirect-firedovenishigherthanthatofadirect-firedoveninordertomaintainevenairflows.Thismeansthatforcedconvectionovenscontributea lowerproportionofradiatedheat to theheattransferprofileyetallowmoreuniformtemperatureandheattransferconditionsacrossthebakingchamberwidth.

Inconvectoradiantovens,hotgasesfromtheburnerinazonepassthroughtubesaboveandbelowtheband,and then theyarereleasedfromfurther tubes toblowoverthefirsttubesinthebanddirection.Thefirsttubesradiateheattothecookies,

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andconvectioncurrentsofairaregivenbythereleasedair.Inordertomaximizetheradiantheateffect,theradianttubesarelocatedasnearasispracticabletothebakingband.

Indirectlyfiredforcedconvectionovensaresimilartothedirect-firedforcedcon-vectionovens,butaheatexchangernearthezoneburnerheatstheairpassingthroughplenumchambersinthebakingchamber.Hotgasespassthroughtubesaboveandbelow thebakingbandandcirculateback to theburner in indirectlyfiredCyclo-therm.Nocombustionproductspassintothebakingchamber,andthereisaseparateaircirculationsystemmovingairinthebakingchamberandoverthehottubes.

Hybridovensarethecombinationoftwoofthedirect-firedandindirectlyfiredovens.Averycommonhybridoveniscomposedofafirstzoneofdirectgasfiredfollowed by two or more zones of forced convection type. Maximum power andmuchradiantheatareavailableearlyinthebake,andthenmuchconvectedheatisprovidedforthedryingpartoftheoven.

Indirectlyfiredovensgenerallyhaveafewlargeburnerswiththeovendividedintolargezonesalongthelength.Direct-firedovenshavealargenumberofsmallburnersgroupedinsimilarlargezonesforcontrolpurposes.Indirect-firedovens,itispossibletoturnoffindividualburnerseitheraboveorbelowtheband.Dampersarepresenttocontrolanddivertthehotgases’passagetovariouspartsoftheovenchamberoruptothefluestotheatmosphere.Inadditiontothedirectandindirectoventypes,therearedesignspromotingconvectionorradiantheattransfer.Succes-sivezonesmighthaveadifferenteffectonheattransfertype,andahybridoventypemayhavedifferentfuelsindifferentzones.

The length of an oven and the baking time required to bake a cookie to thedesiredstructure,color,andmoisturecontentdefinetheproductionrateofanoven.Formostof theproducts, the timeneeded todry theproduct satisfactorilydeter-minesthebakingspeed.Itispossibletocalculatetheovenefficiencybymeasuringtheamountof fuelofknowncalorificvalueburned ina timecomparedwith theweightlossrepresentingthequantityofthewaterevaporatedandtemperatureriseofthecookieingredients.

Thereisaterminaldrumateachendoftheoven.Thedrumisdrivenattheovenexit,andthereisatensiondeviceholdingthebandtautatthefeedend.Thedrumshavesufficientdiameterinawaythatthebandsandtheirjointsarenotstrainedinflexing,andtheiraxlescanbeinclinedtofacilitatetracking.Itissometimesrequiredtocoatthedrumwithfibrousandfire-resistantmaterialtoeliminateslip.Thebandsaresupportedonmetalorgraphiterollersspacedcloselyenoughinordertopreventappreciablesaggingofthebandbetweenthemthroughtheoven.

Thedistancethattheovenbandextendsbeyondtheovenchamberateachendisrelatedtothewayaproductisplacedonitandalsotheamountofcoolingneededbeforethebakedproductcanberemoved.Wire-cutanddepositedcookiesneedlead-in space in order to allow room to locate the forming equipment over the band.Sugar-richcookiesneedlongrun-outlengths,possiblywithfan-assistedairorwaterspraycoolingundertheband,toallowthemtosethardpriortostrippingfromtheband.

Astrippingknife,whichmaybeathinbladeofsteelorahardsyntheticsub-stanceoracombofwirefingers,isusedtoremovethebakedcookiesfromtheband.

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Theknifeshouldbedesignedtoliftthecookieclearandtransferitwithminimumdisruption to the relative positioning of the cookies. This provides good feedingtothewrappingequipmentorforfurtherprocessing.Differenttypesofknivesareusedforliftingdifferenttypesofcookies.Itiscrucialthattheknifedoesnotbearsofirmlyonthebandthatitdamagesthesurfaceoftheband.

8.2.4 CoolinG

Thecookiesarecooledonaclothbandafter leaving theoven,and theyareveryhot,verysoft,andgenerallyverymoistastheyemergefromtheoven.Hence,eventhoughcooling isamust forpackaging, itmaybe the leastcrucialaspect, for somanyotherthingsaretakingplaceasthecookiecools.

Cookies having a crust temperature of 115.6°C and a crumb temperature ofabout99°Ccomingfromtheovenarestillinasomewhatplasticstate.Somewire-cutcookietypesaresosoftandmoltenthattheycannotbepickedoffthesteelbandneartheovenmouth.Inadditiontohightemperatureandmoisturecontent,thereareotherfactorstobeconsideredincookiecooling.However,twofactorsareeffectiveinhowtheotheringredientsreacttothecoolingcycle.Itseemsreasonabletosuggestthattheflourstarchisstillinsomegelatinouspasteform,anddextrinsarestillinpartialsolutionduetotherelativelyhighmoisturecontent.Sugarsareinatleastpar-tialsolutionaswell,andtheshorteningwillbepresentasoilratherthanasfat.Theproteinisprobablyinafirmerstatewithrespecttootheringredients.Thus,everyingredientisinanunsetstate,meaningthateachishot,moist,andsoft.

Ascoolingcontinues,withconsequentmoisturelossdueinparttotheusingupofsomeoftheinternalheatofthecookie,thechangeisfromageltoapasteandtoadrycomplexstructure.Thismayseemtodependonprotein,whichmayattractwaterfromthoseingredientssoreadytogiveitup,forexample,dextrinssettingtoabrittlecondition,sugarscrystallizingout,andatleastinwettedfilmsofstarchdryingout.Thus, thecookiebecomesrigid(i.e., set).Theshorteningdoesnotcrystallizeoutuntilthecookiereachesatemperaturewithinthesettingrangeofitsmakeupglycer-ides,anditmightevensolidifyinfractions.

Moistureloss, temperaturedecrease,andthechangesin thestateof themainingredientsaffectcookiedimensions,givingrisetoshrinkageandmaybecausingstresses to be set up within the cookie in reaching the set, nonmolten state. Thementionedstressesmaycausecrackingofthebiscuitstoagreateroralesserdegreeunderadverseconditions.Suddencoolingcanbeareasonforcracking,asitmightfirmupthecrustandretardthemoisturemigrationratefromthecentercrumbtotheedges.Thishappensduetotheexcessivemoisturegradientbetweentheseareas.

8.2.5 PaCkaGinGProCessandequiPmenT

Packagingandstoragearethelaststagesofcookieproduction.Thisstageisimportantintermsofitsprotectionpurpose.Thetimeperiodfromwhenthecookiesarepack-agedtoconsumptionisinfluencedbypackagingandstoragemethods,andtheflavor,taste,andappearanceofthecookiesshouldbeprotectedduringthistimeperiod.

Thepackagingmaterial shouldprotect thecookie fromharmfulenvironmen-taleffects.Theproductmustbeprotectedfromunduemoisturechangeduringits

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normal storage life as a primary requirement. When the packaging film protectsagainstmoisturetransferinanadequatemanner,itlikelyexcludesdirt,dust,moldspores,andotherforeignparticles,andinaddition,itgivessomeprotectionagainsttheabsorptionofoff-odors.

Asmostcookiesareverysusceptibletocrushing,mechanicalstrengthshouldbepresentinthecontainerifthecookieistosurvivestorageandtransportation.Thepackageshouldcontributetothedimensionalstabilityofthecookie.

Thepackagingmaterialofthecookiesshouldbeappropriateforbeingformedintothefinishedpackageeasilyandfastbymechanicalways.Afundamentalneedforpackagingfilmsisthatthestructureheat-sealreadily.Moreover,thepackagingmaterialshouldnottear,crack,orstretchduringtherapidtransfersandfoldingsinthewrappingequipment.

Thepackageshouldalsohelpsellthecookie.Transparentfilmsareusedwhenthevisibilityoftheproductisimportant.Aglossysurfaceenhancesconsumeraccep-tance,andprintabilityisneededinmostcases.

Inadditiontotheabovefactors,thepackagingfilmshouldberelativelylowinprice,andthesupplier’splantorwarehouseshouldbelocatedsoastomaketrans-portationcostsacceptable.

Packagingmaterialshavedifferentdegreesofresistancetowatervaportransferanddifferintheirbarrierpropertiestooxygenandothergases,hydrocarbons,andlight.Cellulosicmaterials,plasticresins,metalfilms,andlaminatesareusedgener-allyforpackagingmaterialsforcookies.Thecostofthepackagingmaterialchangesaccordingtothecontentofbasestockorresin,filmthickness,andcoatingapplica-tion.Theplasticfilmthicknessismoreorlessdirectlyrelatedtotherateatwhichwatervaporandoxygencandiffusethroughthefilm.

Toimprovethesealingcharacteristics,toestablishabettersubstrateforprintinginks,andtoimprovebarrierproperties,coatingscanbeapplied.

Withthemodificationofbasematerial,thickness,andcoatings,thebarrierprop-ertiesofpackagingmaterialscanbechangedtothedesireddirections.Laminationoftwoormorefilmsmayalsobeemployedinordertomodifybarrier,sealing,andvisualproperties.

Therearetwogeneraltypesofpackagingschemesemployedintheproductionofcookies:dumppackagingandregisteredpackaging.Indumppackaging,thesmallpiecesareallowedtofallintothepackinnoparticularorder.Inregisteredpackag-ing,thepiecesarekeptinsomepredeterminedrelationshiptoeachotherthroughoutthepackagingprocessandinthecontainer.

Fordumppackagingofsmall-tomedium-sizedcookies,verticalform-fillsealequipmentisusedwidely.Verticalform-fillsealpackagingequipmenttakesaflex-iblefilmstripandwrapsitaroundametaltubeopenatbothends.Twoverticaledgesoftheplasticstripsareoverlappedandheatsealed,andthismakesthewebintoaverticalcylinder.Acrossthementionedcylinderandjustbelowtheformingtube,aheatsealismadeassoonasaweighedamountofcookiesisdroppeddowntheform-ingtubeintotheclosed-offarea.Theclampdrawsthewebdownwardandpullsmoreofthefilmalongtheformingtube.Thesealingjawreturnstoitsoriginalpositionforanothersealingcyclewhenithasdrawndownapredeterminedlength.Next,it

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makesthetopsealofthebottombagandcutsitoffasitismakingthebottomsealofthenextbag.

Theform-fillsealercanbereplacedwithmanualfillingofpremadebagswhenthecookieproductionisinsmallscale.

Forregisteredpackagingofcookies(wherethecookiesarekeptinrelationshiptoeachotherduringpackagingandinthecontainer),thekindsofmachineryavail-able aremorevaried.Theprocess isoldbuthasbeen refined to thepointwherebreakageisminimalwithhighspeed.

Cartoningmachinesusedinthecookieproductioncanbegroupedaccordingtomodeofoperation(semiautomaticorfullyautomatic),thedirectionofloading(verticalorhorizontal),andmotiontype(continuousorintermittent).Semiautomaticequipment,whichrequiresthattheoperatorputthecookieinthecartonmanually,issaidtobemoresuitableifmanydifferentsizesareloadedandfrequentchangeoversareneeded.Thecookiesareloadedintocartonsautomaticallyinthefullyautomaticmode.

referenCes

Desrosier,N.W.1977. Elements of Food Technology.Westport,CT:AVI.Manley,D.J.R.2000.Technology of Biscuits, Crackers and Cookies, 3rded.BocaRaton,

FL:CRCPress.Pyler,E.J.1988.Baking Science and Technology,Vol.2.KansasCity,MO:Sosland.

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9 Heat and Mass Transfer during Baking of Sweet Goods

Weibiao Zhou, Nantawan Therdthai

Contents

9.1 Introduction................................................................................................. 1739.2 HeatTransferMechanismsduringBaking................................................. 174

9.2.1 ConductiveHeatTransfer................................................................ 1759.2.2 ConvectiveHeatTransfer................................................................. 1769.2.3 RadiativeHeatTransfer................................................................... 176

9.3 MassTransferMechanismsduringBaking................................................ 1789.3.1 MassDiffusion................................................................................. 1789.3.2 EvaporationontheSurfaceandMassConvection.......................... 1799.3.3 InternalEvaporationandCondensation........................................... 179

9.4 CombinedTransportPhenomenaduringBaking....................................... 1809.5 ImpactofHeatandMassTransferduringBakingonProduct

Characteristics............................................................................................. 1849.5.1 ImpactonVolumeExpansion.......................................................... 1849.5.2 ImpactonCrumbandCrustDevelopmentandBakingLoss.......... 1859.5.3 ImpactonCrustColor,Gloss,andFlavorDevelopment................. 186

9.6 ModelingandOptimizationofHeatandMassTransferBakingofSweetGoods................................................................................................ 1869.6.1 ModelingofHeatandMassTransferatProductLevel................... 1879.6.2 ModelingofHeatandMassTransferinOvenChamber................. 187

9.7 Conclusions................................................................................................. 188References.............................................................................................................. 188

. IntroduCtIon

Forsweetbakerygoods,bakingisakeyprocesstodevelopdesiredproductchar-acteristicsincludingstructure,texture,flavor,andcolor.Eachproducthasitsownrecipethatissupposedtoyieldthedistinctcharacteristicsoftheproduct.However,thosecharacteristicsareoftenthedirectconsequenceofheatandmasstransfersdur-ingbakinginanoven.

Typicalsweetgoodsincludingcakes,biscuits,crackers,pies,andsomebreadshavedifferentbakingprofiles.Ifthebakingtemperatureistoohighforaproduct,

52748.indb 173 2/6/08 2:26:39 PM



crustmaybeformedtooearly,resultinginamuchsmallervolume.Inaddition,thecrustmightbecometoodarkwhiletheinterioroftheproductisstillunderbaked.Incontrast,ifaproductisbakedunderalowtemperature,thebakingtimemayneedtobeextended todevelopadesiredbrowncrust color.However, a longerbakingtimecoulddevelopathickercrust.SomeEuropeanbreadvarietieshavethickcrustcharacteristics.Ingeneral,breadcanbebakedatatemperatureintherangeof200to240°C.Forcakes,a relatively lowerbaking temperature in therangeof175 to215°Cisgenerallyrequired.Ifthebakingtemperatureistoolow,bothmoisturelossandvolumecanbeincreased,whichresultsinweakcrumbanddrymouthfeel.Ontheotherhand,ifthebakingtemperatureistoohigh,thequalityofthecakemaybepoor.Notonlydoesthisresultinunderbakedcrumbandsmallvolume,butitalsocausespeakedtoporirregularcrumb(Conforti,2006).Inthecaseoffruitcakes,whenthebatterviscosityistoolow,fruitpieceshaveagreatertendencytosinktothebottomofthecakeduringbaking.Therefore,aslightlyhighertemperatureshouldbeusedtoshortenthetimeperiodoflowviscosity(CauvainandYoung,2001).Crack-ersrequireahigherbakingtemperatureintherangeof220to260°C.SlowbakingratescanproduceacoarsetextureinthecaseofGrahamcracker.Ontheotherhand,anoventemperaturethatistoohighmaycauseblistersincreamcrackers.Withaveryhightemperatureonthetop,abakedcreamcrackercanbedomed.Inaddition,withaveryhightemperatureatthebottom,dishingofabakedcreamcrackerispos-sible.Therefore,abalancebetweenthetopandbottomheatingplaysanimportantrole inproducingtherightcrackercharacteristics(YoneyaandNip,2006). In thecaseofpieswithfillings,alongbakingtimemightcauseaboil-outofthepiefill-ings.Toavoidboil-out,itisbettertobakethematahightemperatureforashorttime.Otherwise,thetotalsolublesolidinthepiefillingshastobeincreasedtoincreaseitsboilingpointaswellasdecreasetheequilibriumrelativehumidityofthefillings(CauvainandYoung,2001).

Itisclearthatallsweetgoodsrequireawell-designedandoftenuniquebakingcondition that could produce the correct product characteristics. However, fromanengineeringviewpoint,duringbaking,hightemperatureprofilesarecreatedindoughandbatter throughconvective,radiative,andconductiveheat transfers.Atthesametime,masstransfersincludingwaterdiffusion,evaporation,andconden-sationoccur.Thepropertiesofsweetgoodproductsincludingdensity,specificheat,and thermalconductivityhavebeenreviewedbyBaiketal. (2001).Thischapterfocuseson theheatandmass transfermechanismsduring thebakingprocessofsweetgoods.Their impactonphysicochemicalchangesof theproductswillalsobediscussed.

. heattransferMeChanIsMsdurIngBaKIng

Bakingisathermalprocessthatcarriesoutunderhightemperature.Generally,heatissuppliedtotheproductmainlyfromovenwallsthroughradiativeheat transfer.Inaddition,convectiveheatistransferredtotheproductfromhotairintheoven.Withintheproduct,conductiveheattransferisoftenthemainmechanism.

52748.indb 174 2/6/08 2:26:40 PM


Heat and Mass Transfer during Baking of Sweet Goods

9.2.1 ConduCTive heaTTransFer

Itiswellknownthatconductiveheatistransferredwithindoughand batter by direct contactbetween molecules without amacromovementof themateri-als.Temperaturegradient is thedriving force for heat transfer.As illustrated in Figure9.1, thedistance between two sides ofareaA(m2)inthedoughandbat-terisdenotedbydx(m),andthecorrespondingtemperaturechangeacrossthedistanceisdenotedbydT(°C).HeatflowratecanbedescribedusingFourier’slawasfollows:

q kA dT

dx=− ⋅ (9.1)

whereqisheatflowrate(W),dT/dxistemperaturegradient(K·m–1),andkisthermalconductivity(W∙m−1∙K−1).

Thermal conductivity is a physical property of dough and batter. It can varyconsiderably,dependingonproductcomposition.Thethermalconductivityofdoughandbattercanbeestimatedfromthequantityofconstituentsincludingwater,fat,protein,carbohydrate,andash.SinghandHeldman(2001)presentedanempiricalmodeldevelopedbySweat(1986)forpredictingthethermalconductivityofsolidandliquidfoodmaterialsasfollows:

k X X X X Xc p f a w= + + + +0 25 0 155 0 16 0 135 0 58. . . . . (9.2)

whereXwithsubscriptsofc,p,f,a,andwaremassfractionsofcarbohydrate,pro-tein,fat,ash,andwater,respectively.

Duringbaking,themoisturecontentofdoughandbatterchangesgraduallyandcontinuously;asaresult,itsthermalconductivitymaybedescribedasafunctionofmoisturecontent(Zanonietal.,1994):

k k

Wk W

Wd w= ⋅+

+ ⋅+

11 1

(9.3)

wherekd is thermalconductivityofdrymatter,whosevaluecanbetakenas0.40W∙m−1∙K−1;kw is thermalconductivityofwater,whosevaluecanbe takenas0.60W∙m−1∙K−1;andWismoisturecontentondrybasis(kgwater/kgdrymatter).

Rigorouslyspeaking,thethermalconductivityofvariousconstituentsofdoughand batter and therefore the thermal conductivity of dough and batter are also a

q

dx

A

fIgure. Conductiveheattransferwithinsweetgoodproducts.

52748.indb 175 2/6/08 2:26:42 PM



functionoftemperature.However,inpractice,constantvaluesarenormallyusedinsystemevaluations.

Table9.1listsvaluesofthethermalconductivityofsomesweetgoodsandbak-eryproductsthathavebeenreportedintheliterature.

9.2.2 ConveCTiveheaTTransFer

Convectiveheattransferinvolvesthemovementoffluidsincludingairintheovenandwaterinthedoughandbatter.Similartoheatconduction,differenceintempera-tureplaysakeyrole.Inabakingovenwithaconvectivefan,heatistransferredbyaforcedconvectionmechanismwhichisveryefficient.Theheattransferrateatthesurfaceofdoughandbatteraswellasatthesurfaceofvariousovenparts(duct,wall,andceiling)dependsonairflowvelocity.

Without a convective fan, heat is transferred fromair to a solid surfaceby anaturalconvectionmechanism,wherethetemperaturedifferencecreatesadensitygradientand thereby themovementofair.Assuch, thenaturalconvectionrate isdependentonthecoefficientofthermalexpansionofthefluid.

ConvectiveheattransfertakesplacewhenovenairattemperatureTismovingpastasurfaceattemperatureTs.Atthesurface,airvelocityispracticallyzero.Theareaadjacenttothesurfaceisathinlayerwheretheairvelocitycanbeverylowandisclassifiedasstreamline.Awayfromthesurface,velocityincreases,therebyheattransferrateincreases.FromNewton’slawofheating,heatflowperunitareaispro-portionaltothetemperaturedifferencebetweenthesurfaceandovenair,asfollows:

q hA T Ts= −( )

(9.4)

wherehistheheattransfercoefficient(W·m−2·K−1).Accordingtoastudyontheapparentheattransferinanoven(Satoetal.,1987),

heattransfercoefficientswerefoundtovarybetween9and20W·m−2·K−1whentheairvelocitywasintherangeof0.4to1.5m·s−1.WatsonandHarper(1988)statedthatheattransfercoefficientsofairundernaturalconvectionandforcedconvectionwereapproximately2.8to28W·m−2·K−1and11to110W·m−2·K−1,respectively.Forviscousfluids(e.g.,doughandbatter)underforcedconvection,heattransfercoefficientsareapproximately56to560W·m−2·K−1.

Heattransfercoefficientsmaybeestimatedusingdimensionalanalysis(SinghandHeldman,2001).Foranindustrialcontinuousbakingoven,Therdthaietal.(2003)estimatedtheheattransfercoefficientinsideheatingductstobeat100W·m−2·K−1,andtheoverallheattransfercoefficientforheatlossthroughtheovenwallsandceil-ingtobeapproximately0.3W·m−2·K−1.

9.2.3 radiaTiveheaTTransFer

Radiantheatistransferredtodoughandbatterasacombinationofabsorption,reflec-tion,andtransmission.Thefollowingequationholds:

α ρ τ+ + =re 1 (9.5)

whereαisabsorptivity,ρreisreflectivity,andτistransmissivity.

52748.indb 176 2/6/08 2:26:43 PM


Heat an

d M

ass Transfer d

urin

g Bakin

g of Sw

eet Go

od

s

taBle.

thermalConductivityofsweetgoodsandBakeryProductsProduct temperature(°C) MoistureContent(%wetbasis) thermalConductivity(W·m–·K–) ref.

Breaddough -22.0 43.5 0.880 Lind(1988)

23.025.0

43.540.0

0.4600.290

Lind(1988);Sumnuetal.(2007)

Bread 25.090.0

40.033.0

0.0700.110

ThorvaldssonandJanestad(1999);Sumnuetal.(2007)

Frenchbread Roomtemperature 42.0 0.0989 Sweat(1985)

Whitebread 25 — 0.158±0.012 Touetal.(1995)

60–70 — 0.304±0.040 Touetal.(1995)

80–90 — 0.353±0.075 Touetal.(1995)

Biscuitdough 29.8 4.1 0.405±0.22 KulachiandKennedy(1978)

Biscuit — — 0.07–0.16 Standing(1974)

Yellowcakebatter — 41.5 0.223 Sweat(1973)

Yellowcake — 35.5 0.121 Sweat(1973)

Cupcakebatter 20±1.2 34.6±1.93 0.206±0.007 Baiketal.(1999)

Cupcake(19.5minbakingtime) 20±1.2 27.6±2.06 0.0683±0.004 Baiketal.(1999)

Muffin — 17 0.70 TouandTadano(1991)

Tortilladough 55–75 50–60 0.0366–0.1079 Griffith(1985)

Tortilla — — 0.25±0.020 Alvaro-Giletal.(1995)

Tandooriroti — — 0.128 Saxenaetal.(1995)

Chapati 58.5 43.0 0.330 Gupta(2001)

Source:ExceptthosedatafromThorvaldsson,K.andJanestad,H.,Journal of Food Engineering,40,167–172,1999;Gupta,T.R.,Journal of Food Engineering,47,313–319,2001;andSumnu,G.,Datta,A.K.,Sahin,S.,Keskin,S.O.,andRakesh,V.,Journal of Food Engineering,78,1382–1387,2007,allotherdataareadaptedfromBaik,O.D.,Marcotte,M.,Sablani,S.S.,andCastaigne,F.,Critical Reviews in Food Science and Nutrition,41,321–352,2001.

52748.indb 1772/6/08 2:26:44 P

M



Forblackbodies, the absorptivity ismaximized (i.e.,α = 1). However, doughorbatterisnotablackbody.Emissivityofthesurfaceofdoughorbatter,whichisdefinedastheratiooftheemissivepowerofthesurfacetotheemissivepoweroftheblackbody,isassumedtobearound0.90(DeVriesetal.,1995;ThorvaldssonandJanestad,1999)or0.95(Zanonietal.,1994).Theradiantheattodoughandbattercanbeestimatedasfollows:

q A T T= −( )ε σ 1

424 (9.6)

where ε is emissivity and σ is the Stefan–Boltzmann constant (5.6697 × 10−8W·m−2·K−4).

. MasstransferMeChanIsMsdurIngBaKIng

Duringbaking,water indoughandbatter is transferred throughporeswithin thedoughandbattertothesurfaceandfurthertotheairoutsidethedoughandbatter.Thiscausesastructuretransformationfromdoughandbattertocrumbandcrust,aswellasamoistureloss.Themoisturelossduringbakingisthehighestcomparedto those inotherprocessingstepsofsweetgoods.Themass transfermechanismsinvolvedinthestructuretransformationandmoisturelossincludemassdiffusion,evaporation, condensation, andmass convection.Thesemechanisms also interactwiththeheattransfermodes.

9.3.1 massdiFFusion

ByFick’slaw,massdiffusionisdrivenbytheconcentrationdifferenceasfollows:

mA

D dCdx

=− ⋅

(9.7)

wheremisdiffusionrate(kg.s−1),Aisarea(m2),Cisconcentration(kg.m−3),andDisdiffusivity(m2.s−1).Diffusivityisaphysicalpropertydependingontemperature,pressure,andsystemcomposition.

ThorvaldssonandJanestad(1999)proposedthefollowingmodeltoestimatethediffusivityofwatervapor(Dv)indoughasafunctionoftemperature(T):

D Tv = × ⋅−9 0 10 12 2. (9.8)

Typically,thediffusivitiesofliquidwaterandwatervaporareapproximately1.35×10−10m2.s−1and8×10−7m2.s−1at25°C,respectively.

Tocountfor theeffectofmoisturecontent,Zanonietal. (1994)proposedthefollowingmodeltoestimatevariationsinthediffusivityofliquidwater.Whenthemoisturecontentisbelow0.43,

D W D

w = ⋅ 0

0 43. (9.9)

52748.indb 178 2/6/08 2:26:46 PM



whereWisthemassfractionofunboundwater(kgwater/kgdrymatter),Dwisdif-fusivity,andD0isthediffusivitywhenthemassfractionofunboundwaterismorethan0.43anditsvalueisapproximately1.0×10−9m2.s−1.

9.3.2 evaPoraTiononThesurFaCeandmassConveCTion

Duringtheearlystageofbaking,waterisvaporizedfromthesurfaceofdoughandbatter toairusinglatentheatofevaporation.Whenthemassfractionofunboundwater ismore than0.43, latentheatofevaporation(∆H0) isapproximately2.3339MJ.kg−1.However,duringbaking,unboundwaterisgraduallydecreased.Whenthemassfractionofunboundwater(W)isreducedtolessthan0.43,thelatentheat(∆H)canbeestimatedfromthefollowingequation:

∆ ∆H L

WH= +

100 0 (9.10)

whereLis2.4948MJ.kg−1(Zanonietal.,1994).Duringbaking,thereexistsaconcentrationgradientofwatervaporbetweenthe

productsurfaceandair.Therefore,watervaporistransferredthroughmassconvec-tion.Itcanbedescribedby

mA

k C Cm s b= ⋅ −( ) (9.11)

wherekmisthemasstransfercoefficient(m.s−1),Csiswatervaporconcentrationontheproductsurface(kg.m−3),andCbiswatervaporconcentrationinbulkair(kg.m−3).

Similartoheattransfercoefficients,masstransfercoefficientsmayalsobeesti-matedthroughdimensionalanalysis(SinghandHeldman,2001).

9.3.3 inTernalevaPoraTionandCondensaTion

Duringbaking,temperatureinouterlayersofdoughandbatterincreasesfirst.Asaresult,thepartialwatervaporpressureinporesinthoselayersincreases.Duetovaporpressuredifference,watervapormoves toward the center throughpores ininnerlayers.Intheinnerlayerswheretemperatureislow,thewatervaporbecomescondensed.Therefore,theliquidwatercontentintheinnerlayersisincreased,andaliquidwatergradientisbuiltup.Theliquidwaterstartsmovingtowardthesurface,butitismuchslowerthanthewatervapormovementtowardthecenter(Thorvalds-sonandJanestad,1999).Thus, themoisturecontentof thecrumbat thecenter ishigherthanthemoisturecontentofdough.DeVriesetal.(1989)foundanincreaseofwatercontentby3.5gwater/100gbreadintheloafcenterimmediatelyafterbaking,buteventuallythewatercontentintheloafcenterwasdecreasedtothesamelevelasthatindough.Inthecaseofbiscuitswheresurfacelayersdryoutquicklyandthere-foretheevaporationfrontmovesveryfasttowardthecenter,innerlayersareheatedupquickly.Condensationinthecentralareamightnotbesignificant.However,boil-ing(evaporation)anddryingcouldbecomedominating.Furthermore,condensation

52748.indb 179 2/6/08 2:26:47 PM



mightbefoundonthesurfaceatthebeginningofbakingwhensteamisintroducedintotheovenanddoughsurfacetemperatureisstilllow(Savoyeetal.,1992).

. CoMBInedtransPortPhenoMenadurIngBaKIng

Duringbaking, transportphenomenacanbegroupedbasedon two levels:withinthebakingovenandwithintheproduct.Forexample,inanindirect-heatingbakingoven,heatissuppliedbyhotairthroughducts.Aftertheductsurfaceisheatedup,itgeneratesradiantheattodough.Inaddition,naturalconvectiveheattransfertakesplacefromairintheovenchambertothedoughsurface,whileforcedconvectiveheattransfercanoccurusingconvectivefans.Inadditiontothehotductsurfaces,allmetalsurfacesincludingovenwallsandceilingcangenerateradiantheat.Notonlyheatsupplyshouldbeaccountedfor,butheatlossalsoremainsasatopconcern.Althoughbakingovenshavebeenbuiltwithgoodinsulation,anappreciableamountofheatlossthroughthewallsisstillobservedformostoftheovens,mainlybynatu-ralconvectiveheattransfer.

Foran industrial traveling-traybakingoven,Therdthaietal. (2004a)summa-rizedthevariousstatesofheattransferasfollows:

Convectiveheattransferfromhotductsurfacestoairintheovenchambercanbecalculatedby

qa=haA(Tduct–Tairinsideoven) (9.12)

withitsinitialconditionasTair inside oven = Ta0att = 0,where Ta0istheinitialovenairtemperature.Heattransfercoefficienthacanbecalculatedthroughdimensionalanalysisaccordingtotheflowstatusinsidetheovenchamber.Atthesametime,radiantheatcamefromallhotmetalpartsintheoven,traveledstraightthroughthespace,andcausedlocalizedtemperaturedif-ferentials.Thisradiantheatwascalculatedby

qb=σεA[(TA+273)4–(TB+273)4] (9.13)

whereTA isthetemperatureoftheheatsource(°C)andTB isthetempera-tureoftheheatsink(°C).ThecorrespondinginitialconditionwasTB = TB0=40°C att = 0.Heatlossthroughtheovenwallswhichwereinsulatedwithfiberglasscouldbeverysmall.Itwascalculatedby

qc=hcA(Toveninnerwall–Tairoutsideoven) (9.14)

withitsinitialconditionasToven inner wall = Tc0att = 0,whereTc0istheinitialinner wall temperature of the oven. The overall heat transfer coefficienthc from thecombinedconductionandconvectionwasapproximately0.3W·m−2·°C−1.

•

•

•

52748.indb 180 2/6/08 2:26:47 PM



Theabovesetofequationswassolvedbyusingcomputationalfluiddynamics(CFD)techniquesforthewholeovenduringtheentirebakingperiod.

Forbiscuitsbakedinanaturalgasindirect-firedpilotoven,Fahlouletal.(1995)describedtheheatbalanceontheproductasfollows:

ev C T

xq q q q

Apcd cv r evaporationρ

∂∂=

+ + −( ) (9.15)

whereeisproductthickness(m);visconveyorspeed(m·s−1);δisdensity(kg·m−3);Cpisspecificheat(J·kg−1·K−1);qcd,qcv,andqrareheattransferratesbyconduction,convection,andradiation,respectively;andqevaporationistheenergyraterequiredforevaporation.

Cpwasestimatedbythefollowingmodel(Baiketal.,2001):

C WC W Cp p water p drysolid= + −( )( ) ( )1 (9.16)

where W is the mass fraction of water (kg water/kg dry matter). During baking,temperaturechangescontinuouslyandtherebyaffectsthevalueofspecificheat.Thefollowingequationscanbeusedforestimation(Fahlouletal.,1994):

C Tp drysolid( ) = +5 25 (9.17)

C Tp water( ) . . .= ⋅ − × ⋅ + ×− −1000 5 207 73 17 10 1 35 104 5 ⋅⋅( )T 2 (9.18)

Massbalancecouldbeexpressedasfollows(Fahlouletal.,1994):

m dX

dxmb

bevaporation⋅ =− (9.19)

wherembistherateofbiscuitthroughput(kg.s−1),Xbismoisturecontentofthebis-cuit(%),andmevaporationistherateofwaterevaporated(kg.s−1).

Zanonietal.(1994)attemptedtodescribevarioustemperatureprofileswithinacylindricalbreadloafatdifferentstatesofbaking.Thedoughorbreadwasplacedinacylindricalmoldandstoodononeend.Attheuppersurfacethatwasexposeddirectlytoair,temperaturegradientwasaresultofconvectionbetweenairandthedoughsurfaceandconductiveheattransfertowardtheinsideofthedough.More-over, therewasa convectivewatervapor transferbetween thedough surfaceandair.Thus,afterdiscretizingthesolutionspaceintogrids,temperaturechangeattheuppersurfacecouldbedescribedbythefollowingequation:

52748.indb 181 2/6/08 2:26:50 PM



dTdt

h T T I Jx

kd Tdx

kd Tdr

kdTds

a s

=

−( )+ + +

( ( , )∆

2

2

2

2 rr rC

kC x

P T

p

m

ps

1

ρ

ρ

−

∆,WW P T W H T Wa[ ]− [ ]( ), [ , ]∆

(9.20)

whereI,Jaregridcoordinators;Tistemperature(K);tistime(s);xisheight(m);risradius(m);hisheattransfercoefficient(W·m−2·K−1);kisthermalconductivity(W∙m−1∙K−1);∆x is infinitesimalheight interval (m);km ismass transfercoefficient(kg.s−1.m−2.Pa−1);ρ is density (kg·m−3); Cp is specific heat (J·kg−1·K−1); P is vaporpressure(Pa);Psisthevaporpressureatthesurface;Paisthevaporpressureinthesurroundingair;Taistheairtemperature;andT sisthesurfacetemperature.

Oncethesurfacetemperaturereached100°C,iftherewasenoughliquidwateronthesurface,evaporationwouldtakeplaceataconstanttemperatureof100°C.Mean-while,thesurfacetemperaturewouldalsoremainatthisconstanttemperature.

Duetoevaporation,themoisturecontentatthesurfacecontinuouslydecreased.Crustwassubsequentlyformed,andthesurfacetemperaturewouldincreasetowardthe oven temperature. At this stage, the temperature profile at the upper surfacecouldbeexpressedasfollows:

dTdt

h T T I Jx

kd Tdx

kd Tdr

kdTds

a s

=

−( )+ + +

( ( , )∆

2

2

2

2 rr rC p

1

ρ

(9.21)

whereI,Jaregridcoordinators;Tistemperature(K); tistime(s);xisheight(m);risradius(m);hisheattransfercoefficient(W·m−2·K−1);kisthermalconductivity(W∙m−1∙K−1);∆xisinfinitesimalheightinterval(m);ρisdensity(kg·m−3);Cpisspe-cificheat(J·kg−1·K−1);Taistheairtemperature;andT sisthesurfacetemperature.

Meanwhile,theinteriorofthedoughwasheatedbyconductiveheattransferinaccordancewithFourier’slaw:

dTdt

kC

d Tdx

d Tdr

dTdr rp

= + +

ρ

2

2

2

2

1 (9.22)

whereTistemperature(K), tistime(s),xisheight(m),risradius(m),kisthermalconductivity(W∙m−1∙K−1),ρisdensity(kg·m−3),andCpisspecificheat(J·kg−1·K−1).

Similarly to thedough surface,when temperature at an innerdoughpositionreached100°C,evaporationwouldtakeplaceatconstanttemperature.Therefore,thetemperatureatthatinnerpositionwouldnotchangeanymoreuntilthemoistureatthepositiontotallydriedout.

52748.indb 182 2/6/08 2:26:52 PM



Regarding moisture change during baking, Zanoni et al. (1994) described itaccordingtotemperatureprofilesasfollows.

Atthebeginning,masstransferattheuppersurfaceofthedoughincludedacon-vectivemasstransferbetweenairandthedoughsurfaceandamassdiffusionfromtheinnerlayerstowardthesurface.Themoistureprofilecouldbedescribedby

dWdt

Dd Wdx

Dd Wdr

DdWdr r

s = + + −2

2

2

2

1 kx

P T W P T Wms aρ∆

, ,

−

( ) (9.23)

where Wisabsolutemoisture(kgwater/kgdrymatter),Wsistheabsolutemoistureatthesurface,tistime(s),xisheight(m),risradius(m),Disdiffusivity(m2·s−1),∆xisinfinitesimalheightinterval(m),kmismasstransfercoefficient(kg.s−1·m−2·Pa−1),ρisdensity(kg·m−3),Pisvaporpressure(Pa),Psisthevaporpressureatthesurface,andPaisthevaporpressureinthesurroundingair.

Whensurface temperature reached100°C,evaporation tookplaceatconstanttemperature.Themoisturecontentcouldthenbedescribedby

dWdt

Dd Wdx

Dd Wdr

DdWdr r

h T T I J

s

a s

= + + −

−(2

2

2

2

1( ( , )))

+ + +

∆

∆x

kd Tdx

kd Tdr

kTdr r

H T W

2

2

2

2

1

ρ ,

(9.24)

where Wisabsolutemoisture(kgwater/kgdrymatter),Wsistheabsolutemoistureatthesurface,Tistemperature(K),tistime(s),xisheight(m),risradius(m),Disdiffusivity(m2·s−1), hisheattransfercoefficient(W·m−2·K−1),kisthermalconductivity(W∙m−1∙K−1),∆xisinfinitesimalheightinterval(m),δisdensity(kg·m−3),∆Hislatentheatofevapora-tion(J.kg−1),Taistheairtemperature,andT sisthesurfacetemperature.

Whentheevaporationfrontmovedtowardtheinside(i.e.,adriedsurface),thesurfacetemperatureincreasedtowardtheoventemperature.Atthisstage,themois-turecontentatthesurfacecouldbedescribedby

dWdt

Dd Wdx

Dd Wdr

DdWdr r

s = + +2

2

2

2

1 (9.25)

where Wisabsolutemoisture(kgwater/kgdrymatter), Wsistheabsolutemoistureatthesurface,tistime(s),xisheight(m),risradius(m),andDisdiffusivity(m2.s−1).

Fortheinteriorofthedough,moisturecontentwasnormallydeterminedaccord-ingtoFick’slaw:

dWdt

Dd Wdx

Dd Wdr

DdWdr r

= + +2

2

2

2

1 (9.26)

52748.indb 183 2/6/08 2:26:55 PM



However,whentemperatureataninnerdoughpositionreached100°Csothatevaporation at constant temperature happened, moisture content at that positioncouldbedescribedby

dWdt

Dd Wdx

Dd Wdr

DdWdr r

k= + +

−

2

2

2

2

1ρ∆∆H T W

d Tdx

d Tdr

dTdr r,

+ +

2

2

2

2

1 (9.27)

where Wisabsolutemoisture(kgwater/kgdrymatter),tistime(s),xisheight(m),risradius(m),Disdiffusivity(m2.s−1),kisthermalconductivity(W∙m−1∙K−1),ρisdensity(kg·m−3),∆Hislatentheatofevaporation(J.kg−1),andTistemperature(K).

It is worth noting that the internal evaporation and condensation mechanismdescribedinSection9.3.3wasnotconsideredintheaboveequations.

. IMPaCtofheatandMasstransferdurIng BaKIngonProduCtCharaCterIstICs

Amongthewholeproductionprocedureofsweetgoods,bakingisthekeystepthatdevelopstheproductcharacteristics,includingcolor,texture,andflavor.Forbread,bakingisaprocesstotransformdoughintocrumbandcruststructures.Forcakes,bakingisaprocesstotransformbatterwhichcontainsafoamstructureintoaspongestructure(CauvainandYoung,2001).Thedevelopmentinvolvesseveralmechanismsincludingnonenzymaticbrowningreactions,starchgelatinization,andproteindena-turation. Previous studies have focused on nonenzymatic browning reactions todevelopcolorandflavor,aswellasstarchgelatinizationandproteindenaturationtodevelopstructureandtexture.

9.5.1 imPaCTonvolumeexPansion

Duringbreadbaking,volumeexpansion ismainlydue to twomechanisms:yeastand water vapor. At temperatures below 55°C, yeast converts sugar into carbondioxide and thereby volume expands. Due to heat transfer, dough temperature isincreased.Attemperaturesabove55°C,yeastisinactivated.However,doughvolumestillincreasesbecauseofincreasedwatervaporpressure.Fordoughthatisheatedquicklyatthebeginningofbaking,itsvolumeexpansioncanbestoppedatanearlystage.Indeed,ifcrustisformedtooearly,itwillblockmasstransferfrominsidelay-erstoouterlayers.Theresultantvolumecanbesmallerthanthatdesired.Inaddition,crustformationseemstoplayanimportantroleintheformationofcrumbstructureintermsofporosity.Witharestrictedtotalvolumeconfinedbythecrust,doughmaycontinuouslyexpandlocallytothedetrimentofmechanicallyweakareas;asaresult,theporosityinthoseareaswasdecreased(Zhangetal.,2007).Therefore,therateofheattransfertodoughatanearlybakingstageshouldbeofgreatconcerninregardtovolumeexpansion.However,itisworthmentioningthatvolumeexpansionduringbakingisgenerallysmallerthanthatduringproofing.

Incakebaking,batterisconvertedtoaproductwithdesiredeatingcharacteris-tics.Forcakescontainingraisingagents,whenbatterenterstheovenandisheated,

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aircellsinthebatterbegintoexpandascarbondioxideisreleasedtoinflatethecells.Thisphenomenonhappensatfirstintheouterlayersandextendstotheinnerbatter.Therisingofvolumecontinuesuntilthestructureissetbystarchgelatinization.Cellexpansionandstarchgelatinizationtransformthebatterintocakecrumbstructurecontaininginterconnectedcells.Fortheskin,itsformationrateisdependentonbak-ingtemperature.Theskinofcakecanbequicklyformedinthepresenceofahighbakingtemperature.However,theearlyformedcrustisnotstrongenoughtopreventvolumeexpansioninthecaseofcakes,particularlywhenalargeamountofbakingpowderisused(CauvainandYoung,2000).

9.5.2 imPaCTonCrumBandCrusTdeveloPmenTandBakinGloss

Duetoheatandmasstransferatthedoughsurface,surfacemoisturecontentcouldbesignificantlyreduced.Asaresult,arelativelyhardlayerisformedwhichbecomescrustorskin.Generally30minbakingofasmallloafmaycreatea3mmthicknessofcrust.Ifincreasingthebakingtimeto50minforabigloaf,crustthicknessmayincreaseto5mm.Thecrustformationrateseemstobelinearwithrespecttotime(Wiggins, 1999). When a lower temperature is applied, a longer baking time isrequired,whichcausesformationofathickercrust.

Aftercrustisformed,heatisstilltransferredtothedoughwhichcanincreasetheevaporationrate.However,moisturefrominnerlayersishardlyremoved.Thisisduetothefactthatthecrustactsasabarriertoblockmasstransferfrominnerlayerstoouterlayers.Therefore,condensationatthecenteroftheloafisobserved,andmois-turecontentintheinnerlayersismuchhigherthanthatinthecrust.Accordingtoastudyonwaterdiffusioninbreadduringbaking(ThorvaldssonandSkjoldebrand,1998),themoisturecontentofcrustwasfoundtobe0±2.1gwater/100gdough,whereasthemoisturecontentofcentercrumbwas49.6±5.4gwater/100gdough.Moisturelossduringbreadbakingwasmainlyfromthecrustpartincludingtopcrust,sidecrust,andbottomcrust,as shown inFigure9.2.Fora typical bread loaf of 800g,weightlossduringbakingwasfoundtobeintherangeof50to55g.Forsometypesofbreadwhichhavethickercrust, higher weight losscan be expected (Wiggins,1999).

In addition to bakingtime,increasingbakingtem-perature tends to increasethe rate of moisture loss incakes (Cauvain and Young,2001). Similarly, Fahloul etal.(1994)demonstratedthatthemoisturecontent inbis-

3 mm

18.7 g of water loss

10.4 g of water loss

3 mm

5 mm

29 g of water loss

fIgure. Moisturelossduringbaking.(DatafromThorvaldsson, K. and Skjoldebrand, C., Lebensmittel Wissenschaft und Technologie,31,658–663,1998.

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cuitsdecreasedfrom0.24g/gdrymatterto0.10,0.05,andnearly0g/gdrymatterafterbakingat150°C,200°C,and250°C,respectively,for6to8min.

9.5.3 imPaCTonCrusTColor,Gloss,andFlavordeveloPmenT

Crust color was developed through nonenzymatic reactions including Maillardreactionsandcaramelization.Bothmechanismsareinvolvedinthermalprocesses.Maillardreactionswerebetweenaminoacidsandreducingsugarsunderasuitabletemperaturethatnormallyneedstobeabove50°C(Villamiel,2006).Itcanbestimu-latedwhenmoistureisdecreased.Thatmeanscrustcolorcanbeobservedassoonasevaporationatthedoughsurfaceiscompletedandthesurfacetemperatureincreasestowardtheovenairtemperature.Whenbakingtimeislonger,themoisturecontentatthesurfaceisgettinglower,andthesurfacetemperatureisgettinghigher.Thus,crustcolorintensitycanbeincreased.However,theincreaseindegreeofbrowningisnotlinearwithrespecttoincreaseintemperatureduetoradiantheatfrommetalwallsintheoven.Whendoughgetsbrowner,itsemissivitybecomeshigher.Sub-sequently,thesurfacetemperatureisincreasedmorequickly.NotonlydoeshighersurfacetemperaturestimulateMaillardreactions,butitalsocausescaramelization.Therefore, at the late baking stage, color development rate is enhanced. There isalsoasimilarproblemastovolumeexpansionwhenarapidheatingrateisappliedatthebeginningofbaking.Arapidheatingtodoughcanincreasethemasstransferrateandtherebymoistureloss.Asaresult,Maillardreactionsstartearly,whichmayyieldthecolorofbakedgoodsbeingtoodark.

Forcakes,usingalowerbakingtemperaturemightcausealongersettingtime,and accordingly, the texturebecomesdry.Dryingout can concentrate sucrose intheunsetportionofacake,resultingincaramelization.Asaresult,coloredcrustbecomesthicker.Inaddition,theinnercrumblayerthatisnotincontactwiththeovensteambecomesdryanddiscolored(CauvainandYoung,2000).

Todevelopaglosscrust,steamisrequiredduringthefirstfewsecondsofthebakingprocess.Glossdevelopmentneedsvaporcondensationonthecrustsurfacetoformastarchpaste.Withaminimumoventemperatureof74°Cforsufficienttime(optionalconditionisat77°Cfor10minor99°Cfor15sec),thestarchpastecangelatinize,formdextrin,andstartcaramelization(Wiggins,1999).Therefore,bothcolorandglosscanbefoundonthesurface.

Flavor in the formofn-heterocycles isdeveloped throughMaillard reactions.Majorcompoundsfoundinwheatcrustare2-acetyl-1-pyrolineand2-acetyltetrahy-dropyridine.Flavorcompoundsareabsorbedintotheporestructureofcrumbandareblockedfromdispersingtoairbycrust(ZhouandTherdthai,2007).

. ModelIngandoPtIMIzatIonofheatand MasstransferBaKIngofsWeetgoods

Baking is a complex process that transformsdough or batter into rigidproducts.Many studies have been conducted to develop mathematical models in order tosimulateandbetterunderstandthevariousphenomenaduringbaking.Thestudiedphenomenaduringbakingcouldbebroadlydividedintotwocategories:insidethe

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product(micro)andinsidetheoven(macro).Thissectionreviewsthepreviousstud-iesinvolvingbakingmodels.

9.6.1 modelinGoFheaTandmassTransFeraTProduCTlevel

Heatandmasstransferwithinbakeryproductshavebeenmodeledmainlytoexplaincrustandcrumbdevelopment.Theprogressofcrustlayertowardtheinnerregioncouldbesuccessfullysimulated.Whenheatisappliedtodough,wateratthewarmersideofagrain(pore)thatabsorbslatentheatofvaporizationcouldbeevaporated.Somevapormigratestoacoolerareawithintheloafandbecomescondensate,whilesomevaporescapestotheovenchamber(DeVriesetal.,1989).Zanonietal.(1993)set100°Castheevaporationfront temperature.Asaresult,unboundwaterat thesurfacewouldbeevaporatedthroughwaterboilingphenomenon.Thismechanismcouldbeaccelerated,whenwatervaporpressureintheovenairisfarfromsaturation(EliassonandLarsson,1993).Thencrust,whichisadriedlayer,willbeformedandseparatedfromcrumbthatismoist.

Mathematical models could also be established to simulate temperature andmoisturechangesduringbaking,suchasthosedescribedinSection9.4.Formasstransfer, mathematical models have been established to simulate water migrationwithin the dough (Thorvaldsson and Janestad, 1999; Thorvaldsson and Skjolde-brand,1998;TongandLund,1993;Zanonietal.,1994;Zhou,2005).Itwasfoundthatmoisturelosswasmainlyfromthetopsurfacewhichisexposeddirectlytoovenair.Moisture loss through thesidewassimilar to that through thebottom(Thor-valdssonandSkjoldebrand,1998).

9.6.2 modelinGoFheaTandmassTransFerinovenChamBer

Withinabakingovenchamber,fluidsincludinggasandwatervaporcirculateandtransfer heat to dough and batter. However, different oven designs have differentdominating heat transfer modes and patterns. Typical baking ovens significantlyrelyonradiationheattransferfromallmetalpiecesinthechamber(Velthuisetal.,1993).InovensforIndianflatbread,conductionseemstobethemostimportantheattransfermode(Gupta,2001).Mathematicalmodelsatthechamberlevelhavebeenestablishedforbatchovens(TongandLund,1993)andcontinuousovens(Fahlouletal.,1995;Gupta,2001;Savoyeetal.,1992).Duetothecomplexityofbakingovens,CFD has been used to simulate flow phenomena during baking (De Vries et al.,1995;Therdthaietal.,2003,2004a;Wongetal.,2007a).InadditiontoCFDmodels,neuralnetworkmodels,whichareblackboxmodels,couldalsobeused(KimandCho,1997).

Toobtainahigh-qualitybakeryproduct,optimizationofheatandmasstransferisnecessary.Theimpactsofprocessparametersonqualityattributeshavebeenstud-iedandmodeled,includingcrustcolordevelopment(TanandZhou,2003;Zanonietal.,1995a;ZhouandTan,2005),starchgelatinization(Therdthaietal.,2004b;Zanonietal.,1995b),crustthickness(Zanonietal.,1994),volumeexpansion(Fanet al., 1999), and moisture loss (Thorvaldsson and Janestad, 1999; ThorvaldssonandSkjoldebrand,1998).Usingmathematicaltools,optimizingtemperatureprofilesanddesigning thecorrespondingoptimumoperatingconditioncouldbeachieved

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(Therdthai et al., 2002, 2004a). To maintain the oven operating condition at theoptimumlevel,agoodprocesscontrolsystemshouldbeinplacetoensurethecon-sistencyofproductquality(Trystram,1997;Wongetal.,2007b).

. ConClusIons

Duringbaking,heatandmasstransferplaythemostimportantroleindevelopingphysicalandchemicalchangesinthebakeryproducts.Doughistransformedtoaproductconsistingofcrumbandcrustorskin,duetoheatandmasstransferwithindoughaswellaswithintheovenchamber.

Designofdifferentbakingovensprovidesvariouscombinationsofheattransfermodes, includingconvection, radiation,andconduction,and therebyvarious tem-peratureprofilesintheproductduringbaking.Theinteractionbetweenrateofmasstransferandrateofheattransferdependsonmanyfactorsincludingmodeofheattransfer,typeofproduct,andtypeofoven.Duetovariationintemperatureprofilesandmasstransferrates,theobtainedbakedproductsexhibitdifferentcharacteristicsincludingcrustcolor,crustthickness,volume,structure,texture,andflavor,resultinginvarietiesofsweetgoods.

Themodelingofheatandmasstransferwithindoughandovenchamberhasbeenstudied by many researchers where various phenomena during baking have beensimulated.Withtheknowledgeoftheimpactofheatandmasstransferonthecharac-teristicsofproducts,mathematicalmodelshavebeenusedforoptimizingovenoper-atingconditionsinordertoobtaingoodproductqualityandhighprocessefficiency.

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10 Physical and Thermal Properties of Sweet Goods

Shyam S. Sablani

Contents

10.1 Introduction................................................................................................. 19210.2 MeasurementTechniques............................................................................ 193

10.2.1SpecificHeat.................................................................................... 19310.2.1.1MixingMethod.................................................................. 19310.2.1.2DifferentialScanningCalorimeter(DSC)......................... 194

10.2.2ThermalConductivity...................................................................... 19410.2.2.1Steady-StateTechniques..................................................... 19410.2.2.2TransientTechniques.......................................................... 195

10.2.3ThermalDiffusivity......................................................................... 19610.2.3.1IndirectorCalculationMethod.......................................... 19610.2.3.2TemperatureHistory.......................................................... 19610.2.3.3ProbeMethod..................................................................... 197

10.2.4Density............................................................................................. 19710.2.4.1SpecificGravityBottle/Pycnometer................................... 19710.2.4.2SolidDisplacementMethod............................................... 19710.2.4.3GeometryCuttingTechnique............................................. 198

10.2.5MoistureDiffusivity........................................................................ 19810.3 DataCompilationandPredictionModels................................................... 198

10.3.1SpecificHeat.................................................................................... 19810.3.2ThermalConductivity......................................................................20510.3.3ThermalDiffusivity.........................................................................20610.3.4Density/SpecificVolume..................................................................20610.3.5MoistureDiffusivity........................................................................207

10.4 TheoreticalModels.....................................................................................20810.5 Conclusions.................................................................................................20810.6 Acknowledgment.........................................................................................209References..............................................................................................................209AppendixA............................................................................................................ 213

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0. IntroduCtIon

Intheprocessofbaking,heatistransferredprimarilybyconvectionfromtheheatingmediumandbyradiationfromovenwallstotheproductsurface.Thisisfollowedbyconductiontothegeometriccenter.Atthesametime,moisturediffusesoutwardtotheproductsurface.Thetemperatureandmoisturedistributionwithintheporousstructurecanbepredictedusingappropriatediffusionequationsofheatandmoisturetransport.Inordertopredictthetemperatureandmoisturedistributionintheproductduringbaking,knowledgeoftheproductpropertiesisneeded,includingphysical,thermal,andmoisturetransportasafunctionofprocessingconditions(Rask,1989;Sablanietal.,1998).Thesepropertiesareapparentdensity(orspecificvolume),spe-cificheat,thermalconductivity,thermaldiffusivity,andmoisturediffusivity.

Mathematicalmodelingandcomputersimulationbasedonnumericalanalysishavebecomethemaintoolsforunderstandingandpredictingprocessingphenom-ena.Withtheadventofhigh-speedcomputersandinexpensivememory,physical,thermal,andmoisture transportpropertiesofproductscanbe treatedas time-ortemperature-dependent variables instead of average values for the whole process(McFarlane,2006;Sablanietal.,1998). Inaddition,during thebakingprocess,aseries of physical, chemical, and biochemical changes occur in a product. Thesechanges include volume expansion, evaporation of water, formation of a porousstructure,denaturationofprotein,gelatinizationofstarch,formationofcrust,andbrowning reaction.Afundamentalunderstandingofsuchphysical,chemical,andbiochemical changes will be particularly useful in the development of completemathematicalmodelsofthebakingprocess.

Thecompositionoffoodpropertiesaffectsphysical,thermal,andmoisturetrans-portpropertiesofdoughandbatter.Inrecentyears,therehasbeenworldwideinterestinfoodscontainingsubstanceswithbiologicalactivityrelatedtodiseasepreventionandhealthpromotion.Foodindustrieshavebeenlaunchingproductswithfunctionalcomponents.GaldeanoandGrossmann(2006)demonstratedthatoathullsmodifiedbytreatmentwithalkalinehydrogenperoxideassociatedwithextrusioncanbeusedinthepreparationofcookies,withoutdamagetosensoryquality.Someresearchersattemptedtouseextrudedorangepulpandsoapwortextracttoimprovenutritionalvaluesandreplaceeggwhite(Larreaetal.,2005;Celiketal.,2007).Rondaetal.(2005)usedpolyolsandnondigestibleoligosaccharidesinplaceofsucrosetoreducethecaloriecontentofspongecake.Severalstudieshavebeencarriedoutshowingthepotentialuseofhydrocolloids inbakeryproducts toprovidedietaryfiberandto impart specific functional properties such as retarding starch degradation andenhancing textureandmoistureretention(Gomezetal.,2007).These ingredientsalsoinfluencethephysical,thermal,andmoisturetransportpropertiesofdoughandbatter.Thepredictionofsuchpropertiesasafunctionofthechemicalcompositionand process conditions can be very useful in mathematical analyses of heat andmoisturetransport.

Bakeryproducts includevarietiesofbreadssuchaswhitebread, tortilla, tan-dooriroti,chapati,andsweetproductssuchascakes,muffins,biscuits,doughnuts,andcookies.Informationaboutthethermophysicalpropertiesofdoughandbakeryproductsduringbaking isscarcewhencompared to thatavailable for fruits,veg-

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Physical and Thermal Properties of Sweet Goods

etables,andmeatproducts.Moreover,informationatvarioustemperature,moisture,anddensitylevelsisnotalwaysreadilyavailable.Rask(1989)revieweddataonther-malpropertiesofbakeryproductsandpredictionmodels,andLind(1991)presentedmeasurementtechniquesandmodelsofthermalpropertiesofdoughduringfreezingandthawing.Baiketal.(2001)presentedacomprehensivereviewofthemeasure-menttechniques,predictionmodels,anddataonthermophysicalpropertiesofbreadandnonbreadproducts.

This chapter focuses on measurement techniques and prediction models onphysical,thermal,andmoisturetransportpropertiesofsweetbakeryproductssuchascakes,biscuits,muffins,andcookies.Dataonphysicalandthermalpropertiesofsweetbakedproductsatdifferenttemperaturesandbakingconditionsarealsogiven.

0. MeasureMentteChnIQues

Themeasurementsofthermophysicalpropertiesrequirebasicknowledgeofheatandmoisturetransport.Mohsenin(1980),Ohlsson(1983),MurakamiandOkos(1989),Rahman(1995),andrecentlyNasvada(2005)presentedagooddescriptionofmeth-ods used for the measurement of thermal properties of food samples. Baik et al.(2001) reviewed measurement techniques applicable to bakery products. The fol-lowingsectiondiscussesonlythoseusedforsweetbakeryproductssuchascakes,biscuits,muffins,andcookies.

10.2.1 sPeCiFiCheaT

Mostcommonlyusedmethodsforthedeterminationofspecificheat(Cp)ofsweetbakeryproductsare themixingmethodordifferential scanningcalorimeter.Theselectionofthepropermeasurementtechniquedependsuponthenatureandsizeofsamplesandthetemperaturerange(Baiketal.,2001).

0... MixingMethod

Inthismethod,asampleandwater,ofknownmasses,aremixedinacalorimeteratpredeterminedtemperatures.Oncethesampleandwaterreachequilibriumtempera-ture(Te),theCp iscalculatedfromthefollowingheatbalanceequation:

m C T T m C T Tcal p cal i cal e samp p samp i samp, , , ,−( ) + − ee w p w e i w lossm C T T Q( )= −( ) +, ,

(10.1)

wheremisthemass;Cpisspecificheat;andsubscriptscal,samp,andwarecalo-rimeter, sample, andwater, respectively.Ti andTe are the initial and equilibriumtemperatures,andQlossistheenergylossfromortothesurroundings,whichmaybepositiveornegative.Thermalinsulationisgenerallyprovidedtoreduceheatlossfrom or to the surroundings. If the sample is dissolved in water, the enthalpy ofsolutionshouldbetakenintoaccountintheheatbalanceequation.Inthiscase,anindirectmethodcanbeusedtoavoiddirectcontactwithwater.Themainadvantagesofthismethodarethatapplicationissimpleandthatlargesamplescanbeused.The

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methodisparticularlysuitableforheterogeneousfoods.Themeasuringtimescan,however,belong.ThismethodgivesameanvalueofCp overatemperaturerange.Therefore,thetechniqueisnotsuitableforthemeasurementoftemperature-depen-dent specificheat.Theexperimentaluncertainty in themeasuredspecificheatofcookiedoughusingthismethodwasintheorderof5%,whichincludestheuncer-taintiesinthetemperaturemeasurements,themassofdough,themassofwater,andtheheatloss(KulackiandKennedy,1978).

0... differentialscanningCalorimeter(dsC)

The specific heat of homogeneous materials at specific temperatures over a widetemperaturerangecanbedeterminedusingDSC.Nonhomogeneoussamplesrequireseveral replicationsdue to thesmall samplesize (mg)used.Theamountofenergyneededtochangethetemperatureofthesampleiscomparedwiththeenergyneededtochangethetemperatureofareferencematerialatthesamerate(Baiketal.,2001;Rah-man,1995).DSCcanbeusedeitherforscanningoverawidetemperaturerangeorforstepwise(isothermal)measurementswherethetemperatureisalteredinsmallsteps.Recently, a modulated DSC (MDSC) technique was used to measure values ofCpmoreaccurately.InMDSC,amaterialisexposedtoalinearheatingprocessthathasasuperimposedsinusoidaloscillation(temperaturemodulation),resultinginacyclicheatingprofile.Temperaturemodulation(sinusoidaloscillation)oftheMDSCsepa-ratestotalheatflowintoitsreversing(specificheatrelated)andnonreversing(kinetic)components.Thus,specificheatvaluesobtainedbyMDSCaremore precisethanthoseobtainedwithconventionalDSC.Heatingrate,modulationperiod,andamplitudearethemainvariablesinthemeasurementofCp withMDSC(Baiketal.,1999,2001).

10.2.2 ThermalConduCTiviTy

Themeasurementmethodsofthermalconductivity(k)canbeclassifiedassteady-stateandtransientmethods.Steady-statemethodsarenotsuitablefortheassessmentofthermalconductivityofbakeryproductsduetotheirlongertesttimes,whichcanresultinmoisturemigration,andpropertychangesduetolongexposuretohightem-peratures.Transienttechniquesaremore acceptedandappropriatebecausetestingisveryfastandyieldsaccurateresults.

0... steady-statetechniques

10.2.2.1.1 Guarded Hot Plate MethodInthismethod,thesampleisplacedbetweenaheatsourceandaheatsink.Atime-independentheatflowisgenerated(ASTM,1955).Thissystemismathematicallysimpletoprocessandeasytocontrolexperimentally.Thek valuecanbecalculatedusingFourier’sheatconductionequation.Theestimatedvalueofkistakenasameanvaluemeasuredoverthetemperatureintervalusedintheexperiment.KulackiandKennedy (1978) reported an experimental uncertainty of <7.4% in the measuredthermalconductivityofbiscuitdough.Theyattributedthisdeviationtoinstrumenta-tionerrors,geometricaluncertainties,anddeviationsfromtheassumedone-dimen-sionalnatureofheatflow.

52748.indb 194 2/6/08 2:27:00 PM



10.2.2.1.2 DSC Attachment MethodBuhariandSingh(1993)usedanattachmenttoaDSCforthedeterminationofther-malconductivity.Themainadvantagesofthismethodwererelativelyshortdurationofmeasurement(10to15min),smallsamplesize,andnomoisturelossinthesam-ples.Thethermocoupleprobewasusedforthemeasurementofthesampletempera-ture.TheDSCheatingpantemperaturewaskeptat40°C.After5min,theinitialtemperatureofthesamplewasrecorded.Thepantemperaturewasthenimmediatelyincreased by 10°C. After 10 to 15 min, a new steady state existed, and the finalsampletemperaturewasrecorded.Thenk wasobtainedusingthefollowingequa-tion,whichisbasedonFourier’sheatconductionequation:

k L Q

A T T=

−∆

∆ ∆( )2 1 (10.2)

whereListhesamplelength,∆Qisthedifferenceofenergyrequiredtomaintainpantemperature,Aisthesampleareaperpendiculartoheatflow,∆T2isthe finaltemper-aturedifferencebetweenDSCheatingpanandsample,∆T1isthe initialtemperaturedifferencebetweenDSCheatingpanandsample(Baiketal.,2001).

10.2.2.1.3 Capped Column Test DeviceZhouetal.(1994)builtacappedcolumntestdevicetomeasurethermalconductiv-ity.Aconstantsteadyheatfluxwasappliedonthesampleduringtheexperiment.Thesamplewasplacedinthemetalcylindercappedfrombothsides,andtherewasnomoistureloss.Steadyheatfluxwasprovidedbycirculatinghotandcoldwateratconstanttemperaturesatthetwoendsofthecylindricaltestsample(diameter3cm,height5cm,and2.5cm).Thecylindercontainingsamplewasenclosedinpolysty-renefoamtominimizeheatlosstothesurroundings.Thecappedcolumntestdevicewaskepthorizontalduringtheexperimenttoeliminatethegravity-inducedmigrationofmoisturewithinthesample.Thesteadyfluxresultedintemperatureandmoisturegradientsinthesample.Oncethesteadystatewasreached,temperaturesatseverallocationsalongtheheightofthetestsampleandwaterstreamweremeasured.Thenthesamplewascutintoseveralsectionsofequalheightstodeterminethemoisturecontentdistributionbymeasuringthemoisturecontentofeachsection.Thek valuecanbedeterminedbyapplyingsimultaneousheatandmoisturetransferequationstotheexperimentaltemperatureandmoisturegradientdata.Thedeterminationisfast(withinseveralminutes).Thereisnoconcernaboutexperimentaldeviationduetoamoisturegradient,becausethedeviceanddataanalysisaredesignedtoevaluatethermalandmasstransferpropertiessimultaneously(Baiketal.,2001).

0... transienttechniques

Inthetransientmethods,thesampleissubjectedtoatime-dependentheatflow.Tem-peratureismeasuredatoneormorepointswithinthesampleoratitssurface.Themethodrecommendedformostfoodapplications,includingbakeryproducts,isthelineheatsourceprobe.Thetechniqueissimpleandfast(i.e.,3to600s)andrequiresrelatively small samples.However, it does require adata acquisition system.The

52748.indb 195 2/6/08 2:27:01 PM



probe(0.66mmoutsidediameter)consistsofaconstantanheaterwireandchromel-constantanthermocouplewire.

Thebasictheorybehindtheuseofthelineheatsourceprobewaspreviouslydis-cussedbyseveralauthors(Nasvada,2005;Rahman,1995).Alineheatsourceprobeisembeddedinthesample(regardedasaninfinitebody),whichisinitiallyatauni-formtemperature,resultinginaradialtemperaturedistribution.Afterequilibriumisreached,theprobeheaterisenergized.Heatingandtemperaturesaremonitoredsimultaneously.Therateoftemperatureriseoftheheaterisdirectlyrelatedtothesample’sconductivity.TheslopeofthelinearportionofeachdatasetwasusedtodetermineeffectivethermalconductivitybyEquation10.3:

k Q t tT T

=−

4

2 1

2 1πln( / )

(10.3)

where kisthethermalconductivityofthesample;t1istheinitialtimewhentheprobeheaterwasenergized;t2isthefinaltimesinceprobeheaterwasenergized;T1isthetemperatureoftheprobethermocoupleattimet1;T2isthetemperatureoftheprobethermocoupleattimet2;andQistheheatfluxgeneratedbytheprobeheater.

Inordertoobtaincorrectresultsinalineheatsourceprobemethod,probesizeandsamplesizeshouldbecarefullyselected.Insertingaprobeintoanunstablestruc-ture,asdoneindoughandpartlybakedproducts,canalsointroduceerrors.Ruptureofthestructureclosetotheprobecangiverisetofalsevalues.Thus,theuseofalinearmovementprobeholder is strongly recommendedfork measurementusingthistechnique.Othertransientmethodssuchastemperaturehistoryandtransienthotstripmethodshavebeenusedtomeasurethermalconductivityoftortillaandbreaddough(Baiketal.,2001).

10.2.3 ThermaldiFFusiviTy

0... IndirectorCalculationMethod

Thermaldiffusivity(α)canbeestimatedfromexperimentallymeasuredvaluesofthermalconductivity,specificheat,anddensity(ρ).Thisisapreferredwayofdeter-mining thermal diffusivity. In this scheme, the estimation deviation will dependmainlyonthemeasurementofthermalconductivity,specificheat,anddensity(Baiketal.,2001).

αρ

=kC p

(10.4)

0... temperaturehistory

Thisisthemostwidelyusedexperimentalsystemformeasurementofthermaldif-fusivity of bakery products. The experimental apparatus and analytical solutionoftransientheattransferweredescribedbyDickerson(1965)andRahman(1995).

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Inthistechnique,transienttemperaturesarecollectedatthesurfaceandcenterofstandardcylindricalgeometry.Thermaldiffusivityiscalculatedusingthefollowingsolutionofthetransientheattransferequation:

α =

−ΩRT Ts c

2

4( ) (10.5)

whereΩistheconstantrateoftemperatureriseatallpointsinthecylinder(dT/dt,°C/s),RisthesampleradiusandTs−Tcisthemaximumtemperaturedifferenceortheestablishmentofsteady-stateconditionswhenthe temperaturegradientatanylocationinthesampleisnolongertimedependent.

0... ProbeMethod

Nixetal.(1967)mentionedthatthelineheatsourceprobemethodcanalsobeusedtomeasurethermalconductivityanddiffusivitysimultaneously.Itcanbedonebyaddinganextratemperaturesensorsomedistanceawayfromtheheater.Itslocationshouldbeinthefollowingrange:

0 32 6 2. .ατ ατ< <rd (10.6)

whererd isthedistanceofthethermaldiffusivitysensorortemperaturesensorfromtheprobeheater,andτisthetimetestduration.

Thismethodissuitableforliquids,suchascakebatter,orwetingredients,andnonporous soft solids such as biscuit or bread dough. However, it is not suitableforporousstructuresamplesinwhichsignificantvolumeexpansionoccurs,suchasbread,cake,andmuffin.

10.2.4 densiTy

0... specificgravityBottle/Pycnometer

Thedensity(ρ)ofasampleinaliquidorsemisolidstatecanbemeasuredeasilybyspecificgravitybottleorpycnometer.The sample isplaced in a containerwhosevolumeisalreadyknown,andthenthemassofthesampleisdetermined(Rahman,1995).Densitycanbecalculatedfrommassandvolumedata.

0... soliddisplacementMethod

Thevolumeof irregular(dryandbaked)samplecanbeestimatedusingthesoliddisplacementmethod.Inthismethod,asampleofknownmass(Ms) iscoveredwithseedsinacontainer,andthewholeisweighed(Mc+sd+s).Thebulkdensity(ρs) ofafineseedisdeterminedpriortothetest.Themassofthecontainer(Mc)isknown;thus,thevolumeofthesample(Vs) canbeevaluatedbythefollowingequation:

V V

M M Ms container

c sd s c s

s= −

− −

+ +

ρ (10.7)

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Thistechniqueisverycommonfordensitymeasurementofmostfinalbakeryproducts. Rapeseed (Rubio and Sweat, 1990) and amaranth seed (Moreira et al.,1995)havebeenassessed.

0... geometryCuttingtechnique

Finalbakedgoodscanbecutintotheshapeofregulargeometries.Thevolumeiscalculatedfromthedimensionsofthesample.Typically,bakedsamplesarefrozenimmediatelyaftertheprocess.Frozensamplesarethenusedtocutintoevensidesofregulargeometry,suchascubeorrectangularshapes(Baiketal.,1999).Themassofthepiecescanbeeasilyobtained,andthenthedensitycanbecalculatedfromthemassdividedbythevolume.

10.2.5 moisTurediFFusiviTy

Duringbaking,asthebattertemperatureincreases,volumeexpansionoccursduetothechemicalleaveningagent,theincorporationofair,andwatervaporization.Thevolumeincreasesuptoaroundtwothirdstothreequartersofthebakingtime.Then,itdecreasestosomeextent(BaikandMarcotte,2003).Thevolumechangehastobetakenintoaccountinthedeterminationofthemoisturediffusivity.

BaikandMarcotte(2003)usedananalyticalsolutionofaninfiniteslabbasedontheconstantvolumeandmoisturediffusivity.Thesolution,however,incorporatedtheeffectofvolumechangeassuggestedbyCrank(1975)andGekasandLamberg(1991).Theyestimatedmoisturediffusivitythroughthefirstfallingrateperiodfromplottingthedimensionlessmoistureratioagainsttimeonasemilogscale.TheyusedanArrheniustypeofequationtomodeltheeffectoftemperatureandmoisturecon-tentonthemoisturediffusivity.

0. dataCoMPIlatIonandPredICtIonModels

Thephysical,thermal,andmoisturediffusionpropertydataandpredictionmodelsofsweetbakedproductsarepresentedinTable10.1andTable10.2.Thepropertydatawereclassifiedbyproduct,moisture,andtemperature.

10.3.1 sPeCiFiCheaT

Specificheatofcommercialbiscuitdoughwasmeasuredusingthemixturemethodatthreedifferenttemperatures(29.8,35,and37.9°CforAACCdough;30,36.5,and39°Cforhardsweet[HS]dough)byKulackiandKennedy(1978).Thespecificheatofbothtypesofdoughincreasedwithincreaseintemperature.TheindirectmixingmethodwasusedbyHwangandHayakawa(1979)tomeasurethespecificheatofbiscuitandcracker.Thetechniqueallowedthemtomeasurethespecificheatattem-peraturesabove100°C.Sampleswerecollectedfromtwolocationsinamultizonebandoven.Foramoisturecontentvaryingfrom3.15to3.87%,specificheatforbis-cuitrangedfrom1875to1942.7J/kgK.

Christensonetal.(1989)andBaiketal.(1999)usedDSCtomeasurethespecificheatofcommercialmuffin,biscuit,andcupcake(Table10.1andTable10.2).Chris-

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Physical an

d Th

ermal Pro

perties o

f Sweet G

oo

ds

taBle0.PhysicalandthermalPropertiesofsweetBakeryProducts

Product temperature(°C)MoistureContent

(%w.b.)density(kg/m)

specificheat(kj/kgK)

thermalConductivity

(W/mK)

thermaldiffusivity(m/s)×0

technique ref.

Biscuit 3.15 1875Cp:indirect

mixingmethod

HwangandHayakawa

(1979)3.53 19433.87 1934

BiscuitdoughAACCdough

29.8–37.9a24.5–45.1b

4.1 1252±18 2835–3128 0.405±0.22 8–12

Cp:mixingmethod

k:singleplatemethod

α:calculationmethod

KulackiandKennedy(1978)

HS(hardsweetdough)

30–39a24.9–35.6b 8.5 1287±9 2420–3182 0.39±0.037 8–12

Biscuit2mmfrombottom5mmfrombottom

0.070.16k:hotplatesteady

stateStanding(1974)

YellowcakebatterEdgeCenter

41.534–4035.5–39

694285–815300–815

29502800

0.2230.239–0.1190.228–0.121

10.98.6–15.08.6–14.3

k:lineheatsourceprobe

Sweat(1973)

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00 Fo

od

Engin

eering A

spects o

f Bakin

g Sweet G

oo

ds





thermalConductivity

(W/mK)


technique ref.

Cupcakebatter4min6min13min15min19.5min

20±1.220±1.254±7.020±1.268±5.720±1.2102±120±1.2103±220±1.2104±2

34.6±1.9333.9±1.6933.9±1.6933.5±1.1633.5±1.1630.0±1.4630.0±1.4630.3±1.7330.3±1.7327.6±2.0627.6±2.06

803±12.0915±18.6662±0.91120±20558±9.0236±23.4236±23.4282±17.8281±17.8287±14.6287±14.6

2517±112

2599±49.3

2629±27.8

2658±106

2658±46

2613±53.9

0.206±0.0070.216±0.0110.187±0.0050.283±0.0170.196±0.0140.0703±0.0030.106±0.0120.0683±0.0050.116±0.0120.0683±0.0040.120±0.007

10.2+0.96

10.8+0.49

13.3+1.31

17.0+4.43

15.4+2.86

16.0+2.06

Cp:MDSCk:lineheatsourceprobeα:calculationmethod

Baiketal.(1999)

Muffin 17 441 2779 0.70 57.6

Cp:calculatedfromprediction

modelk:calculatedasαρ

Cpα:temperaturehistory

TouandTadano(1991)

Whitelayercake3.25min4.1min9.0min10.5min7.0min8.6min3min6min3min6min

MWat50%powerIRat50%powerIRat70%powerMW(50%)+IR(50%)MW(50%)+IR(70%)

122011111020785950785860700830740

ρ:soliddisplacementmethod

Sumnuetal.(2005)

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Physical an

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ermal Pro

perties o

f Sweet G

oo

ds

0





thermalConductivity

(W/mK)


technique ref.

Spongecake Porosity=0.39 880 1950 0.15Mass

permeability=4.9×10−13m2

Lostieetal.(2004)

YellowlayercakeBatterControlAlginateCarrageenanLocustbeanGuarHPMCPectinXanthanCakeControlAlginateCarrageenanLocustbeanGuarHPMCPectinXanthan

10201055112710631127111510551800435448405385426411412381

ρ:measuringcylinder

Gomezetal.(2007)

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0 Fo

od

Engin

eering A

spects o

f Bakin

g Sweet G

oo

ds





thermalConductivity

(W/mK)


technique ref.

SpongecakeBatterControlSE25SE50SE75W25W50W75CakeControlSE25SE50SE75W25W50W75

710740750770810880850232248253254299297293

Celiketal.(2007)

CookiesControl5%orangepulp15%orangepulp25%orangepulp

48545778645741763

813Larreaetal.

(2005)

SpongecakeControlMaltitolMannitolSorbitolXylitolIsomaltoseOligofructosePolydextrose

242292356255262286256290


Rondaetal.(2005)

AngelfoodcakeLEW/WPI100/0100/0100/0100/0100/0100/075/2575/2575/2550/5050/5050/5050/50

Airpressure(bar)00.50.050.10.51.00.050.050.10.050.51.01.5

Oventemperature190190180180160160190180180190190190190

186286209231277348206208220329481497605


Morretal.(2003)

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Physical an

d Th

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perties o

f Sweet G

oo

ds

0taBle0.PhysicalandthermalPropertiesofsweetBakeryProducts




thermalConductivity

(W/mK)


technique ref.

CakeWheatcontrol15%Barley15%Millet15%Rye15%Sorghum

400426417456426


RagaeeandAbdel-Aal(2006)

CookiesUntreatedoathullsTreatedoathullsc

505450

Galdeanoetal.(2006)

CakeBatterCrumb

41.535.5700300

29502800

0.220.12

1114

Rask(1989)

BiscuitRotationspeedd2503505001000Durationd1min5min20min40min80min

6.15.76.06.56.56.15.85.76.5

247257246271227241258270279


Edoura-Gaenaetal.(2007)

a Measurementtemperaturefor Cp.b Measurementtemperaturefork.c SE25,SE50,andSE75areeggwhiteproteinreplacedwithsoapwortextractby25,50,and75%,respectively.W25,W50,andW75areeggwhiteproteinreplacedbywater

by25,50,and75%,respectively.LEWisliquideggwhite;WPIiswheyproteinisolates.d 15gWPI/100gsolution.e 11gWPI/100gsolution.f Chemically(alkalinehydrogenperoxide)andphysically(extrusion)treated.g Duringtheaerationstep.

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tensonetal.(1989)determinedthespecificheatatatemperaturerangeof20to85°Cforthesampleshavingmoisturecontentbetween0and60%.Togetvariousmoisturecontentlevels,wetsampleswereeitherairdriedormicrowaveovendriedforappropri-atetimes.Baiketal.(1999)bakedsamplesinapilot-scaleelectricovenatatempera-ture/timecycle(177°C/19.5min)thatproducedphysicalpropertiessimilartoacakebakedinanindustrialoven.Duringbaking,thesampleswereremovedatspecificbak-ingtimes(0,4,6,13,15,and19.5min).SamplespecificheatsweredeterminedusingMDSC.Then,10to15mgofsampleswerescannedataheatingrateof3°C/minoverthetemperaturerangeof20to110°C.An80-smodulationperiod(singlecycle)and1°Camplitudewereused.Theyobservedthatthespecificheatofcakebatterincreasedfrom2516.8J/kgKto2658J/kgKafter13minbaking time,and thendecreased to2613J/kgKbytheendofbaking.Specificheatincreasedwithrisingtemperatureanddecreased with reducing moisture. After 13 min of baking, the temperature of theproductremainednearlyconstant,butthemoisturecontentcontinuedtodecrease.Asaresult,asmalldecreaseinthespecificheatofthecakewasobserved.Thetraditionalmass fractionmodelwas applied to their experimental data, but it didnotfit theirexperimentaldatawell.UsingaPROCGLM,amodelforspecificheatwasdevelopedasafunctionofmoisturecontentandtemperature.Thespecificheatofacupcakewas

taBle0.PredictionModelsforPhysicalandthermalPropertiesofsweetBakeryProducts

Product equation referenceMuffin Cp=[0.40+0.0039T]×103,298–358K;R2=0.96 Christensonetal.(1989)

BiscuitCp=[0.80+0.0030T]×103,331–358K;R2=0.95Cp=[1.17+0.0030T]×103,303–331K

Muffin

lnk=−48.0−10.9m+0.272T+0.053mT−4.1×10−4T2;R2=0.917

lnk=−7.79−7.80m+0.015T+0.043mT;R2=0.904

Biscuit

lnk=−15.8−7.90m+0.072T+0.038mT−9.7×10−5T2;R2=0.819

lnk=−5.95−8.61m+0.0098T+0.041mT;R2=0.820

Yellowlayercake

Cp=[1.0−0.5(1-m)]CpwSweat(1973)

Cakek=0.0844+0.0000892ρ;standarddeviation:0.0073

RubioandSweat(1990)

Cupcake

Cp=7107m+18.7T−45.3mT;R2=0.999

Baiketal.(1999)k=0.00263T−0.831m−0.00091ρ+0.00422mρ;R2=0.991

α=2.55×10−8m−1.75×10−10

ρ−3.95×10−10T+2.42×10−7;R2=0.971D=29.6εexp(−8020/T) BaikandMarcotte

(2003)

Note:Wheremismoisturecontent,Tisthetemperature,εistheporosity,andCpwisthespecificheatofwater.

52748.indb 204 2/6/08 2:27:06 PM


Physical and Thermal Properties of Sweet Goods 0

affected significantly (p < 0.001) by moisture content and temperature. Interactioneffectsofthetwovariableswerealsosignificant(p<0.001).Sweat(1973)estimatedthespecificheatofyellowlayercakebyassumingthatCp forthenonwaterfractionwashalfofthatofwater.Duringbaking,thespecificheatdecreasedslightlyfrom2950J/kgKofthebatterto2800J/kgKofthefullybakedcake.

10.3.2 ThermalConduCTiviTy

Standing(1974)estimatedthethermalconductivityinbiscuitsusingaguardedhotplatesteady-stateprocess.Thetemperatureswererecordedattwolocations,2and5mm,fromthebase.Duringthesemeasurements,thebiscuitswereheatedonlybyconductionfromahotplate.Theplatetemperaturewasvariedfrom159to208°C,and the thermal conductivitywascalculated fromaheatbalanceover theheatedplateandbiscuit.Thus,thecalculatedconductivityincludedtheresistancetoheattransferbetweentheplateandthesurfaceoftheproduct.

A significantdifferenceinthermalconductivitybetweentwopositionswasseen(5mmfromthebase:0.16W/mK,2mm:0.07W/mK).Standing(1974)alsofoundthethermalconductivitytobelowerathigherplatetemperature.Thermalconduc-tivityofcommercialbiscuitdoughwasdeterminedbyasingle-platemethodbasedon a steady-state method and was measured at several temperatures between 24and64°C(KulackiandKennedy,1978).The thermalconductivityof twodoughsfirst increasedwith temperature (AACC:<31.9°C,HS:<30.4°C), thendropped torelativelyconstantvaluesathighertemperatures.Theincreaseofthethermalcon-ductivityofwaterwithtemperatureaccountsfortheinitialincreaseinthethermalconductivity of the dough. However, the decrease in the thermal conductivity athighertemperaturescouldnotbeexplained.

Sweat(1973)usedalineheatsourceprobetomeasurethethermalconductivityofyellowlayercakebakedatdifferenttemperaturesandatdifferentlocations.Thesampleswerecooledtoabout28°Cbeforemeasurement.Duringbaking,thethermalconductivitydecreasedfrom0.223W/mKinthebatterto0.121W/mKattheendofbaking.Halfwaythroughbaking,thethermalconductivityatthecakeedgeshowedlowervaluesthanatthecenter.RubioandSweat(1990)measuredthethermalcon-ductivityofthreetypesofcakeatroomtemperatureusingalinesourceprobe.Thewatercontent(34.64to41.13%)didnotinfluencethethermalconductivity,buttheyfoundapositivecorrelationbetweenthermalconductivity(about0.058to0.14W/mK)anddensity(about85 to540kg/m3).Themodeldevelopedbasedonexperimentaldatayieldedbetterpredictionsthantheoreticalmodelssuchastheparallelmodel.

Baiketal. (1999)measured the thermalconductivityofacupcakeat specificbakingtimes.Moisturecontent,density, temperature,andtheinteractionbetweenmoisturecontentanddensityhadsignificanteffects(p <0.002)onthermalconduc-tivityofcupcakesduringbaking.Thepredictionaccuracyoftheirmodelwashigherthanthatofmodelsreportedformuffin(Christensonetal.,1989)andcake(RubioandSweat,1990).

Usingalineheatsourceprobe,Christensonetal.(1989)measuredthethermalconductivityofmuffinandbiscuitatatemperaturerangeof20to85°Candamois-turecontentrangeof0 to60%.Thermalconductivitydataforbiscuithadgreater

52748.indb 205 2/6/08 2:27:07 PM



variationthanformuffin.Thevariationwascausedbynonhomogeneityofbiscuit.TouandTadano(1991)estimatedthermalconductivityofmuffinfromthermaldif-fusivity,density,andspecificheat.Thecalculated thermalconductivityofmuffinwas0.706W/mK.

Themodelsdevelopedforthepredictionofthermalconductivityaremostlyprod-uctspecific(Table10.2).Aneural-network-basedmodelwasdevelopedbySablanietal.(2002)forcalculatingthermalconductivityofavarietyofbakeryproductsunderawiderangeofconditionsofmoisturecontent,temperature,andapparentdensity.The developed model (Appendix A) can easily be incorporated in the numericalanalysisofheatandmoisturetransferduringbaking.

10.3.3 ThermaldiFFusiviTy

KulackiandKennedy(1978)usedanindirectmethodtocalculatethethermaldif-fusivityofcommercialbiscuitdough.Thethermaldiffusivityvariedfrom8.0to12.0×10−8m2/sintherangeofmoisturecontent4.1to8.5%,density1252.3to1286.6kg/m3.Thetotaluncertaintyinthethermaldiffusivityoftwobiscuitdoughswasatmaximum13.4% (AACC)and15%(HS).Sweat(1973)estimatedthethermaldif-fusivityofyellowlayercakefrombulkdensity,thermalconductivity,andspecificheat. It increased from1.09×10−7 to1.43×10−7m2/s for the centerof the cakeduringbaking.Changesweremoresignificantat theedgeof thecake thanat thecenter.Baiketal.(1999)alsoestimatedthethermaldiffusivityofacupcakeusinganindirectmethod.Theinitialthermaldiffusivityofbatteratroomtemperaturewas1.02×10−7m2/s.Thethermaldiffusivityincreasedto1.696×10−7m2/sbytheendofbakingwithamaximumof1.698×10−7m2/safter13min.ThesechangesweresimilartothosereportedbySweat(1973).

Baiketal.(1999)alsodevelopedapredictionmodelofthermaldiffusivitydur-ingsimulatedbakingasafunctionofdensity,temperature,andmoisture.Thetem-peraturehistorymethodwasusedtoobtainthethermaldiffusivityofmuffin(TouandTadano,1991).Sampleswereputintoacylindricalcontainer(diameter80mm,height30mm)andbakedat220°C,andthetemperatureofthecenterofdoughwasmeasured.Thethermaldiffusivityvalueobtainedwas5.76×10−7m2/s.

10.3.4 densiTy/sPeCiFiCvolume

Thechangesindensityfollowthevolumetricchangeintheproductduringbaking.Sweat(1973)reportedthatduringbaking,thevolumeincreasedupto70%duetoformationofgasthatoccurredfromtheactionofchemicalleavening.Thisresultedinadensitydecreaseofabout75%attheendoftheprocess.

Christensonetal. (1989)measured thedensityof interiorportionsofsamplesbythegeometrycuttingtechnique.Baiketal.(1999)usedpycnometerandgeom-etrycuttingtoestimatethedensityofcakebatter/semisolidbatterandbakedcake,respectively.Theyusedfrozensampleandasharpknifetoprepareregularshapes.Thesampleswereweighed,andafterthawing,eachdimensionwasmeasuredtocal-culatevolume.Theyreportedthatthebatterdensitydecreasedsharplyfrom803to236kg/m3 during 13minofbaking.Itthenincreasedto281kg/m3after15minduetocollapse.Afterthat,itremainednearlyconstanttotheendofbaking.

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Severalresearchershaveusedthesolid(seed)displacementmethodtomeasurethevolume/densityofbakedproducts(Gomezetal.,2007;Morretal.,2003;RagaeeandAbdel-Aal,2006;Rondaetal.,2005;Sumnuetal.,2005).Specificvolume/den-sitywasusedasaqualityindextostudytheinfluenceofdifferentingredientsandoperatingconditionsonbakedproducts.Morretal.(2003)studiedtheinfluenceofappliedairpressureintheoventoimprovebakingpropertiesofwheyproteinisolate(WPI)inangelfoodcake.Cakesbakedwith75%liquideggwhiteand25%WPIwithvariableairpressureexhibitedimprovedphysical,textural,andsensoryproper-tiescomparedtothosebakedatatmosphericpressureorconstantairpressure.

Edoura-Gaenaetal.(2007)demonstratedthatthespeedandaerationdurationhadasignificanteffectonthedensityofbiscuits.Thedensityincreasedfrom247to271kg/m3and227to279kg/m3asthespeedofrotationincreasedfrom250to1000rpmanddurationfrom1to80min,respectively.Rondaetal.(2005)assessedthe effect of polyols and oligosaccharides on various quality attributes includingdensityandspecificvolumeofsugar-freespongecakes.Theyfoundthatxylitolandmaltitolproducedspongecakesmoresimilartothecontrolwhichwasmanufacturedwithsucrose.ThefunctionalityofdifferenthydrocolloidsonthequalityofyellowlayercakewasstudiedbyGomezetal.(2007).Theyreportedthatincorporationofhydrocolloidledtoyellowlayercakeswithhighervolumethanthecontrol,exceptwhenalginatewasused.Cakeswiththehighestvolumewereobtainedwithxanthangumfollowedbylocustbeangum.

An experimental study by Celik et al. (2007) showed that egg white proteincanbepartiallyreplacedwithsoapwortextractinthespongecakeformulationwithonlyasmallchangeinthedensityofthefinalbakedproduct.Larreaetal.(2005)partiallyreplacedwheatflourwithextrudedorangepulpandproducedcookieswithacceptedflavorandtexturalquality.Thespecificvolumevariedfrom1.23to1.55astheamountoforangepulpdecreasedfrom25to5%.GaldeanoandGrossmann(2006)demonstratedthatphysicallyandchemicallymodifiedoathullscanbeusedtopartiallyreplacethewheatflourincookiesinordertoimprovethefibercontentwithoutmodificationofphysicalandsensoryproperties.Sumnuetal.(2005)usedmicrowaveandinfrared(IR)aloneandincombinationforthebakingofcakes.Thecake specificvolumewas lowwhenmicrowaveand infraredalonewereused forbaking.TheyshowedthatimprovedqualitycakescouldbeobtainedwhenIRheat-ingwascombinedwithmicrowaveheating.Byusing IR–microwavecombinationbaking,both the time-saving advantagesofmicrowaveand the surfacebrowningadvantageofIRcanbeobtained.Thespecificvolumealsoimprovedsignificantlybyusingmicrowaveandinfraredincombination.

10.3.5 moisTurediFFusiviTy

BaikandMarcotte(2003)estimatedthemoisturediffusivityofcupcakefordiffer-entinitialmoisturecontentsandoventemperatures.Themoisturediffusivityrangedfrom 9.0 × 10−11 to 4.4 × 10−8 m2/s for the industrial cake batter during baking.Temperatureandporositystronglyaffectedtheeffectivemoisturediffusivity(p <0.0001).Asporosityandtemperatureofthebatterincreased,themoisturediffusiv-ityincreased.

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0. theoretICalModels

Severaltheoreticalmodelshavebeenproposedtopredictphysicalandthermalprop-ertiesoffoodsatdesiredconditions.Thesemodelsaremostlybasedonthechemicalcompositionasfollows:

C X Cp iw

pi=∑ (10.8)

k X ki

vi=∑

(Parallelmodel) (10.9)

1k

Xkiv

i=∑

(Perpendicularmodel) (10.10)

ρ

ρ

=

∑1Xi

w

i (10.11)

whereXivandXi

warevolumeandmassfractionofaunitcomponenti.Thesemod-elshavebeenappliedsuccessfullyfordifferentfoodmaterials,andthemodelsofspecificheatanddensityarealsovalidinporousfoods,includingbakeryproducts.Parallelandperpendicularmodelshavebeenfoundtoprovidetheupperandlowerlimitsofthermalconductivity,respectively,ofmostfoodmaterials.However,appli-cationsofsuchmodelstobakeryproductshavebeenlimited.

0. ConClusIons

BoththeDSCandmixingmethodshavebeenfavoredforthemeasurementofthespecificheatofbakeryproducts.Because specificheat is independentofdensity,themassfractionmodelisusuallyemployedforprediction.Forthedirectmeasure-mentof thermalconductivityofbakeryproducts, transient techniquesweremorepredominant. Among these techniques, the line heat source probe was the mostpopular; second was the temperature history method. As the porosity affects thethermalconductivitysignificantly,themassfractionmodelwasnotsuitablefortheestimationofthermalconductivityofbakeryproducts.Thefavoredstructuremodelforair-containingbakeryproductswastheparallelmodel.Thiswasbasedonthevolume fractionof eachcomponentof the sample food.Duringprocessing, thereare great structural changes. Chemical and physical reactions (e.g., phase transi-tion,distillationheattransfer)occuraswellascomplicatedtemperaturehistoryandmoisturecontent.Volumeisincreasing.Veryoften,thesechangesareinteracting.

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Thus,aregressionmodelbasedonexperimentaldataisappliedmorethanastruc-turalmodel.

TheindirectmethodofcalculationfromCp,ρ,andkandthetemperaturehis-torymethodarethemostcommonforthemeasurementofthermaldiffusivity.Thethermaldiffusivityincreasedduringbakingwhilethermalconductivitydecreasedand specificheat changed slightly.Thiswasattributed to themigrationofvapor,structural changes, and thewater-holdingcapacity.Solid (seed)displacementandgeometrycuttingmethodshavebeenusedforthemeasurementofvolumeandden-sityofbakedproducts,andthepycnometermethodhasbeenusedfor thedensitymeasurementofbatter.Moisture-diffusivity-relatedmeasurementshavebeenverylimited.Effortsareneededtodevelopmoregenericcorrelationtopredictphysicalandthermalpropertiesofbakeryproductsunderawidevariationofconditions.

0. aCKnoWledgMent

TheauthorwouldliketoacknowledgetheassistanceofMattheusF.A.Goosen,NewYorkInstituteofTechnology,Amman,Jordan,forprovidingvaluablecommentsonthemanuscript.

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Choi,Y.andM.R.Okos.1986.Effectsoftemperatureandcompositiononthermalproper-tiesoffoods,inFood Engineering and Process Applications: Transport Phenomena, LeMaguer,M.andP.Jelen(eds.),Vol.1,Elsevier:London,93–101.

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Hwang,M.P.andK.I.Hayakawa.1979.Aspecificheatcalorimeterforfoods.Journal of Food Science 44:435–438,448.

Kulacki,F.A.andS.C.Kennedy.1978.Measurementof the thermo-physicalpropertiesofcommoncookiedough.Journal of Food Science 43:380–384.

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gestibleoligosaccaridesonthequalityofsugar-freespongecakes.Food Chemistry90:549–555.

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Sablani,S.S.,M.Marcotte,O.D.Baik,andF.Castaigne.1998.Modelingofsimultaneousheatandwatertransportinthebakingprocess:Areview.Lebensmittel Wissenschaft und Technologie 31:201–209.

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Sweat,V.E.1973.Experimentalmeasurementofthethermalconductivityofayellowcake.Proceedings of 13th International Conference on Thermal Conductivity, 213–216,LakeOzark,MO,November5–7.

Tou,K.andT.Tadano.1991.Studyoneffectivethermaldiffusivityofmuffinduringbaking.Bulletin of the College of Agriculture and Veterinary Medicine, Nihon University48:199–204.

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Appendix ANeural-network-basedequationsforestimationofthermalconductivity,k(W/mK)ofdoughandbakeryproductsasafunctionoftemperature(T,°C),moisturecontent(M,%,wetbasis),andapparentdensity(ρ,kg/m3)(adaptedfromSablanietal.,2002):

X2=T*(0.00856)+(−0.627)

X3=M*(0.0423)+(−1.059)

X4=ρ*(0.00193)+(−1.31)

X5=tanh[(−3.66)+(5.64)*X2+(0.298)*X3+(−1.08)*X4]

X6=tanh[(−0.812)+(−1.33)*X2+(−1.385)*X3+(1.43)*X4]

X7=tanh[(−0.157)+(0.0634)*X2+(0.122)*X3+(0.22)*X4+(−0.686)*X5+(−0.403)*X6]

k=X7*(0.802)+(0.549)

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11 Alternative Baking Technologies

Dilek Kocer, Mukund V. Karwe, Servet Gülüm Sumnu

Contents

11.1 Introduction................................................................................................. 21511.2 JetImpingementOvenTechnology............................................................. 216

11.2.1EngineeringandDesignAspectsofJetImpingementOvens.......... 21711.2.2BakinginJetImpingementOvens...................................................220

11.3 MicrowaveBakingTechnologies................................................................22311.3.1 PrinciplesofMicrowaveBaking......................................................22311.3.2QualityDefectsinMicrowave-BakedProducts..............................22711.3.3StarchGelatinizationinMicrowaveBaking....................................22811.3.4Microwave-BakedCakes................................................................. 22911.3.5Microwave-BakedCookies.............................................................. 231

11.4 HybridTechnologies................................................................................... 23111.4.1 HybridJetImpingementandMicrowaveOvens.............................. 23211.4.2Microwave–InfraredCombinationOvens....................................... 235

11.5 Conclusions................................................................................................. 238References.............................................................................................................. 239

. IntroduCtIon

Bakingtechnologyiscontinuouslychangingtoincreaseenergyefficiencyandsav-ings,andtoimproveproductquality.Today’sovenshaveadvancedfromearliersim-plewoodbakingstovestosophisticatedmicrochip-controlleddevices.Earlierbakingovenswerenaturalconvectionovenswhichwerefollowedbyforcedconvectionandgas-firedovens.Then,microwaveovensandjetimpingementovenswereintroduced.Microwaveovensand jet impingementovensprovidenoticeable improvements inbakingtechnologyandhavebeenstudiedbyresearchersasalternativebakingtech-nologies.Thesestudiesfocusonthefollowing:

1.Understandingtheeffectofusingalternativetechnologiesonthephysico-chemicalchangesoccurringduringbaking,andthephysicalcharacteristicofthefinishedbakedproduct

2. Improvingproductformulationsandovendesignstoovercomeanyprob-lemsassociatedwiththeuseofalternativebakingtechnologies

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3.Definingoptimumprocessingconditionstoobtainproductswithhigh-qual-ityparameters

Thefirstpartofthisbookchaptercoversthesealternativebakingtechnologiesandtheirapplications.Thestudiesonbakingshowthatanysinglemodeofbaking(microwave,naturalconvection,andimpingement)hasitslimitationsaswellasitsadvantages.Theselimitationshavebeenencouragingresearcherstostudycombina-tionbaking.Thecombinationofalternativebakingtechnologieshastheadvantageofproducingahigh-qualityproductwithshorterandmoreefficientprocesses.Thelastpartofthischapterfocusesonthesecombinationoventechnologiesasmicro-waveandimpingementcombinationheating,andmicrowaveandinfraredcombina-tionheating.

. jetIMPIngeMentoventeChnology

Natural convection baking is a slow and inefficient process that results in varia-tions inproductqualitydue tononuniformheat transferover theproduct surface(Henke, 1985; Walker, 1987). Increasing the air movement within the oven withtheuseoffansandblowersimprovestheheattransferratebutstillisnotenoughtoachieveproductuniformity(Henke,1985;Walker,1987).Inordertoprovidemoreuniformdistributionofairovertheproductsurfacecomparedtonaturalconvection,jetimpingementtechnologywasintroduced.Jetimpingementovens,firstdesignedbyDonaldSmith (1975), are a special class of forced convectionovens inwhichhigh-velocity(10to50m/s)jetsofhotair(100to250°C)impingeverticallyonafoodproduct(Figure11.1).

Theimpingementofhigh-velocityairverticallyontotheproductsurfaceresultsinahigherrateofheattransfersothattheproductswithinternalandexternalchar-acterssimilartoconventionallybakedonescanbeproducedatlowertemperaturesandinshortertimes(LiandWalker,1996;Walker,1987).Thisrapidheattransfertechnologyhasbeensuccessfullyintroducedinsmallfast-foodovensaswellascom-mercialtunnelovens(Walker,1987).Jetimpingementovenshavebeenusedinthefoodindustryforthebakingoftortilla,potatochips,pizzacrust,pretzels,crackers,cookies,breads,andcakesandtotoastready-to-eatcereals(LiandWalker,1996;Walker,1987;WalkerandSparman,1989).

fIgure. Amultiplejetimpingementoven.

Conveyor beltor turntable

Jets

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Alternative Baking Technologies

TheheattransferfromanimpingementjetcanbeexpressedbyNewton’sequa-tion(1):

Q hA T= ∆ (11.1)

where Q is the heat transfer rate, h is the heat transfer coefficient, A is the heattransferarea,and∆Tisthetemperaturedifference(K)betweentheproductsurfaceandthejetmedium.Theheattransfercoefficient,h(W/m2K),thatisaffectedbytheairvelocitycanbedeterminedexperimentallyandpredictednumerically(Walker,1987).Theheattransfercoefficientsassociatedwithairimpingementovensare5to20timeshigherthanthoseassociatedwithnaturalconvection(KocerandKarwe,2005; Marcroft and Karwe, 1999; Marcroft et al., 1999; Nitin and Karwe, 2001,2004;Nitinetal.,2006;Walker,1987).Typicalheattransfercoefficientvaluesare6to12W/m2Kfornaturalconvection,13to30W/m2Kforforcedconvectiontoflatsurfaces,and40to200W/m2Kforairimpingement.

11.2.1 enGineerinGanddesiGnasPeCTsoFJeTimPinGemenTovens

Injetimpingementovens,theheatedairisdirectedtothefoodthroughthenozzlesthatcanbesimpleholes,shortnozzles,orlongnozzletubes.Theimportantfactorsthatshouldbeconsideredinjetimpingementovendesignarethedistancebetweenthe impingementnozzleand theproduct surface,nozzlediameterandwidth,andspacingbetweennozzles(OvadiaandWalker,1998).Jetsusedinjetimpingementovensforheatingandbakingoffoodproductsaresubmergedturbulentjetswherethejetfluidisthesameasthesurroundingmedium.

Theflowfieldofanimpingingjethasbeendividedintothreeregions:thefreejetregion,thestagnationregion,andthelateralspreadregion(Figure11.2)(GardonandAkfirat,1965;Sarkaretal.,2004).Thefreejetregionisfurtherdividedintothreesubregions:thepotentialcoreregion,thedevelopingflowregion,andthedevelopedflowregion(Figure11.2).

D Nozzle

Free jet region

Potential core region

Developing flowregionDeveloped flow region

Stagnation pointLateral spreadregion

H

fIgure. Regionsofimpingingjetflow.(ModifiedfromSarkar,A.,Nitin,N.,Karwe,M.V.,andSingh,R.P.,Journal of Food Science69(4):113–122,2004.WithpermissionfromBlackwellPublishing.)

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Inthestagnationregion,theaxialvelocitydecreasesrapidly,andinthelateralspreadregion, theradialvelocityrapidlyincreasesnear thestagnationregionandlaterdecreases(Figure11.3)(MarcroftandKarwe,1999;Marcroftetal.,1999;NitinandKarwe,2004).Ingeneral,forasinglejetimpingingonaflatsurface,theheattransfercoefficientishighatthestagnationregionanditdecreasesalongtheradialdirectionduetoagrowingboundarylayer(DeBonisandRuocco,2005;GardonandAkfirat,1965;Martin,1977;NitinandKarwe,2004;Nitinetal.,2006;Olssonetal.,2004).Thevalueoftheheattransfercoefficientisknowntobeafunctionofnozzle-to-platespacingaswellasReynoldsnumber.Jetsaregenerallylocated2to5timesthenozzlediameterabovetheproduct(Walker,1987).Arecentstudyofnumericalsimulationoffluidflowandheattransferforanimpingementflowonamodelcookieshowed that the maximum heat transfer coefficient is observed at the stagnationpoint(Figure11.4a),andthelocalmaximumshiftsawayfromthestagnationpointforhighz/d(zisnozzle-to-platedistance,anddishydraulicdiameterofthejetatinlet)ratiosathigherjetvelocities(30and40m/s)asseeninFigure11.4b(NitinandKarwe,2004).Anotherinterestingstudythatincorporatedthewatervaportransportmodelshowedthenonuniformityofheatandmasstransferalongtheexposedsur-facewithevaporationanddepletionofliquidwateratthestagnationregionandrapidremovalofsurfacevaporawayfromthestagnationpoint,inducingmorediffusionwithinthefood(DeBonisandRuocco,2005).

Multiple jetshavecharacteristics similar to thoseofa single jet;however, thepossibleinteractionsbetweensurroundingjetsmaydisturbthestagnationregionandleadtoareductionintherateofheattransfer.Theinteractionsbetweenthejetscanleadtostrongreverseflowsor“upwardjetfountains”thatcanresultinsecondaryheattransfermaximaontheimpingingsurfaceduetohighlevelsofturbulence(GoldsteinandTimmers,1982;HuberandViskanta,1994;Olssonetal.,2005;Saripalli,1983).

Jet inletumax = 40 ms–1

Tjet = 298 K

Jetdirection

Potentialcore

Stagnationpoint

Axis Model aluminum cookie

3.94e+01

3.55e+01

3.15e+01

2.76e+01

2.36e+01

1.97e+01

1.58e+01

1.18e+01

7.88e+00

3.94e+00

0.00e+00ms–1

fIgure. Contourplotoftotalvelocityinaturbulentimpingingjetonamodelcookieatz/d=3.(FromNitin,N.andKarwe,M.V.,Journal of Food Science69(2),59–65,2004.WithpermissionfromBlackwellPublishing.)(Seecolorinsertafterp.158.)

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HeattransferduringmultiplejetimpingementisaffectedbytheReynoldsnumber,nozzle-to-platespacing, jet–jetmixing,nozzle-to-nozzlespacing,andnozzlearraygeometry.Arecentstudyshowedthatspacingbetweenthejetsshouldbehighenoughbutnottoohightoattainhighheattransferrate(Olssonetal.,2005).Ifthedistancebetweenthejetsistoosmall,theentrainmentofairbetweenthejetsissuppressedandalmostnorecirculationzoneisobserved,whereasifthedistancebetweenthejetsistoolarge,alargerecirculationzoneiscreatedbetweenthejets,leadingtomorekineticenergylossandlowerrateofheattransfer(Olssonetal.,2005).

350

300

250

200

150

100

50

0

40 ms–1

30 ms–1

20 ms–1

10 ms–1

Radial position on cookie top surface (m)0 0.01 0.02 0.03

Surfa

ce h

eat t

rans

fer c

oeffi

cien

t h (W

m–2

K–1)

350

300

250

200

150

100

50

0

40 ms–1

30 ms–1

20 ms–1

10 ms–1

Radial position on cookie top surface (m)0 0.01 0.02 0.03

Surfa

ce h

eat t

rans

fer c

oeffi

cien

t h (W

m–2

K–1)

(a)

(b)

fIgure. Variationoflocalsurfaceheattransfercoefficientonthetopsurfaceofthemodelcookieasafunctionofpositionandjetvelocityatjettemperatureof450Kfor(a)z/d=2,(b)z/d=5.(FromNitin,N.andKarwe,M.V.,Journal of Food Science69(2),59–65,2004.WithpermissionfromBlackwellPublishing.)(Seecolorinsertafterp.158.)

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Different techniqueshavebeenused to study thefluidflowandheat transferassociated with jet impingement flows. The use of the smoke wire method is aqualitative approach to study the flow pattern of impinging jets in food applica-tions(e.g.,bakingorroastingofhotdogs)(Cornaroetal.,1999;PopielandTrass,1991;Viskanta,1993).Thequantitativeexperimentalmeasurements,likehotwireanemometry(GardonandAkfirat,1965;SugiyamaandUsami,1979)andpitottube(KocerandKarwe,2005;StoyandBen-Haim,1973)whichmeasurepointvelocityof impingingjets,are invasive techniquesandare likely to inducechanges in theflowfield.Ontheotherhand,laserdoppleranemometry(LDA)(Durstetal.,1981;MarcroftandKarwe,1999;Marcroftetal.,1999)andparticleimagingvelocimetry(PIV)(Adrian,1991)arenoninvasivetechniquesthathavebeendevelopedtoquanti-tativelymeasuretheflowfield,althoughthesetechniquesareexpensive.

The lumped capacitance technique has been used to determine average heattransfer coefficient during jet impingement processing (Kocer and Karwe, 2005;Nitin andKarwe,2001).Liquid crystals (Baughn, 1995;Goldstein andTimmers,1982;LeeandLee,2000;Mesbahetal.,1996),two-dimensionalinfraredradiom-eter(Panetal.,1992;PanandWebb,1995),andnaphthalenefilm-indirectapproach(Angiolettietal.,2003;SparrowandLovell,1980)havebeenusedtomeasurethespatialvariationofsurfaceheattransferforamodelobject.

11.2.2 BakinGinJeTimPinGemenTovens

Bakingisaprocesswhereheatandmasstransferoccursimultaneouslywithinthefoodsystem.Heattransfercausestemperaturerise;masstransfercausesmigrationand loss of moisture in the food. This temperature rise, moisture migration, andevaporationcausestarchgelatinization,proteindenaturation,crustformation,colordevelopment, andflavor formation.Theextentof all thesephysical andchemicalchangesdeterminesthefinalproductquality,whichisdefinedbytexture,color,fla-vor,andshelflife.

Duringbaking,whilemoisturemigrates to theproduct surface, it encountersaheavy,cool,moist,andstagnantlayeraroundtheproductsurface,whichactsasan insulatorandgreatlyslowsheat transfer(WalkerandSparman,1989).Naturalconvectionisnotenoughtomovethiscoldlayeraroundtheproductsurface(Henke,1985;WalkerandSparman,1989).Blowingairhorizontallyaroundtheproductsur-facebyforcedconvectiononlydecreasesthiscoldlayer(Henke,1985).Ontheotherhand,impinginghigh-velocityhotairjetsontotheproductsurfaceremovesthiscoldboundary layerand replaces itwithhotteranddrierair.This results in increasedheatandmasstransferrateattheproductsurfacewhichhelpstoachievethedesireduniformbaking(Henke,1985;Walker,1987;WalkerandSparman,1989;WalkerandLi,1993;YinandWalker,1995).

Althoughthemoisturelossrateishigherinjetimpingementovens,thenetmois-ture loss in the products baked in jet impingement ovens is less than that of theonesbakedinconventionalovensduetoshorterbakingtimes(Olssonetal.,2005;WalkerandLi,1993;WalkerandSparman,1989).Therefore,thefoodsbakedinjetimpingementovenshaveabetteryieldandhighermoisturecontent,andtheirshelf

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lifeandtextureareimproved(WalkerandLi,1993;WalkerandSparman,1989;YinandWalker,1995).

Theotherreasonforhighmoistureretentioninproductsbakedinjetimpinge-mentovensisthequickcrustformation.Ahigherrateofsurfacemoistureremovalunderhotair jet impingement results inquickcrust formation.Because thecrusthaslowermoisturediffusivity,theproductretainsmoremoistureinside,whichcanenhancetheperceivedqualityof theprocessedfood(Walker,1987), includinganincreaseinshelflifeaswellasretentionofsomekeyhealth-promotingnutraceuticalcompoundssuchasOmega-3fattyacids(Borquezetal.,1999).Inaddition,greatermoistureretentionresultsinimprovedflavorretention(Henke,1985).

Thecrustandcolorformationarekeyparametersthatidentifytheacceptabilityof thebakedproductsbyconsumers.The formationofcrust and increase in sur-facetemperaturebeyondtheevaporationtemperatureresult incolordevelopment.Browningreactions,mainlycaramelization,havebeenknowntoberesponsibleforthedevelopmentofthecrustcolor,andtheyneedhighertemperatures(>100°C)tooccur.Theairtemperatureisthemostsignificantparameteraffectingthecolordevel-opment(Olssonetal.,2005).Whenbakingatthesametemperature,therateofcolordevelopment in jet impingementovens is faster than thatwithconventionalovensduetofastersurfacetemperaturerise(Olssonetal.,2005;Wahlbyetal.,2000).Thecrust thickness isalsoaffectedbyair temperatureandvelocityandprocess time.Shorterheatingtimeresultsinathinnercrust,whereasthecrustthicknessincreaseswithincreaseinairtemperatures(Olssonetal.,2005).Inaddition,thecentertem-peratureincreasesfasterduringimpingementbaking,leadingtofastersettlingofthecrumb(Wahlbyetal.,2000).

Table11.1showsthecomparisonofbakingtimesandairtemperaturesforprod-ucts baked in conventional versus jet impingement ovens (Walker and Sparman,1989).Itisimportanttonotethatprocessingtimesandtemperaturesmayvarywith

taBle.ComparisonofBakingtimesandairtemperaturesforProductsBakedinConventionalversusjetImpingementovens

Product Conventionaloven jetImpingementoventime(min) airtemperature

(°C)time(min) airtemperature

(°C)Muffins 26 174 12 154

Layercake 26 159 16 149Poundcake 75 134 55 124Croissant 18 171.5 12 154

Puffpastry 22 166.5 13 159Appledanish 20 171.5 10 149

Cherryturnovers 28 171.5 14 154Raisinoatmeal

cookies15 166.5 12 159

Raisinnutoatmealcookies

16 169 12 154

Source:Walker,C.E.andSparman,A.B., AIB Research Department, Technical Bulletin,XI,11,Novem-ber,1989.Withpermission.

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theoventype,productformulation,sampleweight,andpancharacteristics(WalkerandSparman,1989).ThejetimpingementovenusedinthisstudywasaJetSweep®airimpingementovensetwiththeupperjetfingerslocated8cmabovetheproductsurface.Airvelocitywas15m/sat4cmawayfromtheorificeand6to13m/sattheproductsurface.Thestudyshowedthatbothexternalandinternalappearancesofthefinishedfoodsweresimilar(WalkerandSparman,1989);however,thebakingtimewassubstantiallylessinthecaseofjetimpingementovens.

Anotherstudyinvestigatedthebakingofcakesinfivedifferenttypesofovens:an electrically heated convection oven, an electrically heated conveyor-type jetimpingementoven,agas-heatedconveyor-typejetimpingementoven,ajetimpinge-ment oven, and a jet impingement–microwave hybrid oven. Table11.2 shows theprocesstimesandtemperatures,heattransfercoefficients,andtotalenergyrequiredbakinga20-cmlayercakeintheseovens(LiandWalker,1996).Thestudyshowedthat the cakesbaked in jet impingementovenshad slight crumbcompaction andfirmertexturethanthosebakedintheconventionaloven.Itwasalsoobservedthatincreasingbaking time,airvelocity, and temperature resulted in increase inboth

taBle.

ComparisonofProcessParametersforvarioustypesofCommercialovensConventional

oven(electrically

heated)

Conveyor-typejetImpingementoven

jetImpingement

oven

hybridoven(jet

impingementand

microwave)

(electricallyheated)

(direct-firedgas)

Model DespatchMini-Bake(DespatchOvenCo.,

Minneapolis,MN)

Middleby-Marshall

modelPS200T(Middleby-

MarshallInc.,Elgin,IL)

BlodgettMastertherm®

modelMT70PH(BlodgettOvenCo.,

Burlington,VT)

WindshearJetSweep®

(Enersyst,Dallas,TX)

EnersystFoodFinisherIII®(Enersyst,

Dallas,TX)

Optimumbakingtime

30min 18min 18min 14min 6min

Optimumbaking

temperature

177°C 149°C 166°C 149°C 227°C

Apparentconvective

heattransfercoefficient

uppertargetplate

23.3W/m2K 83.8W/m2K 66.4W/m2K 84.8W/m2K 49.1W/m2K

lowertargetplate

17.4W/m2K 110.9W/m2K 91.4W/m2K 105.0W/m2K 98.2W/m2K

Totalenergyrequired

174kJ 158kJ 175kJ 109kJ 144kJ

Source: Li, A. and Walker, C.E., Journal of Food Science 61(1): 188–191, 197, 1996. Withpermission.

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crustcolorandcakefirmness.Thecakesbakedinconveyor-typeovenshadlowervolumesthantheonesbakedinconventionalovens,andtheyshowedstripeswheretheyhadpassedtoocloselybeneaththenozzles.

To summarize, the benefits of air impingement over conventional baking aredecreasedprocessingtime,lowerprocesstemperatures,energyefficiency,uniformheating,andreducedmoistureloss(Henke,1985;Olssonetal.,2005;WalkerandLi,1993).Theproductsbakedinjetimpingementovenshaveimprovedtexture,uni-formlybakedsurface,andinternalstructure(Henke,1985).

Insomebakingapplications,jetimpingementisnotrequiredduringthewholebakingprocess.Instead,differentbakingzoneswithdifferentprocessingtimes,airvelocities, and temperatures are applied to achieve products with desired bakingqualities.Theuseofhighvelocitiesofairatlowtemperaturesduringtheearlystagesofbakinggivesagoodovenspringwithminimumcrustdevelopment.Thispermitsrapidheatmovementtothecenteroftheproduct,whichthenisheldinanintermedi-atezonewherethecrumbstructuredevelops.Finally,theapplicationofhighoventemperatureresultsincrispandbrowncrust(Walker,1987).Ifhightemperatureisappliedtotheproductattheearlystagesofbaking,adry,thickcrustcandevelop.Theformationofathickcrustretardsproperbakingatthecenterbecausethecrustactsasaninsulator(Walker,1987).Differentcombinationsofairtemperature,veloc-ity, andprocessing timescanbeused toachieveacrustwithadesired thickness(WalkerandSparman,1989).Rapidinitialbakingiscriticalinsomeproductswithdense,moistcenters,suchasfruitpies,toachieveabrown,flavorfulcrust,withthedarkening characteristic of dextrinization, caramelization, and theMaillard reac-tions,butoverbakingshouldbeavoidedwhilethecenterheatscompletely(Walker,1987;WalkerandSparman,1989).

. MICroWaveBaKIngteChnologIes

Microwavebakinghastheadvantagesoverconventionalbakingintermsofreduc-tionofbakingtimeandenergy.Variousstudieshavebeenconductedonmicrowavebakingofsoftwheatproducts,andthesestudiesshowedthatconventionalbakingtime was significantly reduced in the presence of microwave heating. Table11.3showsthecomparisonofbakingtimesindifferentovensfordifferentproducts.

The usage of microwave baking in the food industry is limited. In the early1990s, APV Baker (UK) introduced a microwave–conventional baking oven forpostbaking. This oven was developed as an alternative for radio frequency (RF)heating(Bengtsson,2001).Becausemicrowaveequipmentismorecompact,flexible,andconsideredasadvancedtechnology,thereisrecentlyatendencytowardhybridovensinsteadofRFinbakingandpostbakingprocesses.Microwaveovensworkingat896MHzhavebeenreportedinBritainforbreadbakingandproductionofbreadcrumbs(Bengtsson,2001).

11.3.1 PrinCiPlesoFmiCrowaveBakinG

Therearetwomicrowaveheatingmechanismsoffoods:dipolarrotationandionicconduction.Indipolarrotation,polarmoleculesplacedinanalternatingelectricfield

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experiencea rotational force,whichorients them in thedirectionof thefield.Asmoleculestrytorotateinthedirectionofthefield,theycolliderandomlywiththeirneighbors.Asthefieldchangesitsdirection,moleculestrytolineupwiththedirec-tionofthefield,andfurthercollisionstakeplace.Thisresultsinheating.

Ionicconductionisobservedinmaterialscontainingionssuchassalts.Saltiscomposedofpositivesodiumandnegativechlorideionsindissociatedform.Positivechargedparticleswillbeacceleratedtowardthedirectionoftheelectricfield,andnegativechargedparticleswillbeacceleratedinthereversedirection.Anaccelerat-ingparticlecollideswithitsneighborandsetsitsneighborintomoreagitation.Thus,thetemperatureoftheparticleincreases.Thisheatisthentransferredtootherpartsofthefoodbyconduction.

Inmicrowavebaking,heatisgeneratedinsidethefoodbytheenergyequation(Equation11.2):

∂∂= ∇ +

Tt

T QCP

αρ

2

(11.2)

whereTistemperature(K),tistime(s),αisthermaldiffusivity(m2/s),ρisdensity(kg/m3),Cpisspecificheatcapacityofthematerial(J/kg.K),andQistheheatgener-atedperunitvolumeofmaterial(W/m3)whichrepresentstheconversionofelectro-magneticenergy.

TherelationshipbetweenQandelectricfieldintensity(E)atthatlocationcanbederivedfromMaxwell’sequationsofelectromagneticwavesasshownbyMetaxasandMeredith(1983):

Q fE= 2 02Πε ε" (11.3)

taBle.

ComparisonofProcessParametersforMicrowaveandConventionalovensoventypeandBakingCondition

Product Microwaveoven Conventionaloven ref.

Madeiracake 100%power,40s(Fullpower:900W)

200°C,600s Megaheyetal.,2005

Modellayercake 100%power,6min(FullpowerbyIMPI

test:600W)

180°C,25min Sumnuetal.,2000

High-ratiowhitelayercake

100%power,5.5min(Fullpower:650W)

190°C,25min MartinandTsen,1981

Whitelayercake 50%power,4min(FullpowerbyIMPI

test:706W)

175°C,24min Sumnuetal.,2005

Cannedbiscuitdough 50s,100%(Fullpower:900W)

218°C,10min PanandCastell-Perez,1997

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whereε0isthedielectricconstantoffreespace,ε′′isthedielectriclossfactorofthefood, f is the frequencyof theoven,andE is the root-mean-squaredvalueof theelectricfieldintensity.

Afterheatisgeneratedinsidethefood,therestofthefoodisheatedbyconduc-tion. In conventionalbaking, food isheatedbyconduction, convection, and radi-ation. The air inside the microwave oven is not heated as in conventional ovens.Therefore,foodsbakedbymicrowavesarenotheatedbutarecooledbyconvectionatthesurface.

Dielectricpropertiesarethephysicalpropertiesofafoodthataffectmicrowaveheating.Dielectricpropertiesincludethedielectricconstantandthedielectriclossfactoroffoods.Thedielectricconstantandthelossfactorrepresent theabilityofa foodmaterial to store electrical energy andconvert electrical energy intoheat,respectively.Thedielectricpropertiesoffooddependontemperature,moisturecon-tent,saltcontent,andcompositionoftheproduct.Therearelimitedstudiesintheliteratureonthedielectricpropertiesofbakedproducts.

KimandCornillon(2001)studiedtheeffectsofmixingtimeondielectricprop-ertiesofwheatdough.Asmixingtimeincreased,thedielectricconstantandthelossfactorofwheatdoughdecreasedduetoalowamountofmobilewaterinthesampleaftermixing.Theincreaseintemperaturewasshowntoincreasethelossfactorofdoughwhichcouldbeduetotheincreasedamountofdissolvedions.

ThedielectricpropertiesofstarchslurrieshaverecentlybeenstudiedbyMot-wanietal.(2007).Thedielectricconstantofstarchslurrydecreased,butitslossfactor increased with increasing starch concentration. The dielectric constantdecreasedwithincreasingtemperatureforallfrequencies.Thevariationofthelossfactorwithtemperaturewasafunctionoffrequency.Itincreasedwithtemperaturebetween15MHzand450MHzandthendecreasedwithincreaseintemperaturebetweenfrequenciesof450MHzand3GHz.Thedielectricconstantof20%starchslurrywasfoundtobesignificantlycorrelatedwithgelatinization(Motwanietal.,2007).

Thefirststudyonthevariationofdielectricpropertiesofbakedproductsdur-ingmicrowave–infrared(MIR)andmicrowave–jetimpingement(MJET)wasper-formedonbreadbySumnuetal.(2007).Thedielectricpropertiesofbreadswereshown todecrease sharplyduring the initial stagesof baking and then remainedconstant(Figure11.5).Thesharpdecreaseindielectricpropertieswithbakingtimewasexplainedbytheincreaseintheporosityduringbaking.Thedielectricproper-tiesofcrustwereshowntobesignificantlyhigherthanthecrumbportion,becausecrustwaslessporousthanthecrumbportion.

Dielectricconstantandlossfactorofcakesampleswereshowntobedependentonformulation,bakingtime,andtemperature(Sakiyanetal.,2007).Theincreaseinbakingtimeandtemperaturedecreaseddielectricconstantandlossfactorofallformulations.Fatcontentwasshowntoincreasedielectricconstantandlossfactorofcakes.Variationofdielectricpropertiesofcakesduringbakingwasexplainedbyporosityandmoisturecontent.

52748.indb 225 2/6/08 2:27:26 PM



MIR

MJET

0 2 4 6 8

25

20

15

10

5

0

MIR

MJET

0 2 4 6 8

12

10

8

6

2

4

0

Time (min)

Loss

Fac

tor

Die

lect

ric co

nsta

nt

Time (min)

(a)

(b)

fIgure. Transientdielectricconstant(a)andlossfactor(b)ofbreadsmeasuredatthecentral regionof crumbduringbaking indifferent heatingmodes. (MJET:microwave–jetimpingement,MIR:microwave–infrared.)(FromSumnu,G.,Datta,A.K.,Sahin,S.,Keskin,S.O.,andRakesh,V.,Journal of Food Engineering78(4),1382–1387,2007.WithpermissionfromElsevier.)

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11.3.2 qualiTydeFeCTsinmiCrowave-BakedProduCTs

Microwave-bakedsoftwheatproductshavevariousqualityproblemssuchaslowvol-ume,firmortoughtexture,andhighmoistureloss(Sumnu,2001).Thelowvolumeandfirmortoughtexturecanbeexplainedbytheinsufficientstarchgelatinization.Duetotheshorttimeofmicrowaveheating,thereisnotenoughtimeforstarchtocompleteitsgelatinization.Itisassumedthatthespecificinteractionofmicrowavewithglutenisresponsibleforthetoughnessofbakedproducts.Theexactmechanismofinteractionofmicrowaveswithglutenisnotknown.Campanaetal.(1993)showedthatdryingofwheatbymicrowavesdidnotaffecttotalproteincontentbutchangedthefunctionalityofgluten.Rogersetal.(1990)showedthatthemicrowavetoughen-ingeffectwasnottheresultofcross-linkingbydisulfidebondformation.

Another reason for thehard textureofbakedproducts inmicrowaveovens isthehighmoisturelossintheseproducts.Itwasshownbyvariousresearchersthatmicrowave-bakedproductsweredrier thanconventionallybakedones (Keskin etal.,2004;Lambertetal.,1992;Seyhunetal.,2003;Sumnuetal.,1999,2005).Thiscanbeexplainedby thedifference in themechanismsofmicrowaveheatingandconventionalheating.AsexplainedinSection11.3.1,thereisinternalheatgenera-tioninmicrowaveheating.Thiscreatessignificantpressureandconcentrationgra-dients,whichincreasetheflowofmoisturethroughthefoodtotheboundary(Datta,1990).Inaddition,thecrustformedinconventionalproductscannotbeobtainedinmicrowave-bakedproducts.Thus,thereisnocrustonthesurfaceoftheseproductstorestrictmoistureloss.

Crustandsurfacecolorcannotbeformedinmicrowave-bakedproducts.Micro-wavesaregeneratedinsidethefoodsandtheairinsidethemicrowaveovenisnotheated.Therefore, thesurface temperatureof theproductscannot reach tempera-turesnecessaryforMaillardandcaramelizationreactions.Inaddition,themoistureremovedfrommicrowave-bakedproductscondenseswhenitcomesincontactwiththeairatambienttemperatureatthesurface.Becausethemoisturecontentatthesurfaceoftheproductishigh,adrycrustcannotbeformed.

BecauseMaillardandcaramelizationreactionsarenotobservedinmicrowave-bakedproducts,flavorsgeneratedasa resultof these reactionsarealsoabsent intheseproducts,andthearomaprofileofamicrowave-bakedcakeissimilartothatofbatter.WhortonandReineccius (1990) showed that aromas (nutty,brown,andcaramel type) observed in a conventional cake were absent in microwave-bakedcakes.Inaddition,unwantedflavorssuchasflouroregg-likeflavorsdevelopduringthemicrowavebakingofcakes.Itispossibletomasktheseundesiredflavorsandtoobtainasimilarflavorprofilewithconventionallybakedcakesbyaddingflavoringagentstothecakerecipe(SumnuandSahin,2005).

Rapid staling is another problem in microwave-baked cakes. The stal-ing mechanism of microwave-baked cakes is still unclear. High moisture loss inmicrowave-bakedproductswasthoughttobeoneofthereasonsforthestalingofmicrowave-bakedproducts.Itwasshownthatshelflifeofbreadwasincreasedbyincreasingitsmoisturecontentby2%(Stauffer,2000).Ahighamountofamylosethatisleachedduringmicrowavebakingmaybeanotherreasonfortherapidstal-ingofmicrowavereheatedbreads(HigoandNoguchi,1987)andmicrowave-baked

52748.indb 227 2/6/08 2:27:30 PM



cakes(Seyhunetal.,2005). Whenamylosecontentsofmicrowaveandconvention-allybakedcakeswerecomparedjustafterbakingandduringstorage,itwasseenthatmoreamylosewasleachedoutduringmicrowavebakingthanconventionalbak-ing(Figure11.6).

11.3.3 sTarChGelaTinizaTioninmiCrowaveBakinG

Starchisoneofthemaincomponentsofsoftwheatproducts,soitisnecessarytodiscusswhathappenstoastarchgranulewhenitisheatedbymicrowaves.Studyingstarchgelatinizationinamicrowaveovenwillbehelpfultoimprovethequalityofmicrowave-bakedproducts.

GelatinizationofwheatstarchhasbeenstudiedbyGoebeletal.(1984).Inthisstudy,microwave-heatedstarchsampleswerefoundtobenonuniformascomparedtoconventionallyheatedones.Zylemaetal.(1985)showedthatthedistributionofswollengranulesandthedegreeofswellingdependedonheatingmethod(micro-waveorconductionheating).Starchgranulesheatedbyconductionwereswollentothesameextentasthoseheatedbymicrowavesinlimitedwatersystems(1:1and1:2)butwerelessswollenforsystemscontaininghigheramountsofwater.

Sakonidouetal.(2003)showedthatstarchgelatinizationaftermicrowaveheatingwasincompleteascomparedtoconventionalheatingwhenmaizestarchsuspensionsatdifferentconcentrationswereheatedbymicrowaves.Althoughtherequiredtem-peraturewasreachedduringmicrowaveheating,gelatinizationwasnotcompleteduetothelimitedstarch–waterinteractionduringtheshorttimeofmicrowaveheating.

ConventionalMicrowave

0 1 2 3 4 5

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Am

ylos

e (%)

Storage time (day)

fIgure. Variationofamylosecontentofcakesbakedindifferentovens.(FromSey-hun,N.,Sumnu,G.,andSahin,S.,Food and Bioproducts Processing83,1–5,2005.WithpermissionfromInstitutionofChemicalEngineers.)

52748.indb 228 2/6/08 2:27:32 PM



Lewandowiczetal.(2000)showedthatmicrowaveheatingreducedcrystallinity,solubility,andswellingcharacteristicsofwheatandcornstarches.However,micro-waveheatingdidnotaffectthosecharacteristicsofwaxycornstarch.Starchgelati-nizationofmicrowave-treatedsamplesoccurredathighertemperatures.Table11.4shows the gelatinization temperatures and gelatinization enthalpy of native andmicrowave-heated cereal starches. As can be seen in Table11.4, wheat and cornstarcheswerepartiallygelatinizedinthemicrowaveoven.However,gelatinizationofwaxycorninmicrowaveheatingwasfoundtobeinsignificantbecausegelatini-zation enthalpy values of native and microwave-treated samples were almost thesame.

Palav and Seetharaman (2006) investigated whether the starch gelatinizationstepsinthemicrowaveovenweredifferentfromthoseinconventionalheating.Theyfoundthatswellingofstarchgranulesheatedbymicrowavesdidnotoccurpriortothelossofbirefringence.However,instarchgranulesheatedbyconduction,swellingandlossofbirefringenceoccurredsimultaneously.Thelossofcrystallinearrange-ment inmicrowave-heated samplesoccurred at a lower temperature compared tothatobservedforconduction-heatedsamples.Duetotherotationalmotionofpolarmolecules,thecrystallinelamellaofamylopectinwasaffected,crystalarrangementwasdestroyed,andnoswellingoccurred.Granuleswellingwasobservedat tem-peraturesgreaterthan65°Cinmicrowaveheating.Granuleswellingfollowedlossofbirefringence.Thisisincontrasttoconductionheatinginwhichtheswellingofstarchgranulesandmeltingofcrystallitesaresemicooperativeprocesses. Incon-ductionheating,evenat90°C,thestarchgranulemaintainsitsintegrity;however,inmicrowaveheating,granularresidueswereobserved.Thiscouldbeexplainedbytheruptureofgranulesduringmicrowaveheatingwhichisduetothemechanismofdipolarrotation.

11.3.4 miCrowave-BakedCakes

Intheliterature,therearevariousstudiesaboutmicrowave-bakedcakes.Thesestud-iesareaboutimprovingthequalityoftheseproductseitherbyusingdifferentformu-lationsordifferentbakingconditions.

taBle.

differentialscanningCalorimetryvaluesofnativeandMicrowave-heatedCerealstarchesstarchtype native Microwaved

t0(°C) tp(°C) ∆h(j/g) t0(°C) tp(°C) ∆h(j/g)

Wheat 53.6 59.5 11.5 67.4 72.0 3.2

Corn 61.0 69.5 13.8 72.1 76.1 7.3

Waxycorn 60.4 68.6 14.7 66.4 75.1 13.6

Source:ReprintedfromLewandowicz,G.,Janowski,T.,andFornal,J.,Carbohydrate Polymers42(2):2000.WithpermissionfromElsevier.

52748.indb 229 2/6/08 2:27:32 PM



Hydrationlevelhadasignificanteffectonheatingrateofbatterforbothrice-andwheat-starch-formulatedcakes(Sumnuetal.,1999).Asthehydrationlevelincreased,more water molecules became available for the absorption of microwave energy,whichincreasedbattertemperature.Whencakeswereformulatedwithwheat,rice,orcornstarch, itwasobserved thatwheat-starch-containingcakeshad thehighervolumeascomparedtoothers(Sumnuetal.,2000).Thiswasexplainedbythefail-ureofrice-andcorn-starch-containingcakestosettheirstructureduringtheshortmicrowave baking period. The microwave power level was found to be the mosteffective independentvariable in affectingall qualityparameters suchasvolumeandtextureofcakes.

Theeffectsof twodifferentfloursonqualityofmicrowave-bakedcakeswerecompared(Bilgenetal.,2004).FlourAwasstraightgradeflour,andflourBwaswholewheatflour.GlutencontentandmoisturecontentofflourAwerehigherthanflourB.ThebakinglossfromcakesmadewithflourAwasgreaterthanthatofcakesmadefromflourB.ThespecificvolumesofcakesmadefromflourBwerehigherthanflourAandsimilartoconventionallybakedones.Ozmutluetal.(2001)alsoshowedthatmicrowave-bakedbreadswithlowerglutenflourhadhighervolumethantheonesformulatedwithhigherglutenflour. Combiningconventionalheatingwithmicrowaveheatingproducedcakeswithqualitiessimilartothosethatwereconven-tionallybaked(Bilgenetal.,2004).

Cakequalitywasfoundtobeafunctionofconcentrationofmonocalciumphos-phatemonohydrate, which is present in the baking powder. As the concentrationof monocalcium phosphate monohydrate increased, the specific volume of cakesdecreased,andcrumbfirmnessincreased(MartinandTsen,1981).Whencellstruc-turesofmicrowaveandconventionallybakedcellswere investigatedbyscanningelectron microscope, it was found that cell structures of microwave-baked cakeswerecoarserthanthoseofconventionallybakedcakes.Cellsinmicrowave-bakedcakes were irregular and had thicker cell walls than did those in conventionallybakedcakes.

Theeffectsofsucroseadditionincrystallineformorinliquidform(solubilizedinwater)onthequalityofmicrowaveandconventionallybakedcakeswerecom-pared(Bakeretal.,1990a).Itwasfoundthatcakestructureofconventionallybakedcakesshowedmorevariationasafunctionofformulationcomparedtomicrowave-bakedcakes.

Pantypewasfoundtobeasignificantfactorinaffectingtheheatingprofileofmicrowave-bakedcakes(Bakeretal.,1990b).Whencakeswerebakedinglasspans,theedgetemperatureofcakebatterwashigherthanthecentertemperatureduringbaking(Bakeretal.,1990b;Sumnuetal.,1999).Ontheotherhand,theedgetem-peratureofcakebatterbakedinametalpanwaslowerthanthecentertemperatureduringmicrowavebaking(Bakeretal.,1990b).

Therearevariouspatentsaboutmicrowaveablecakeswhichfocusonobtaininghigh-qualitycakesinthemicrowaveoven.AformulationisgivenintheU.S.patentof4,396,635toobtainsoftandmoistcakes(RoudebushandPalumbo,1983).Thecakeformulationcontainsleavening,asugar-to-flourratioof1.4:1to2:1,0to16%shortening,and2to10%emulsifier.Inanotherstudy,spongecakeswerepreparedbyusingmesophasegels,whichroseandformedanacceptablecakewithhighvolume

52748.indb 230 2/6/08 2:27:32 PM



(McPhersonetal.,2002).Mesophasegelisformedwithemulsifiersandanaqueousphase.ItcontainseitheramixtureofhighandmediumemulsifierswithHLBvaluesof11to25and6to10,respectively,oramixtureofhigh,medium,andlowemulsi-fierswithHLBvaluesof11to25,6to10,and2to10,respectively.Mesophasegelisadded5to15%tocakebatter.Thenameoftheemulsifiersthatcanbeusedincakebatterandformulationofthecakebatteraregivenindetailinthepatent.

Seyhunetal.(2005)addeddifferenttypesofstarches(corn,potato,waxycorn,amylomaize,andpregelatinized) tocakeformulations to reducestalingofmicro-wave-baked cakes. The control cake formulation contained no additional starch.Starchesexceptamylomaizesignificantlyreducedfirmnessofcakesascomparedtocontrolcakes.Pregelatinizedstarch,themosteffectivestarchontheretardationofstaling,canberecommendedforcakestobebakedinthemicrowaveoven.Theuseofemulsifiersandgumswasshowntoretardthestalingofmicrowave-bakedcakes(Seyhunetal.,2003).

Characteristics of cake batter during baking were studied by Megahey et al.(2005).Inmicrowavebaking,batterexpandedrapidlyduringtheinitial30to50sec,butduringconventionalbakingitwaswithin420sec.Thiswasfollowedbyaperiodof slight shrinkage of cakes. Cakes baked at 250 W power in a microwave ovenshowedimprovedspringiness,firmness,andmoisturecontentascomparedtocakebakedinaconventionaloven.

11.3.5 miCrowave-BakedCookies

In the baking industry, checking is a failure in cookies, which is due to unevenexpansion or contraction of moisture due to nonuniform distribution of moisturewithintheproduct.Microwavebakingwasfoundtosignificantlyreducecheckingto5%comparedto61%inaconventionallybakedcookie(Ahmadetal.,2001).Within24hafterbaking,biscuitshadanaverageof18%checking,andmicrowavedbiscuitshadanaverageof1%checking.Thisshowedthatmoreuniforminternalmoistureprofilescanbeobtained inmicrowavebaking.Thepostbakingofbiscuitscanbedonebymicrowavestoreducecheckingandtoimproveproductquality(Ahmadetal.,2001).

The rate of weight loss of microwave-baked biscuits was significantly higherthanconventionalbaking(PanandCastell-Perez,1997).Whenfinalbakingincon-ventionalgasandmicrowaveovenswascompared,highermoisturelossandmini-malcolorchangeoccurredinmicrowaveheating(Sosa-Moralesetal.,2004).

. hyBrIdteChnologIes

Because therearequalityproblems inmicrowave-bakedproducts, itwas recentlyrealizedthatmicrowavesshouldbecombinedwithotherheatingmethodsinordertoobtainhigh-qualityproducts.Thesehybridtechnologiesaremicrowave–jetimpinge-mentovensandmicrowave–infraredcombinationovens.

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11.4.1 hyBridJeTimPinGemenTandmiCrowaveovens

Althoughmicrowaveovensprovidemoreuniformheatingoftheinteriorregionsofaproductinashortertime,thelackofcrustformationandsurfacecolordevelop-mentaretheirdrawbacks(WalkerandLi,1993).Intensivemicrowaveheatingcauseshighinternalpressurethatpushesmorewatertotheproductsurfacewhichshouldberemovedbytheadditionofhotairorinfraredheating(Nietal.,1999).Astudyinvestigatingthetemperatureandmoistureprofilesforinfraredandhotairassistedheatingshowedthatforfoodswithlargerinfraredpenetrationdepth,infraredheat-ingcanactuallyincreasethesurfacemoisturethathastoberemovedbyconvectionheatingtoobtaincrust(DattaandNi,2002).Anotherstudyinvestigatingtheeffectofairflowonheatandmasstransferinamicrowaveovenshowedthatconvectionimprovestheheattransferandreducesmoistureaccumulationinsidetheoven(Ver-bovenetal.,2003).

Considering the advantages of air impingement and microwave ovens, rapidmicrowave baking of the interior of the product matches quite well with rapidimpingementbakingwhich leads toquickcrust formationandcolordevelopment(Datta et al., 2005;Walker andLi, 1993;Yin andWalker, 1995).Duringbakinginamicrowaveoven,whenthewatervaporleavestheproduct,itcomesincontactwithcool air at the surface,whichcausescondensationof thevaporat theprod-uctsurfaceandleadstoasoggysurfacetexture.Inaddition,thiscoolambientairinsidethemicrowaveovencausessurfacecooling,andthelowsurfacetemperaturepreventsMaillardreactionsandcaramelizationfromtakingplace.Impinginghigh-velocityhotairtotheproductsurfacereplacesthiscoolstagnantairwithhotanddryair, increases theheat transfer rate,and removes thesurfacemoisture,whichleadstoquickcrustformationandcolordevelopment.Combiningmicrowavewithhigh-velocityimpingementheatingwouldfurtherdecreasetheprocessingtimeandformasurfacecrustrapidly,whichwouldlockthemoistureinsideandthuspreventexcessivedryingoftheproduct.

Browningreactions,mainlycaramelization,havebeenknowntoberesponsibleforthedevelopmentofthecrustcolor,andtheyneedhighertemperatures(>100°C)tooccur.Withonlymicrowaveheating,eventhoughwecouldreducethemoisturecontenttotheequilibriummoisturecontent,thetemperatureatthesurfacecouldnotexceed

JetsMicrowavesource

Conveyor beltor turntable

fIgure. A hybrid jet impingement–microwave oven showing the two modes ofenergytransfer.

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theevaporationtemperatureduetolackofconvectiveheattransferatthesurface,andhence,thebrowningcouldnottakeplace(ShuklaandAnantheswaran,2001).

Aschematicdiagramofahybridjetimpingement–microwaveovenisshowninFigure11.7.Forcookingandbakingpurposes,hybridovenscombiningmicrowaveand impingement (Sharp R90-GC, Thermador JetDirect, Jenn-Air Accellis 5XP,FujimakSuperJet)havebeendeveloped.ThermadorJetDirectwasdesignedforuseinthehome,andFujimakSuperJetwasdesignedforfoodserviceusebyEnersystDevelopmentCenter(Babyak,2000).

Thecombinationofmicrowaveheatingand impingementheatingwasstudied(LiandWalker,1996;OvadiaandWalker,1998;Sumnuetal.,2007;WalkerandLi,1993;YinandWalker,1995).Astudyshowedthatmorecompactcrumbstructure,firmertexture,surfacecracking,andlowvolumewereobservedincakesbakedinhybridjetimpingementandmicrowaveovenscomparedtoconventionalconvectionandjetimpingementovens(LiandWalker,1996).Theshorterbakingtimewasthekeyproblem inhybrid jet impingementandmicrowavebakingdue to incompletefunctioningofleaveningacidsbeforethestructurebegantoset.Incorporatingmoreairintothebatterbyintensecreaminganduseofliquidshortening,replacingtheconventionalbakingpowderwitharapid-actingone,andadjustingwaterandemul-sifiercontentsappeared to reduce thisproblem(LiandWalker,1996).AsshowninTable11.2,higheroperatingtemperatureswereusedduringbakinginhybridjet

taBle.

ProcessParametersforProductsBakedinthreedifferentovensProduct oventype oventemperature

(°C)Bakingtime(min)

Appledanish Conventional 190 12

Impingement 193 5

Hybrid 193 2.5

Puffpastry Conventional 204 20

Impingement 204 12

Hybrid 204 6.5

Chocolatechipcookies Conventional 190 12

Impingement 204 4

Hybrid 204 2

Blueberrymuffin Conventional 204 12

Impingement 204 7

Hybrid 204 3.5

Cornmuffin Conventional 204 14

Impingement 204 7

Hybrid 204 3.8

Source:ModifiedfromWalker,C.E.andLi,A.,AIB Research Department Technical Bulletin,XV,9,September,1993.Withpermission.

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impingement and microwave ovens to provide the desired surface color at muchshorterbakingtimes(LiandWalker,1996).

Another study compared the baking of different products in a conventional,impingement, and hybrid jet impingement and microwave oven (Table11.5). Thestudyshowedthatalthoughthebakingtimewastheshortestinahybridoven,over-allappearanceandqualityoftheproductweresimilarforthethreeovens(WalkerandLi,1993).Inthesamestudy,someformulationadjustmentsweremadeinlayercakesbysubstitutingaveryrapidleaveningacidwiththeconventionaldouble-actingbakingpowdertoachievethedesiredvolumeinthefinishedproduct(WalkerandLi,1993).

It canbevisualized that themoisturedistributionsandcrust thicknessof thefinalproductwoulddependonthepathfollowedbythebakingprocess(Figure11.8).Bystudyingthevariouscombinationsofpowerlevels,airtemperature,andvelocity,anoptimumcombinationcanbefoundtoproduceaparticularproductwithadesiredmoisturecontent,crustthickness,andcolor.

Anumericalstudywasconductedtounderstandtheeffectofsequencingpowerlevels,airtemperature,andvelocityonmoisturedistribution(Kocer,2005).Twodif-ferentcombinationsofmicrowavepowerlevel,airvelocity,andairtemperaturewerestudiedaslistedinTable11.6.Forallprocesses,thetotalprocesstimewaschosenas1200sec,inwhich180secofmicrowaveheatingwasappliedwith50%microwavepower.Incase1,theprocesswasstartedwithonlyimpingementheating,followedbyhybridimpingementandmicrowaveheating,followedbyonlyimpingementheatingattheend.Inthesecondcase,ontheotherhand,theprocesswasstartedwithhybridjetimpingementandmicrowaveheating,followedbyonlyjetimpingementheating.Figure11.9showsthemoistureprofilesafter1200secofbaking.Asseenfromthe

Cookedcrust

moisture

Pathdependent

Cookeddry, soggy surface

no crustraw

Exte

nt o

f jet

impi

ngem

ent

Extent of microwave

fIgure. Theeffectofjetimpingementandmicrowavesequencingduringhybridbak-ing. (FromKocerD.,PhDdissertation,Rutgers,TheStateUniversityofNewJersey,NewBrunswick,2005.)

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figures,theeffectoffocusingmicrowaveenergywasobservedforcase1,butincase2itwasnotobserved.Fromtheseresults,itcanbeseenthatincreasingtheproducttemperatureatthebeginningoftheprocessbyfastmicrowaveheating,followedbyonlyimpingementheatingresultedinthickercrust.Inaddition,thefocusingeffectdrivenbymicrowaveheatingwasprevented.Thestudyshowedthatbysequencingenergymodes,wecanobtainaproductwithadesiredmoistureprofile.Microwaves,withtheirabilitytopenetratedeepwithintheproduct,shouldbeusedinthefirstzones,rapidlyraisingtheinternaltemperaturetoapointjustbelowthegelatinizationofstarch(Walker,1989).

11.4.2 miCrowave–inFraredComBinaTionovens

Amicrowave–halogenlampcombinationovenwasproducedin1999.ItwassoldbythenameofAdvantium®byGeneralElectricCompany(Louisville,KY).Thisovenincludesthreehalogenlampsinadditiontoaclassicalmicrowaveovendesign.Two1500-Whalogenlampsarelocatedatthetop,andone1500-Whalogenlampisatthebottom.Afterthisovenwasintroducedintothemarket,theeffectsofthisovenonthequalityofbakedproductssuchascakes,cookies,andbreadswerestudied(Kes-kinetal.,2004,2005;Sevimlietal.,2005;Sumnuetal.,2005;Turabietal.,2008).

Halogen lamp heating provides near-infrared radiation, and it has lowerpen-etrationdepththantheotherinfraredradiationcategories.Near-infraredradiation

taBle.

Casesusedtoexploretheeffectofsequencingstages Processvariables Case Case

1.Stage Processtime(seconds) 900 180

Airvelocity(m/s) 10 2.5

Heattransfercoefficient(W/m2K)

40 20

Airtemperature(K) 450 450

Microwavepower 0 50

2.Stage Processtime(seconds) 180 1020

Airvelocity(m/s) 2.5 10


20 40

Airtemperature(K) 450 450

Microwavepower 50 0

3.Stage Processtime(seconds) 120 NA

Airvelocity(m/s) 10 NA


40 NA

Airtemperature(K) 450 NA

Microwavepower 0 NA

52748.indb 235 2/6/08 2:27:40 PM



nodes at radial surface

node

s at a

xial

surfa

ceW (kg water/kg dry solids)

C 3

2.5

2

1.5

1

0.5

2 4 6 8 10 12 14 16 18 20 Br = Rr = 0(a)

(b)

20

18

16

14

12

10

8

6

4

2

A

x = 0

Dx = L/2

nodes at radial surface

node

s at a

xial

surfa

ce

W (kg water/kg dry solids)C

3

2.5

2

1.5

1

0.5

2 4 6 8 10 12 14 16 18 20 Br = Rr = 0

20

18

16

14

12

10

8

6

4

2

A

x = 0

Dx = L/2 3.5

fIgure. Moisturecontoursinpotatofor(a)case1,(b)case2.(FromKocer,D.,PhDdissertation.Rutgers,TheStateUniversityofNewJersey,NewBrunswick,2005.)(Seecolorinsertafterp.158.)

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mainly affects the surface of the product. As discussed before, heat is generatedinsidetheproductwhenmicrowavesareused.Itisknownthatamicrowave–halogenlampovenprovidesthebrowningandcrispingadvantagesofnear-infraredheatingwiththetime-savingadvantagesofmicrowaveheating.

InthestudybySevimlietal.(2005),bakingconditionsinthehalogenlamp–microwavecombinationovenwereoptimizedforcakes.Itwasfoundthat5minofbakingat70%upperhalogenlamppower,60%lowerhalogenlamp,and30%micro-wavepowerresultedincakeshavingqualitycomparablewithconventionallybakedcakes.Thefirmnessandweightlossofcakesincreasedasupperhalogenlamppowerincreased.Thelowerhalogenlamppowerwasfoundtobeinsignificantinaffectingvolume,weightloss,andcolorofcakes.Byusingthehalogenlamp–microwavecom-binationoven,theconventionalbakingtimeofcakeswasreducedby79%.

Inthemicrowave–nearinfraredcombinationoven,itwasshownthattheincreaseinupperhalogenlamppowerandbakingtimeincreasedthecolorchange(∆Evalue)ofcakes(Figure11.10)(Sumnuetal.,2005).Thehigherhalogenlamppowermightincreasethesurfacetemperatureofcakes,whichmightaffectthesurfacecolorfor-mation. Itwaspossible toobtaina similarcolorvaluewithconventionallybakedcakesinmicrowave–nearinfraredcombinationbakingat70%halogenlamppowersand50%microwavepowerafter5min.

Keskin et al. (2005) investigated the possibility of using a microwave–near-infraredcombinationovenforthebakingofcookies.Itwaspossibletoobtaincook-ies having similar characteristics as conventional ones when 70% halogen lamp,

80

70

60

50

40

30

Baking time (min)2 3 4 5 6 7

∆E

fIgure.0 Variationofcolorchange(∆Evalue)incakesduringinfrared(IR)–micro-wavecombinationbakingat50%microwavepowerandatdifferent IRpowers ():50%,():70%.(FromSumnu,G.,Sahin,S.,andSevimli,M.,Journal of Food Engineering71,150–155,2005.WithpermissionfromElsevier.)

52748.indb 237 2/6/08 2:27:46 PM



20%microwavepower,and5.5minbakingtimewereused.Theincreaseinhalo-genlampincreasedthehardnessofcookies.Higherspreadratiocanbeobtainedinmicrowave–near-infraredcombinationbakedproducts.Arapidviscoanalyzer(RVA)wasusedtocomparestarchgelatinizationinconventional,microwave,andmicro-wave–near-infraredbakedcookies.AccordingtopeakviscosityresultsobtainedbyRVA, the increase inbaking time reduced thepeakviscosity,meaning thatmorestarch was gelatinized (Figure11.11). Microwave-baked samples had higher peakviscositythanconventionallybakedonesduetoasmallerdegreeofgelatinization.Asnear-infraredpowerandbakingtimeincreased,peakviscosityapproachedthatofconventionallybakedcookies(Figure11.11).

Recently,thepossibilityofusingamicrowave–near-infraredcombinationovenwasstudiedforthebakingofricecakes(Turabietal.,2008).Ricecakescontainingnoglutenarecriticalforpatientswithceliacdisease,becausethesepatientscannotconsume any gluten-containing products. It was possible to produce high-qualitycakesintheovenwhenricecakeswerecombinedwithdifferentgumsandtheemul-sifierPurawave®(Puratos,Belgium).XanthangumandtheemulsifierPurawavewererecommendedtobeusedinricecakestoachievehighvolumeandsofttexture.

. ConClusIons

Jetimpingementovensareauniquetypeofconvectionoveninwhichhigh-velocityjetsofhotairimpingeonafoodproduct.Ithastheadvantagesofahigherrateofsur-faceheattransferandrapidmoistureremoval,whichresultinquickcrustformation

2250

2000

1750

1500

1250

1000

750

500

Conventio

nal

Microwave

60H/30M/5.0 min

60H/30M/5.5 min

60H/30M/6.0 min

80H/30M/5.0 min

80H/30M/5.5 min

80H/30M/6.0 min

Baking condition

Peak

visc

osity

(cp)

fIgure. Peakviscosityvaluesofcookiesbakedindifferentovens.(H:halogenlamppower, M: microwave power.) (Data from Table11.2, Keskin, S.O., Ozturk, S., Sahin, S.,Koksel,H.,andSumnu,G.,European Food Research & Technology,220,546–551,2005.WithpermissionfromSpringerScienceandBusinessMedia.)

52748.indb 238 2/6/08 2:27:47 PM



and color development. Microwave ovens use electromagnetic energy to heat theproductbymolecularabsorptionofenergy,mainlybywaterandsaltmoleculesinthefoodproduct.Microwaveovensprovidefasterprocessingbyacceleratedheattransferandmoisturemigration.Eventhoughbakingoperationinamicrowaveovenrequiresconsiderablylesstimeascomparedtoaconventionalconvectionoven,thelackofcrustanddesirablecolorformationareitsmainlimitation.Becausemicrowaveheat-ingoffersmanyopportunities,researchershavebeeninvestigatingwaystohavetheeaseoffastprocessingwhilemaintainingquality.Changingtheformulation,usingsusceptors,andaddingflavorsaresomeofthewaystoreducequalityproblemsinmicrowavebaking.Othereffortsincludechangingthedesignoftheovens.Finally,theintroductionofhybridtechnologiessuchasmicrowaveandjetimpingement,andmicrowave and near-infrared are promising improvements to overcome the qual-ityproblemsassociatedwithmicrowaveovens.Thesecombinationovensoffertheadvantages of energy efficiency due to a faster rate of heat transfer; energy sav-ingsdue tooperationat lower temperatureand lessprocessing times;andqualityimprovementwithcrustformation,surfacebrowning,andflavordevelopment,andat thesame timeretentionofmoisture inside thebakedproduct.Morestudiesonheatingmechanism,physicochemicalchangesduringbaking,physicalandelectricalpropertiesoftheproducts,productqualityimprovement,andprocessoptimizationareneededtoeffectivelyusethesealternativebakingtechnologies.

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12 Low-Sugar and Low-Fat Sweet Goods

Manuel Gómez

Contents

12.1 Introduction.................................................................................................24612.2 NutritionalProblemsoftheConsumptionofFatsandSugars.................... 247

12.2.1Sugars............................................................................................... 24712.2.1.1SugarandDentalCaries..................................................... 24712.2.1.2SugarandBloodGlucose...................................................24812.2.1.3SugarandDiabetes.............................................................24812.2.1.4SugarandObesity..............................................................24912.2.1.5SugarandCardiovascularDisease.....................................24912.2.1.6SugarandHyperactivity.....................................................249

12.2.2Fats...................................................................................................24912.2.2.1FatsandObesity.................................................................24912.2.2.2FatsandAtherosclerosis.....................................................25012.2.2.3TransFattyAcids...............................................................250

12.3 FunctionsofSugarsandFatsinSweetGoods............................................ 25112.3.1Sugar................................................................................................ 251

12.3.1.1Yeast-RaisedProducts........................................................ 25112.3.1.2Cakes.................................................................................. 25212.3.1.3Cookies............................................................................... 25312.3.1.4FillingsandIcings..............................................................254

12.3.2Fats...................................................................................................25412.3.2.1Yeast-RaisedProducts........................................................25412.3.2.2Cakes.................................................................................. 25512.3.2.3Cookies...............................................................................25612.3.2.4Fillings................................................................................256

12.4 GeneralStrategiesfortheSubstitutionofSugarsandFats......................... 25712.4.1SugarReplacers............................................................................... 257

12.4.1.1Fructose.............................................................................. 25712.4.1.2IntenseSweeteners............................................................. 25812.4.1.3BulkingAgents................................................................... 259

12.4.2FatReplacers.................................................................................... 26212.4.2.1Carbohydrate-BasedFatMimetics..................................... 26212.4.2.2Protein-BasedFatMimetics...............................................26412.4.2.3Fat-BasedReplacers...........................................................264

12.5 SubstitutionofSugarandFatsinCakesandCookies................................26512.5.1SugarSubstitution............................................................................265

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12.5.1.1Cakes..................................................................................26512.5.1.2Cookies...............................................................................266

12.5.2FatSubstitution................................................................................ 26712.5.2.1Cakes.................................................................................. 26712.5.2.2Cookies...............................................................................268

12.6 Conclusions.................................................................................................269References..............................................................................................................269

. IntroduCtIon

There are two seemingly contradictory trends spanning Western societies. Onedietarytrendistheincreasingconsumptionofsugars,fats,andcaloriesrecordedinrecentdecades;acontrastingtrendisthegrowingawarenessshownbyconsumersofanythingrelatedtopersonalphysicalappearance,fitness,andhealthissues.Ofthetoptenmortalityratesintherankingofleadingcausesofdeath,fivearedietrelated(heartdisease,cancer,stroke,diabetes,andatherosclerosis).Asaresult,andthanksalsotothedietaryrecommendationsmadebyhealth-careprofessionalsandmuchinformationpresentedbythemedia—albeitnotalwaysreliable—amarkedincreaseintheconsumptionoflow-calorie,low-fat,andsugar-freeproductshastakenplace(Figure12.1).Cakes,cookies,andanumberofyeast-raisedbakeryproductsaccountforasubstantialproportionofthefatandsugarintake.Hence,thedevelopmentofspecialdietaryfoods(low-calorie,low-fat,andsugar-freefoods)withgoodorgano-lepticpropertiesshouldenablemanufacturerstodiversifytheirproductionandmakeinroadsintoanemergentsectorofthemarket.Developmentofsuchspecialproductscanhelpimplementandmaintainspecificdiets,particularlyifavailabletoconsum-erswheneatingoutawayfromhome(Sigman-Grant,1997).

Althoughforthiskindofproductareductionincaloriescanbeobtainedbysub-stitutingfibers,orrawmaterialsrichinfiber,forflour(KaackandPedersen,2005),most low-calorie baked goods are produced by lowering fat and sugar contents.Productsrichinsugarsandfatsareusuallyplacedontheupperlevelsofthefoodpyramid,andhencetheinformedadviceisthattheyshouldbeeatensparingly.How-ever,thechallengeofdevelopingspecialdietaryproductsfirstrequiresthesiftingoftruthfrommythbothontheadverseeffectsoftheconsumptionoffatsandsugars,andonthevirtuesofafat-andsugar-freediet.Infact,consumersoflow-fatproductsshowreducedintakesoftotalfat,saturatedfats,andcholesterol,buttheirdietsmayincludeinsufficientamountsofsomeothernutrients(Petersonetal.,1999).

Productsrichinfatsandsugarsareusuallyassociatedwithpleasantsensations,andtheyarehighlyregardedorganoleptically;itisthereforenomeantasktomatchtheirsensorypropertiesandtheirwidespreadacceptability.Tobesuccessfulinthesubstitutionoffatsandsugars,thefoodindustrymustresorttofatandsugarreplac-erscapableofmimickingtheirroles,butthesereplacersseldomperformallthefunc-tionsattributabletofatsandsugars,andconsequently,thenewproductsareboundtoleadtolessfavorablesensoryevaluationresults.Thedevelopmentofspecialdietaryproducts thus demands a thorough understanding of the roles played by fats andsugarsineachformulationaswellasadetailedknowledgeoftheoptionsavailableaspotentialreplacers.Byandlarge,consumersfindtheseproductsnotaspleasantas

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Low-Sugar and Low-Fat Sweet Goods

theregularproducts,althoughtheyreadilyadmittheyare“betterforyou”(Tuorilaetal.,1997).Whencomparedwiththeregularproducts,thepurchaseintentofthesespecialdietaryproductsishigherthanthe“overalldegreeofliking”(Guinard,etal.,1996).Thechallengethatthebakeryindustryfacesisthedevelopmentofmodifiedproductscapableofreceivinghighhedonicratings.Furthermore,inmanycases,themodifiedproductisrequiredtobeassimilaraspossibletotheregularproductitistryingtoreplace.

. nutrItIonalProBleMsofthe ConsuMPtIonoffatsandsugars

12.2.1 suGars

... sugaranddentalCaries

Ithasbeenshownthattheconsumptionofsugar-richfoodspromotesthedevelop-mentofdentalcaries(MakinenandIsokangas,1988;Sreebny,1982).Dentalcariesisacomplexprocessoccurring,inpart,throughtheactionofmicroorganismscapableoffermentingcertaincarbohydratesinthemouth.Theendproductsofthisfermen-tationprocessarelacticacidandsomepolysaccharidesthatadheretothesurfaceoftheteethandformplaques.Thisprocessoftenleadstocavitationoftheteeth.Sugarsarecarbohydratessusceptibletofermentationbymicroorganismsinthemouth,andalthoughthisisnottheonlyfactorresponsiblefortoothdecay,thereisnodoubtitiscloselyinvolvedinitsdevelopment.Itisalsoknownthattherearesomeotherfactorsaffectingtheincidenceofdentalcaries,suchastoothstructure,mouthmicrofloraofeachindividual,properoralhygienehabits,andtheinclusionoffluorineindrinkingwater.Infact,overthelastfewyears,amarkedreductionintheincidenceofdentalcarieshasbeenrecordedinadvancedsocietiesowingtobetteroralhygienepracticesandthefluoridationofdrinkingwater.

fIgure. Consumer consumption of low-calorie, sugar-free foods and bever-ages in the United States. (From Calorie Control Council, Trends and Statistics, 2006,www.caloriecontrol.org/lcchart.html.

1984 1989 1993 1996 2000 2004Year

0

50

100

150

200

Mill

ions

of A

mer

ican

adul

ts

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www.caloriecontrol.org


... sugarandBloodglucose

Thetermglycemicindexhascometoberegardedasimportantinthedetermina-tionofplasmaglucoselevels.Thistermreferstotherelationshipbetweenglucoseabsorptionandaparticularfooditem.Ahighglycemicindexmeansarapidabsorp-tionof carbohydrates,whereasa lowglycemic indexmeansa slowabsorptionofcarbohydrates.However,glucoseabsorptionalsodependsuponthephysicalstateofthefoodstuff,theforminwhichitiseaten,andtheindividualinquestion.Thegly-cemicindexoffoodstuffsisdeterminedthroughpersonaltestsandcomplexproce-dures,neverthelessitisquiteusefulforthediabeticwhoseparamountconcernmustbetoavoidbloodglucoseincreases.Althoughsomeresearchershavequestioneditsusefulnessintheplanningofdiets,therearesignstheglycemicindexisbecomingavaluableconceptinthedevelopmentofspecialdiets.

Overall,sugarsarerapidlyabsorbedinthegut,producingasharpriseinbloodglucoselevels,andthusrapidlyincreasinginsulinsecretiontoallowcellstheuseofthisglucoseandstimulatethesynthesisoftriglycerides.Afterthisstage,adeclineinthebloodglucoseleveloccurs,andhungerarises.Hence,intakeofsimplecarbohy-dratesproducestransitorysatiety.Conversely,complexcarbohydratesareabsorbedmuchmoreslowly,resultinginalowerincreaseofbloodglucoseandthusinasmallersecretionofinsulin.Triglyceridesynthesisisminimal,bloodglucoselevelsaremain-tainedoverlongerperiodsoftime,andhungerarisesmuchmoregradually.

... sugaranddiabetes

Diabetes mellitus is a disease characterized by hyperglycemia because of distur-bancesinthenormalinsulinproductionmechanismortheinabilityofthesecretedinsulin toadequatelyperformits function.Asa result,high levelsofbloodsugarensue,andshockorevendeathmightoccur.Therearetwomaincategoriesofthedisease.Thefirstiscalledinsulin-dependentdiabetes,ortypeIdiabetes;itisusuallyknownasjuvenilediabetesbecauseitsonsettakesplaceatanearlyage.Patientswiththisconditionrequireaninjectionofinsulindaily.ThesecondistypeIIdiabetesornoninsulin-dependentdiabetes,alsoknownasmaturity-onsetdiabetes;itmanifestsitselfamongadultsandseemstobeinfluencedbyageneticcomponent.Inthislattercase,patientsshowsignificantamountsofinsulinintheirplasma;theirdietmustbecarefullycontrolled,andtheymustexerciseregularly.IthasbeenreportedthattheincidenceoftypeIIdiabetesishigheramongobeseindividuals.

Thesepatientsmustreducetheintakeoffoodstuffswithahighglycemicindexandcombinethemwithsomelow-indexfoodstuffs.Fructoseistheonlysugarwithametabolismindependentfromthepresenceofinsulin,henceitsverylowglycemicindexanditswidespreaduseasglucoseandsucrosesubstituteinthemanufactureofproducts aimedatdiabetics.Overall, there isnoclear evidence that a correla-tionexistsbetweensugarconsumptionanddiabetes.On thecontrary, ithasbeenreportedthatdietsrichincarbohydratesreducetheriskofdevelopingdiabetes(Fes-kensandKromhout,1990;Marshalletal.,1994).Nevertheless,someotherauthorshavepointedoutthatdietswithahighglycemicindexthatarelowinfiberincreasetheriskofdevelopingtypeIIdiabetes(Salmeronetal.,1997a,1997b).

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... sugarandobesity

Althoughthebeliefthatadietrichinsugarspromotesobesityiswidelyheld,thereisinfactnoevidencetosupportit.Sugars, likeothercarbohydrates,andproteinsyield4kcal/g,fatsyield9kcal/g,andalcoholyields7kcal/g.Thehumanbodyiscapableofgainingweightwhenmorecaloriesarebeingconsumedthanarerequired.Consequently,sugardoesnotpromoteobesity toagreaterextent thanproteinsorothercarbohydratesdo,andiswellbelowfatsandalcoholincalorieyield(HillandPrentice, 1995). It has been reported, however, that low-sugar diets can result inweightreduction(Colditzetal.,1990),inallprobabilitybecauseoftheirlowercalo-riecontent;someresearchershavesuggestedthatobeseindividualsshowamarkedpreferenceforsugar-richfoods(Drewnowskietal.,1991).Itmayverywellbethatallthisevidencehashelpedkeepalivethenotionthatsugarconsumptionresultsinweightgain.

... sugarandCardiovasculardisease

Studiesonthelinkbetweensugarconsumptionandthedevelopmentofcardiovascu-lardiseasesshowconflictingresults(HowardandWylie-Rosett,2002).YudkinandEvans(1972)andYudkin(1978)assertedthatanexcessiveconsumptionofsugarsiscorrelatedwithcardiovasculardisease,butlaterresearchershavebeggedtodifferfromthatview(Bolton-SmithandWoodward,1994;García-Palmierietal.,1980).Amorerecentstudyhasagainrestatedthevalidityofthelinkbetweenconsumptionoffoodswithahighglycemicindexandcardiovasculardiseaseinwomen(Liuetal.,2000).Atpresent,thereisnoconclusiveevidenceonthispoint,anditistobehopedthatfurtherresearchwillprovidenewclarifyingdata.

Inaddition,severalstudiesabouttheinfluenceofsugaroncholesterolandtri-glycerideshavebeencarriedout.Thus, ithasbeenshownthatadietwithahighsucrosecontentincreasestriglyceridelevels,althoughthiseffectdependsuponthesugarlevelandtherestoftheintakenutrients(FraynandKingman,1995).Similarly,itseemsequallyestablishedthatwhensugarconsumptionisontherise,thereisadropinthelevelofhigh-densitylipoprotein(HDL)cholesterol(Archeretal.,1998).

... sugarandhyperactivity

Itisaquitecommonlyheldbeliefthatsugarconsumptionleadstohyperactivityinchil-dren.However,Wolraichetal.(1985)establishedthatadecreaseinthesugarlevelsinthedietofhyperactivechildrenfailedtoshowanyeffectonthedegreeofhyperactivity.

12.2.2 FaTs

... fatsandobesity

Anexcessofdietary fatentailsahighcaloricdensityofmanyof thecomponentfoodstuffswhich, in turn,causes theexcess fat tobedepositedasadipose tissue,eventuallyleadingtoobesity.Whentheleveloffatistoohighbutthecaloricintakeisadequate,thedrawbackoftenisthelackofessentialnutrientsduetoarestrictedintakeofproducts,suchascerealsandlegumes,richincarbohydratesandproteins.

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For further informationon the relationshipbetween fatconsumptionandobesity,thereareusefulreviewsbyBrayandPopkin(1998)andBrayetal.(2004).

... fatsandatherosclerosis

Anotherparameterassociatedwithfatintakeworthmentioningisthebloodcholes-terollevel(cholesterolemia).Infact,ahighbloodcholesterollevel(hypercholester-olemia)isconsideredtobethefirstfactorofriskforcardiovasculardisease.Ithasbeenestablishedthatserumcholesterolriseswithhighfatintakeeitherbecausetherateofsaturatedfatsisexcessiveorbecausethedailyfatintakeexceeds300mg/day.Fortheirtransportinthebloodstream,lipidsmustbeboundtoproteins,thusforminglipoproteins.Lipoproteinsareclassifiedaccordingtotheirdensityandarecommonlydividedintotwogroups:low-densitylipoproteins(LDL)andhigh-densitylipopro-teins(HDL).LDLcarryendogenouscholesteroltowardthecellswhichcaptureanduseitthroughtheirmembranereceptors.Whenthisreceptionislimitedorthecho-lestrollevelistoohigh,thelevelofLDLinthebloodrises;thisisoneofthemostsig-nificantriskfactorsforatherosclerosis.Ontheotherhand,HDLtransportcholesterolusedupbythecellstowardthelivertobedisposedofasbileacids.AnincreaseinHDLlevelsinthebloodmeansanimprovedprotectionagainstatherosclerosis.

Polyunsaturated fatty acids (seed and fish oils) lower blood cholesterol levelsbut do not help raise the HDL levels. Alternatively, monounsaturated fatty acids(olive oil) do not modify blood cholesterol levels but raise HDL levels and havethenapositiveeffect.Asarule,areducedintakeofsaturatedfattyacidsnotover10%ofdailycalorieintakeisrecommended.Therecommendedratiointhefattyacidintakeis1/1/1(saturated/monounsaturated/polyunsaturated),keepinginmindthatthereshouldbeanadequateintakeofessentialfattyacids(nomorethan1%ofkilocaloriesconsumed).Outstandingreviewsabouttheeffectofdifferentfattyacidsoncholesterollevelsandatherosclerosisareavailable(KhoslaandSundram,1996;Kritchevsky,2000).

Fatintakehasalsobeenconnectedwithagreaterriskofdevelopingcoronaryconditionsandcolonandlungcancer,butstudiesdisagree,anditcanbesafelystatedthatnocurrentconsensusexistsonthesepoints.Rothstein(2006)recentlypublishedahistoricaloverviewdealingwiththesestudies.

... transfattyacids

Afinalfactortobeconsideredwhendiscussingfatintakeisthepresenceoftransfattyacidsinthediet.Itisknownthatintakeofthiskindoffattyacidsincreasesfatcholes-terollevelsandthoseofLDLcholesterol,whereastheHDLcholesterollevelislow-eredwiththecorrespondingriskofcloggedarteries(Ascherio,2006;AscherioandWillett,1997;Katanetal.,1995;Lichtenstein,2000).Moreover,intakeoftransfattyacidshasbeenassociatedwithagreaterriskofdevelopingtypeIIdiabetes,althoughtheevidenceprovidedissomewhatcontradictory(OdegaardandPereira,2006).

Inconclusion, in theircontinuingeffort todevelopproductswithbetternutri-tional characteristics, manufacturers of bakery products should not just focus onproducinglow-calorieproducts,but,inaddition,theyshouldmeetthechallengeofnutritionallyimprovingthefatstheyuse.

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. funCtIonsofsugarsandfatsInsWeetgoods

12.3.1 suGar

Notallbakeryproductsrequireaddedsugar,butthecommonpracticewithmostoftheseproducts is to includesugar in theirformulations.Amountsrangefromlessthan5%insomebreadstoover25%incertaincakes.High-ratiocakescontainmoresugarthanflour,andtheeffectofthesugarcontentontheirprocessingandqualityisobvious.Traditionally,sucrosehasbeenthesweetenerofchoice,thoughbakershaveavailabletothemawiderangeofsugarsderivedfromthehydrolysisofcerealstarch,suchasglucoseandfructosesyrups.

Insomefoods,sugarisjustasweeteningagent.Thesubstitutionstrategymustthenrelyontheuseofintensesweetenerssuchassaccharinandaspartame.How-ever,inbakeryproducts,thefunctionsofsugararemuchmorecomplexandvarydependingondifferenttypesofproducts.Apartfromitssweeteningaction,sugarperformsavarietyoffunctions,includingfermentationsubstrate,formationofcrustcolor, flavor enhancer, texture modifier, development of structure, and shelf-lifeimprovement.Sugarreplacementissurelyadauntingtaskbecausesometimesnotonlymustingredientsbereplaced,buteventheprocessesinvolvedmustbechangedorreplaced.Thefunctionsofsugarsinbakeryproductshavebeendealtwithexten-sivelyintheliterature(Alexander,1998;Ponte,1990;Sluimer,2005),andadetailedunderstandingofthesefunctionsisanecessaryprerequisitetoadoptingsuccessfulsubstitutionstrategies.

... yeast-raisedProducts

Inleaveneddoughs,yeaststransformsugarsintoalcoholandcarbondioxide.Ifsug-ars are not included in the dough formula, yeasts will mainly transform maltoseresulting from the enzyme hydrolysis of starch. When small amounts of sucrose(1to2%)areadded,yeastswillfirsttransformthissugarbeforeaffectingmaltose,andaslightincreaseintherateoffermentation,particularlyintheearlystages,willtakeplace.When theamountofaddedsugarexceeds5%,a fall inwateractivityanda rise inosmoticpressureoccur indoughs.Thisbrings about a reduction inyeastactivityandfermentationrates.Undersuchconditions,itwillbenecessarytoextendfermentationtimesorraiseyeastdoses.Anotheroptionmightbetheuseofosmotolerantyeasts.

Duringbaking,doughsugarsareinvolvedintwobrowningreactionsthatdeter-minethefinalcolorofthefinishedproduct:Maillardandcaramelizationreactions.The Maillard reaction occurs through interactions between reducing sugars andaminoacidsorpeptides in thedoughwhichresults inmelanoidinformation.Theresultingfinalcolorandaromawilldependuponthetypeofsugarsandaminoacidspresentinthedough.Ontheotherhand,thecaramelizationreactionconsistsofathermaldegradationof sugars that changecolor fromapaleyellow in the initialstagestoadarkbrowninthefinalstagesoftheprocess.Asarule,productswithhighlevelsofaddedsugararebakedatlowertemperaturestopreventtheadverseeffectsanexcessivecaramelizationcouldbringabout.Maillardandcaramelization

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reactionsrequirehightemperatures,over100°C,andthustheycanonlytakeplaceonthecrustofbakedproductsorontoastedbread.

BothMaillardandcaramelizationreactions,togetherwiththefermentationpro-cess,aredeterminantfactorsinthefinalflavorofbakeryproducts.Thus,caramel-izedsugarsimpartanappealingcaramel-likeflavorintheinitialstagesorastrongbitter flavor and burnt aroma in more advanced stages. The type of sugar in thedoughalsoaffectsthecompoundsgeneratedbytheMaillardreactionandthusthearomaoftheproduct.

Indoughswhereglutendevelopmentisessentialduringkneading,sugarscom-petewithproteinsforfreewater,andglutendevelopmentisdelayed.Kneadingtimesshouldthenbeextended.Thepresenceofsugarshasarelaxationeffectondoughs,becausetheirresistanceandconsistencyarereduced.Hence,doughsincludingsugarintheirformulationrequirestrongerflours.Itisalsocommontoreducetheamountofwateraddedtothesetypesofdoughstoimprovetheirconsistency.Forotherprod-ucts, suchascakesandsomecookies,glutendevelopment is supposed tobepre-vented,andthepresenceofsugarscanonlybebeneficial.

An additional effect of sugar is its influence on the starch swelling pattern indoughs.Whensignificantamountsofsugarareinvolved,asinthecaseofsweetgoods,thegelatinizationtemperatureofstarchisraised;thegreatertheamountofsugarinthedough,thehigherthegelatinizationtemperature.Asaresult,thedoughsetsdur-ing baking, a fraction later allowing longer dough expansion times and providingproductsofgreatervolume.Thiseffectisparticularlyimportantwhenbakingcakes.

The water holding capacity of sugars favors a soft and tender crumb. It alsoinhibitsstalingand thegrowthofmicroorganisms,and improves theshelf lifeofbakeryproducts.

... Cakes

Thepresenceofsugarincakesnotonlyinfluencestheirflavor,color,texture,andshelflifebutalsoexertsasignificantinfluenceonthefinalvolumeoftheproduct.Cakemanufacturestartswithbatterpreparationormixofingredients.Atthisstage,theaimistotrapairinthemixintheformoftinybubbles.Duringsubsequentbak-ing,gasfrombakingpowderandthewatervaporreleasedfillthebubblestocreatethefinalporousstructure.Oncelargenumbersofminutebubblesareentrappedinthebatter,thefinalgrainofthecakecrumbcanbefineanduniform.However,iftheentrappedaireventuallyformslargerbubbles,thefinalgrainwillhavelargeandirregularpores.Inadditiontoacorrectaeration,thebattermustreachanappropri-ateviscosity,becauseabatterwithlowviscositywouldresultintheescapeoftheentrappedgases.Astemperaturerisesintheoven,theviscosityofthebatterfallsuntilthegelatinizationofthestarchintheflouristriggeredandasignificantamountof water is absorbed. At this point, viscosity increases until the gelatinization iscompletedandthestructureofthecakeisset,therebyarrestingtheexpansionofthebatter.Gasproductionshouldmainlyoccurthroughoutthegelatinizationprocess,because it is then, prior to cake setting, the capabilityof retaininggas is higher.In thefinalanalysis, itcanbesaid thatsugarplaysa triplerole in theproductionofcakesasitpromotestheentrapmentofairinthebatter,increasesviscosity,and

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delaysthetemperatureofstarchgelatinization(BeanandYamazaki,1978;NgoandTaranto,1986),allofwhichwillcontributetothefinalvolumeoftheproductinadecisivemanner.

Broadlyspeaking,cakesfallintotwomajorgroups.Thefirstgroupincludesallthosecakeswithsubstantialamountsof shortening in their formulations, suchasyellowlayercakes,whitelayercakes,orpoundcakes.Theycanbetermedshorten-ingcakesbecauseshorteningplaysafundamentalrole in theincorporationofairintothebatter.Thesecondgroupismadeupofcakes,suchasspongecakesorangelfoodcakes,with formulations lacking shortening.Cakesbelonging to the secondgroupareusuallyknownasfoam-typecakes,andtheincorporationofairintothesebattersiscloselyrelatedtothefoamingpropertiesofeggwhite.

Severalmethodscanbefollowedinthepreparationofcakebattersorthemix-ingofingredients.Withshorteningcakes,themostcommonapproachisknownasthecreamingmethod,inwhichtheprocessisstartedbybeatingtheshorteningandsugar.In this initialstep,sugarhelpscreamair intothefatbyformingnumerousminutebubbles.Therestoftheingredientsareaddedinsuccessivesteps.Onceintheoven,shorteningmelts,andthebubblesundergoanaqueousphaseexpandingbecauseofthecarbondioxidefrombakingpowder.Thesecakesarecharacterizedbyaveryfineanduniformgrain.Asecondapproachinthepreparationofshorten-ingcakebattersistheone-stagemethodinwhichallingredientsareaddedatonce.Theuseofemulsifyingagentspermitsdirectincorporationandstabilizationofairbubbles in the batter. With both methods, sugar is the determining factor in theincorporationofair,sothatifsugarisremovedfromtheformulation,cakevolumeswillbedrasticallyreduced.

Withfoam-typecakes,eggandsugararewhippeduntilastablefoamisobtained.Someformulations includeonlyeggwhites,butoccasionally,whitesandyolksarewhippedseparately.Infoam-typecakes,sugarhasanessentialfunctionasawhippingaid.Afterthefoamisformed,flourisgentlyfoldedinwithoutbreakingthestructure.

... Cookies

Themarketoffersconsumersavastarrayofcookiesdifferingbothintheirformula-tionsandprocessingmethods.Thesearesomeofthemajortypes:depositcookies,wire-cutcookies,orrotary-moldedcookies.Foreachtype, therewillbedifferentrequirementsasfarastheconsistencyandtextureofcookiedoughsareconcerned.Theeffectofsugaronthesecharacteristicsmustbestudied.Likecakes,mostcook-iesarechemicallyleavenedandhavehighsugarandshorteningcontentsbutaratherlowwatercontent.Formostcookies,theinitialstepconsistsofacreamingprocessinwhichsugarplaysacentralroleintheincorporationofair.Aswasthecaseincakes,sugarshaveasignificanteffectonthefinalstructureofcookiesbydelayingthegelatinizationtemperatureofstarch.Furthermore,theyserveassweeteningandbrowningagentsthroughMaillardandcaramelizationreactions.

Doughconsistencytendstoberegardedasaveryimportantproperty,particu-larlywhenprocessingcookiesatan industrial scale.Depositcookiedoughsmustretainenoughfluiditytomakedepositingfeasible;wire-cutcookiedoughsmustbeproperlyextruded.Inaddition,doughsofrotary-moldedcookiesmustbefirmwhen

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entering the mold and cohesive enough to keep their shape once they have beenreleasedfromthemold.Achievingallthesedifferentlevelsofconsistencydependsonthetypesandamountsofsugarsandshorteningsinvolved.

During oven baking, doughs undergo a rise in temperature which, in turn,resultsinthemeltingoftheshorteningandthegranularsweeteners.Asaresultofthesechanges,waterisliberated,leadingeventuallytoamorefluiddoughandanimprovedcookie spreading.Spreading is also affectedby thegas released in theprocess,anditisconsideredanimportantqualityparameterincookies.Theamountand typeofsweetenerused,aswellasother ingredients,suchasshorteningsandeggs,determinethefinalcookiespread.Afterdoughcooling,sucroserecrystallizesandhardens,helpingtocreatethecharacteristicfracturabilityorsnapofcookies.Ifachewierandsoftertextureissought,differentsweetenersandingredientscapableofminimizingsucroserecrystallizationmustbeintroduced.

... fillingsandIcings

Thefinalstageintheprocessingofmanysweetbakeryproductsistheadditionofsome kind of filling or icing. Most fillings are prepared by whipping shorteningand sugar into a creamy consistency. Fillings are composed of other ingredientsthat provide color,flavor, or consistency.Apart from its sweeteningpower, sugarprovidesbulkandstructure,creatingaerationnucleiwhenshorteningsarewhipped.Sugargranulometryisalsoimportant;coarsegranulatedsugarwillyieldagrainyandsandytexture.Finecrystalsarepreferableforasmoothandcreamytexture.Asforicings,thetypeofsugarusedwilldeterminethedegreeofrecrystallizationaftercoolingandsowhetherthefinalproductshowsamatteorglossyappearance.

12.3.2 FaTs

Theconcentrationoffatsoroilsinbakeryproductsrangeswidely.Insomebreads,fatisabsentfromtheirformulation;inothers,fatispresentatpercentagesbelow5to6%(flourbasis);finally,brioche-likedoughsmayhavefatpercentageswellover50%.Similarly,insomecakes(foamtype),nofatsareadded,butinothers,percent-agesmayrangebetween40and60%(flourbasis),andfatsplayanessentialrole.Inaddition,incookieproduction,fatpercentagesmayrangebetween10and55%.Asmentionedaboveinthecaseofsugars,thefunctionsoffatsinbakeryproductsareverycomplexandvarydependingonthetypeoffatutilized,theamountadded,andtheproductbeingproduced.Severalstudieshavedealtwiththispointindetail(Pyler,1988;Sluimer,2005;Stauffer,1996).

... yeast-raisedProducts

The inclusionofsmallamountsof fat inbreaddoughshasasignificanteffectontheirprocessingandonthequalityofthefinishedproduct.Suchdoughsaremoreextensible, and theirmachinability ismarkedly improved.Afterproofing,doughswithshorteningaremorestableandresistanttopossibleshockswhenthepiecesaretransferred fromtheproofer to theoven. Increasedoven-spring isalsonoticeableduringthebakingofsuchdoughs,becauseshorteningbringsaboutadelayinthe

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reactions marking the end of dough expansion, gelatinization of starch granules,andglutendenaturation.Thefinalproductexhibits largervolumeandcrumbofafinergrain.Fatstrengthensthesidewallsofbreadandminimizesthepossibilityofkeyholing in thefinalproduct.Suchbreadshave softer texture, less crumbliness,andgreatermoistmouthfeel.Thecombinationofalltheseeffectsisknownaslardeffect;itoccursmainlywithsolidfats,providedtheyareevenlydispersedthrough-outthedough,suggestingthatthepresenceofsaturatedfattyacidsisimportant.Alltheseeffectsarealreadynoticeablewithshorteningpercentagesof1%,but ithasbeenestablishedthatmaximumvolumeisobtainedwith5to6%ofshortening.Inanycase,volumeincreasechangeswithdifferentproofingprocedures.Thus,longproofingperiodsgivevolumeincreasesofupto10%,whereasshortproofingperiodsmayyieldincreasesofupto25%.

Withformulationscontaininggreateramountsoffat,asthoseofsomebunsandrollsorofbriochedoughs,otherfactorsmustbetakenintoaccount.Forexample,whenprocessingthesekindsofdoughs,theamountofwatershouldbereducedandkneadingtimesextended.Doughswithhigherpercentagesofshorteningmayrequirethatkneadingbecarriedoutinseveralsteps.Doughconsistencywillbereducedanddoughstickinesswillincrease.Tominimizetheseeffects,inadditiontoreducingtheamountofwaterintheformulation,thefinalkneadingtemperaturemaybeloweredandstrongerfloursmaybeused.Floursofhigherstrengtharerequiredtoattainthecorrectgasholdingcapacity.Thereislessoven-springinthesedoughs,andocca-sionally,theymaycollapseduringorafterbaking.

Inaddition to theeffectsmentioned, all leaveneddoughscontaining shorten-ing show an antistaling effect. Staling increases the firmness of bread crumb asa result of a very slow process, lasting several days, during which the recrystal-lization of amylopectin occurs. When small amounts of shortening are included,loafacceptabilitymaybeextendedbyoneortwodays,whilewithgreateramountsofshortening,loafshelflifecanbeprolongedforweeks.Fattyacidchainsformacomplexwithstarchmoleculeshinderingamylopectinrecrystallizationanddelayingcrumbstaling.Thiseffectissimilartothatobservedwhencertainemulsifierssuchasmonoglyceridesofsaturatedfattyacidsareadded.

Finally,fatshavealubricatingeffect,makingthebakedproducteasytoswallowwithoutadheringtothesurfacesofthemouth.Theyalsohelptoproducebreadthatcanbecleanlyandevenlysliced.

... Cakes

Fats play an essential role in the processing of shortening cakes, including layercakesorsimilarproducts,suchasmuffinsorcakedoughnuts.Fatsareresponsibleforairincorporationintheformofmanysmallbubblesforafineanduniformgraininthefinalproduct.Whentheshorteningpercentageonaflourbasisisincorrectorthewrongkindofshorteningisused,airwillbeentrappedabnormally,largerbub-bleswillbeformed,andthefinalproductwillhavelessvolumeandacoarsegrain.

Theeffectofshorteningisatitspeakwhentheingredientsaremixedthroughthecreamingmethodinwhichshorteningandsugararemixedasairisincorpo-rated;withtheremainingmethods,shorteningalsoexertsconsiderableinfluence.

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Inthecreamingmethod,shorteningsmustbesolid,sothatairdoesnotescape,andplastic,sothatbubblescanbesurrounded.Thepresenceofemulsifiersalsocontributestoabetterdispersionoftheentrappedairbubbles.Intheone-stageproductionmethod,airisentrappedinthewaterphaseandstabilizedbyeggpro-teinsandflour;fatstendtohaveadefoamingeffect.Topreventthis,anemulsifierisincludedintheshortening.Cakesproducedwithoilaremoretenderandexhibitbettermoistnessthanthoseproducedwithfats,althoughtheirgraintendstobecoarser.Ithasbeenshownthatthepresenceofsaturatedfattyacidsimprovesairabsorptionduringcakebattermixing.Infact,hydrogenationandtheincorpora-tionoffatswithhighermeltingpointsimprovethecreamingqualityofoils.Theformation of a structure incorporating small air bubbles thinly dispersed alsoimprovesthestabilityofthebatterandpreventstheescapeofthebubblestowardthesurfaceandthecollapseofthedoughduringbakingbeforedoughsettinghasoccurred.

Fatsalsoimprovetheeatingqualitiesofcakesastheyhelptocreateamoreten-dertexture;theyallowincreasesinthecontentofotheringredientssuchassugars,milk,oreggs;and incertain instances, likebutteror lard, theycanactasflavor-ingagents.Finally,fatsextendtheshelflifeofcakesbyslowingtherateofstalingthroughtheirinfluenceintheretrogradationofamylopectin.

... Cookies

Asincakes,fatshaveanimportantfunctionintheincorporationofairincookiedoughs.Theyalsodeterminetheconsistencyandstickinessofdoughsthathavetomeettheparticularrequirementsofeachproductionprocess;forexample,theymustextrudesmoothlyandshouldnotsticktosurfaces.Differentamountsandkindsofshorteningwillmodifycookiespreadduringbaking,althoughthesugarcontentintheformulationwillalsobeadeterminingfactor.Indoughswithhighsugarcon-tents (90%of theflourweight),an increase inshorteningfrom35 to55%lowersspreadabout10%.However,indoughswithasugarcontentof50%offlourweight,asimilarincreaseinshorteningwillleadtoanincreaseinspreadofapproximately25% (Stauffer, 1996). Variation in other ingredients or in the kind of shorteningusedresultsindifferentspreadingrates.Ingeneral,reducingshorteninglevelsgivescookiesofgreaterfracturability(Baltsaviasetal.,1999)andhardness(Sudhaetal.,2007).

... fillings

Fillingsused in theproductionofcertainsweetgoods, suchassandwichcookiesorsugarwafers,aremainlycomposedofsugarandfat.Thekindandamountoffatusedwill influence air incorporation, consistency, stickiness, andmouthfeel.Theconsistencyoffillingsmustbesuchthattheycanbereadilyextrudedorspreadovercookies,wafers,orcakes;theymustbefirmatambienttemperatureandoccasionally(cookiesandwafers)stickyenoughtoholdontothecookie.Fatmustalsomeltinthemouthtoavoidawaxymouthfeelandprovideacoolingeffect.

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. generalstrategIesforthe suBstItutIonofsugarsandfats

Whenmanufacturersembarkontheproductionofsugar-andfat-freeproducts,theyusually rely on the use of alternative products, although in certain situations theoptionofreformulatingtherecipesshouldnotbecompletelydisregarded.Ifsubsti-tutesaretobeused,theyshouldmeetthefollowingrequirements:

1.Besafeandcomplywithnationalandinternationalregulations 2.Haveflavorcharacteristicssimilartothoseofregularproducts 3.Bestableunderprocessingconditions(pH,temperature,etc.) 4.Besoluble 5.Possessnutritionalcharacteristicsadequatetotheneedsoftheproduct 6.Bereasonablycosteffective

12.4.1 suGarrePlaCers

Productdevelopershavefollowedthreedifferentapproachesintheirsearchfornewsugar-freeproducts.Thefirstapproachhasfocusedonthesubstitutionofsucrosebyadifferentsugarcapableofminimizingtheadverseeffectsassociatedwithsucroseconsumption.Infact,theseproductsshouldnotbelabeledas“sugar-free,”becausethe substituting substance is another sugar.Fructosehasbeenusedmostly in theproduction of foods for diabetics. The second approach opts for the introductionof intense sweeteners. As these products possess greater sweetening power thansucrose, theycanbeused insmallerdosesand thusasharpfall incaloric intakeoccurs.Theyrepresentaveryattractiveoptionforthedevelopmentoflow-caloriecarbonatedbeverages;inbakedgoodsthough,sugarismuchmorethanjustaflavorenhancerandadifferentsolutionmustbefound.Whenthemainfunctionofsugaristoprovidevolumeandtexture,asitisthecaseinmanybakedgoods,thendevelopershaveusuallyappliedthethirdapproach—theintroductionofbulkingagents,aloneorincombinationwithintensesweeteners.Inallcases,acarefulconsiderationofthesynergisticeffectsofdifferentsugarreplacersisnecessarytooptimizethesensorycharacteristicsofthefinishedproduct(Hangeretal.,1996;Montijanoetal.,1998).Comprehensivereviewsdealingwithmostofthesepointshavebeenpublishedovertheyears(Beereboom,1979;FryeandSetser,1993;Giese,1993;Newsome,1993;OlingerandVelasco,1996;Shinsato,1996).

... fructose

Inadditiontoglucose,fructoseisoneoftheconstituentmonosaccharidesofsucrose,and, as its name indicates, it occurs in many fruits. Like sucrose and glucose, itacts as substrate, fermentablebybaker’s yeast, promotes thedevelopment of tex-tural properties in baking products, and affects the final color through Maillardandcaramelizationreactions,thoughaslightlydifferentcolorthanthatprovidedbysucroseresults.Fructosehasasweeteningpowergreaterthansucrose(1.8greater),sosmalleramountsareadequate,andthereisasignificantcaloricreductioninthefinishedproduct.Thechiefadvantageoffructoseisitslowglycemicindex;diabet-

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icstolerateitmuchbetterthansucroseasnoinsulinisneededforitsmetabolism.However, tolerance is not complete, and diabetics are advised to refrain from anindiscriminateconsumptionofproductscontainingfructose.

Althoughfructoseisanidealreplacerofsucroseincertainproducts,itshouldalwaysbekeptinmindthat,likesucroseorglucose,itisjustanothersugar.There-fore,anylabelingofproductswithfructosestating“nosugaradded”canbeconsid-eredmisleading.Incertaincountries,labelscanbecurrentlyfounddeclaring,“nosugar,withfructose”or“nosugar,nofructose.”Anotheraspecttobeconsideredisthatfructosehasasimilarcaloricvaluetosucrose;thus,theonlywayofobtainingacaloricreductioninthefinishedproductistoloweritscontentintheformulation.Moreover,fructosecanbeafactorinthedevelopmentofdentalcaries,anditseffectondiseasessuchascardiovasculardiseaseisstillunderstudy.

... Intensesweeteners

12.4.1.2.1 SaccharinSaccharinisasugarsubstitutewithasweeteningeffectbetween300and500timesgreaterthansucrose,butitisnotmetabolizedinthehumanorganismandisexcretedintheurinewithoutprovidingcalories.SaccharinisstableunderthepH,moisture,andtemperatureconditionsundergonebybakedgoods,anditalsoshowsadequatesolubility.Anadditionaldesirablepropertyisitssynergisticeffectwithothersweet-enersandbulkingagentswhichresultsinanenhancedsweeteningeffect.Themaindrawbackisthatsignificantnumbersofconsumersdetectaslightlybitteraftertaste.Forthispurpose,acombinationofsaccharinandcyclamateisideal,asthelattercanpartiallymasktheunpleasantaftertaste.

Saccharinwaswidelyusedforover100yearsinallkindsoffoodsandbever-ages. Consumption reached its peak during the 1970s when it was the only low-caloriesweeteneravailable.Itwasusedasacoffeesweetenerorinotherproductsdestined for diabetics or concerned overweight people. For many, it became partof their daily lives. Now, although it has been pushed aside by newly developedsweetenerswithbetterorganolepticcharacteristics,itsverylowcoststilljustifiesitsinclusioninbeverages,chewinggums,jams,andsauces.ItsAcceptableDailyIntake(ADI)is5mg/kg.

12.4.1.2.2 CyclamateThesweeteningeffectofcyclamateis30timesgreaterthansucrose,withapleasanttastethatissimilartosucrose.Cyclamateexhibitsgoodsolubilityandstabilityoverawiderangeoftemperatures.Unlikesaccharin,itdoesnotleaveabitteraftertaste,but the sweetness sensation,althoughpersisting longer,hasamoredelayedonsetthansucrose.Cyclamateissynergisticwithmostsweeteners,masksbitterness,andiscapableofenhancingsomeflavors.Eventhoughasmallsectionofthepopulationcanmetabolizecyclamate,mostpeopleareunable,andhenceitisconsideredasanoncaloricsweetener.

Cyclamatewasfirstmarketedduringthe1950s,butinthelate1960s,itssafetywasquestionedwhenevidencefromstudieswithratsbecameknown.Abaninmanycountriesensued.Today,havingbeendeclaredsafeforhumanconsumption,ithas

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beenreintroducedinmanycountries.ItsADIis11mg/kg.It isnowusedinlow-caloriebeveragesorchewinggums.

12.4.1.2.3 AspartameAspartameis180to220timessweeterthansucrosewithasimilartaste.Likeothersweeteners,aspartamehassynergisticeffectandenhancesflavors,namelyacidfruitflavors. Its tendencytodegradeathightemperaturesconstitutes itsmaindrawbackwhenaddedtobakedgoods.Hence,itsuseisinadvisablewhenbakingprocessesareinvolved.Anexpensiveencapsulatedversioncapableofwithstandinghightempera-tureshasbeeninthemarketforanumberofyears.Aspartamecanbeusefulinthepro-ductionofcreamsandotherproductsthatneednotundergosevereheattreatments.

Aspartame has currently become the most widely used sweetener in the foodindustry, even though itwasnot approveduntil theearly1980s. It ismetabolizedin the intestinal tractproducingaspartic acid,phenylalanine, andmethanol.Afterextensivestudiesconfirmeditssafetyforallpopulationgroups,itwasapprovedbythe European Union with an ADI of 50 mg/kg, the equivalent of a daily sucroseintakeof600gforapersonweighing60kg.However,asmallnumberofindividualswiththediseasephenylketonuria,intoleranttophenylalanine,mustlimitaspartameintake.

12.4.1.2.4 Acesulfame-KDiscoveredin1967,acesulfame-Khasbynowbeenapprovedinmostcountries.Itisnotmetabolizedandisthereforecompletelyexcretedwithoutprovidingcalories.IntheEuropeanUnionitsADIis9mg/kg,andintheUnitedStatesitis15mg/kg.Acesulfame-Kpresentsacleantaste,noaftertaste,anditssweetnessdoesnotlast,though is rapidlyperceived.When in combinationwithother sweeteners, acesul-fame-Kexhibitssynergisticeffectsandacertaincapacityformaskingoff-flavors.Itis200timessweeterthansucrose.ThiscompoundisstableunderawiderangeofpHandtemperatureconditions,and, inparticular, itcanwithstandbakingconditionscommonintheprocessingofbakeryproducts(Klugetal.,1992).

Thereareotherintensesweetenersapprovedassugarsubstitutesundertheregu-lationsofdifferentcountriesorwithapplicationsforuseandregulatoryreviewsstillpending(e.g.,taumatine,neohesperidineDC,sucralose,andalitame).Allofthesesugarsubstitutesfaceregulatoryoreconomicdifficulties.

... Bulkingagents

12.4.1.3.1 PolyolsPolyolsareobtainedbythecatalytichydrogenationofdifferentsugars.Thesesub-stancesaresimilartosucroseforthetexturecharacteristicsandvolumestheyprovidebutwithoutpromotingdentalcaries,withbettertoleranceratesamongdiabetics,andwithlowercaloricvalues.Theirmainlimitationisthattheirsweetnessisbelowthatofsucrose.Table12.1showsthesweetnessofseveralsugarsubstitutes.Further,aspolyolsarenotinvolvedinprocessessuchasMaillardorcaramelizationreactions,theyalsoperformlessdecisivelythansucroseinthedevelopmentofcrustcolor;fin-ishedproductscontainingpolyolsusuallyexhibitlightercolors.Butpolyolssurpasssucroseasinhibitorsofbacteriaandmoldgrowthandhavehighhygroscopicity.

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Insomepeople,anexcessiveconsumptionofpolyolsleadstointestinaldisor-ders, suchasapersistent laxativeeffectordiarrhea, reminiscentof theproblemscausedbyhighfiberintakes.Symptomswillvarywithindividualsandtherestofthediet,andthoughtheyarerarelysevereorlasting,arestrictiveintakeisadvisable.Polyolsareabsorbedinthesmallintestineinaslowandincompletemannerandareconvertedintoenergywith littleornoinsulinbeingrequired.Eachpolyolhas itsownspecificcaloricvalueandtheaveragevalueisconsideredtobe2.4kcal/g.

Maltitol is one of the most widely used polyols among bakers, because itsfunctionalproperties (hygroscopicity, solubility,meltingpoint)make it similar tosucrose.Itscaloricvalueis3kcal/g,anditssweeteningeffectisabout80to90%ofthatofsucrosewithoutobjectionableaftertaste.Consideringitscoolingeffect,itisbelowsorbitolandxylitolbutabovesucrose.Itcanbeoptimallyadaptedtochocolatemanufacturingbecauseofameltingpointsimilartothatofsucrose(Rapailleetal.,1995).Secondintherankingofpolyolsmostwidelyusedinbakedgoodsissorbitol.Itscaloricvalueis2.6kcal/g,andcomparedwithsucroseithasasweeteningeffectof60%. It doesnothaveanydifficulty in solubilizing. It is ahighlyhygroscopicpolyolusedasahumectantinthecommercialproductionofbakedgoodstodelaystaling.Fromaneconomicstandpoint,bothmaltitolandsorbitolareverycost-effec-tivesugarreplacers.Inaddition,theuseofhydrogenatedstarchhydrolysatesiswide-spread;thisisageneraltermusedtorefertoblendsofpolyols.Thefinalproductisablendofsorbitol,maltitol,andotherlargerhydrogenatedsaccharideswithdifferingproperties(sweeteningeffect,hygroscopicity,solubility,etc.)dependingontheman-ufacturingprocess.Caloricvaluesarebelow3kcal/g,andtheirsweeteningeffectsrangebetween40and90%.

Lactitolandisomalt,havingverylowhygroscopicity,arewidelyusedwithlowmoistureproductssuchascookiesandcandies.Theirenergyvalueis2kcal/g,andtheirsweeteningeffectsare30to40%forlactitoland45to65%forisomalt,alwaysinrelationtothesweeteningeffectofsucrose.Isomalt,likexylitol,preventstooth

taBle.

relativesweetnessofsomesugarsubstitutessugars

Sucrose 1 Polyols

Fructose 1.2–1.8 Xylitol 1

high-Intensitysweeteners Maltitol 0.85–0.95

Acesulfame-K 130–200 Sorbitol 0.55–0.7

Aspartame 180–220 Isomalt 0.45–0.65

Saccharin 200–700 Lactitol 0.35

Cyclamate 30 Erythritol 0.65

oligosaccharides Mannitol 0.5

Polydextrose 0 Hydrogenatedstarchhydrolysates

0.7–0.9

Oligofructose 0.3–0.5

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decay.Infact,xylitoliscommonlyusedintoothpasteandotheroralhygieneprod-ucts.Xylitolispossiblythemostsuitablereplacerfortheproductionofsucrose-freeproducts,butitsapplicationshavebeenlimitedduetoitshighcost.Insweetnessandsolubility,itissimilartosucrose,anditsenergyvalueisonly2.4kcal/g.Withhighhygroscopicity,itcanactasahumectant,anditscoolingeffectisfairlyhigh.

Maltitolistheleastadaptabletothenecessitiesofthebakingindustry,asithasahighlaxativeeffect,lowhygroscopicity,andalowsweeteningeffect(40to50%ofsucrose).Itscoolingeffectisnotonlyinferiortothatofsucrosebutiswellbelowtherestofthepolyols.Erythritolisnotverywidelyusedinthebakingindustry.Itsstrong laxative effect and low to medium solubility limit the number of possibleapplications.Ithasasweeteningeffectrangingfrom60to70%ofthatofsucrose,anditscoolingeffect,althoughhigherthanthatofsucroseormaltitol,islowerthanthatofxylitolandsorbitol.InJapan,ithasbeeninusesincethe1990sbutisstillunder reviewin the restof theworld. Itsmainadvantage is its lowenergyvalue,approximately0.2kcal/g.

12.4.1.3.2 OligosaccharidesPolydextroseandoligofructosebelongtotheoligosaccharidesgroup.Bothcompoundsaremadeupofglucoseorfructosebranchedchainswithaveryslightmetabolizationinthehumanbody,andthuswithanegligiblecaloriceffect.Likedietarysolublefiber,they canprovide similarnutritionalbenefits and,with excessive intake, a laxativeeffect.Theyarenotcariogenicandarebettertoleratedbydiabeticsthansucrose.

Polydextroseisabranchedglucosepolymercontainingamountsofsorbitolandcitric acidwitha caloricvalueof1kcal/gandamaximumdaily intakeof50 to90 g. When first marketed, polydextrose was acid, yielded some unusual flavorsandfatrancidity,buttheseproblemshavebeenovercomewithanewlydevelopedimprovedversionofpolydextrose.Asitssweeteningpowerislimited,polydextrosemustbeblendedwithsomeintensesweeteners;nevertheless,itimpartsaverycleanflavor,withoutundesirableaftertasteorincompatibilitieswithothersweeteners.Inthedevelopmentoftextureandvolumeinbakedgoods,itissimilartosucroseandpresentsgoodsolubility.Highlyhygroscopic,itkeepsfreshnessinfoodsandcanbeusedasahumectant.Inadditiontoasugarreplacer,polydextrosecanbeusedasafatreplacer.

Oligofructoseisacomplexofshortbranchedchainsoffructoseobtainedfrominulin,achicoryrootextract.Inulinhasthesamecompositionbutahighermolecularweight,anditsbestapplicationisasafatreplacer.Likepolydextrose, ithasa lowsweeteningeffectandnocoolingeffectbutacleantaste,andinitsabilitytoimparttextureandvolumetothefinalproduct,itissimilartosucrose.Nevertheless,itsmainadvantagesarerelatedtonutritionalbenefits.Itscaloricvalueis1.5kcal/ganditactsassolublefiber,helpingdigestedfoodpasseasilythroughtheintestinaltract,increas-ingfecalbulk, reducingconstipation,andfacilitatingbowelmovement.Accordingto some studies, oligofructose seems to reduce cholesterol and triglyceride levels.Finally,oligofructosepromotestheproductionofbifidobacteriaintheintestinaltract(prebioticeffect)andcalciumabsorption.

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12.4.2 FaTrePlaCers

Toreducethefatcontentofafooditem,manufacturershavefavoredtheintroduc-tion of fat replacers, ingredients combining some of the functional properties offatswithlesscaloriceffect.Fatreplacersarealsoknownasfatmimetics,andtheycanbebasedoncarbohydrates,proteins,fats,oracombinationofthese.Asecondoptionformanufacturershasbeentousefatextenders,productsoptimizingfatfunc-tionalityandallowingareductionintheamountoffatincludedintheformulation.Comprehensivereviewsofthecharacteristicsandapplicationsoftheseproductscanbefoundintheliterature(ADA,2005;FryeandSetser,1993;Gluecketal.,1994;LuccaandTepper,1994).SomeofthemostcommonlyusedfatreplacersandtheirmanufacturersareshowninTable12.2.

... Carbohydrate-BasedfatMimetics

Theseproductsarecapableofabsorbinglargeamountsofwatertoformagel-likematrixwithsomeofthefunctionalpropertiesoffats.Theyaresimilartofatsinthepropertiestheyinfluence:viscosity,body,creaminess,andmouthfeel.Becausetheyaremixedwithwater, theircaloricvalueisreducedto1to2kcal/g,eventhoughcarbohydrates can provide 4 kcal/g. Fibers, cellulose, and gums have no caloriceffect.Theirusewithfriedgoodsisnotrecommended,andtheirhighmoisturecon-tentincreaseswateractivitywithgreaterriskofpromotingmicrobiologicalgrowthandthusreducingshelflife.Thisgroupoffatmimeticsincludesmodifiedstarches,fibers,cellulose,gums,maltodextrinsanddextrins,polydextrose,andinulin.Bothpolydextroseand inulinwerediscussedin theprevioussectionasbulkingagents,andtheycanreplacesugarsaswellasfats.

12.4.2.1.1 Starch DerivativesTheseproducts,includingmodifiedstarches,maltodextrins,anddextrins,aremixedwith threepartsofwater,aregel-like,andprovide textureandmouthfeelusuallyassociatedwithfats.Theircaloricvaluewillbeof1kcal/ginsteadof9kcal/glikefats. Modified starches are obtained through physical or chemical treatments ofnativestarchessothattheycanwithstandextremeconditions(temperature,acidity,shear)andaltertheirpastingbehavior.Finalcharacteristicswilldependonthepar-entstarchandthemodificationsithasbeenforcedtoundergo.Itwasreportedthatsmall-granulestarchhavingagranulediametersimilartothatoflipidmicelles(lessthan2µm)mighthavepotentialasafatreplacer(LuccaandTepper,1994).Malto-dextrinsanddextrinsarehydrolyzedstarcheswithadextroseequivalenceof lessthan20,whichmayresultindarkcolorswhenheatprocessed,butthisshouldnotpreventitsuseinbakedproducts.Modifiedstarches,maltodextrins,anddextrinscanmaskcertainflavorsandimpartnewonesdeservingspecificattention.

12.4.2.1.2 Gums and CelluloseNeitheroftheseproductsisabsorbedintheintestinaltract,andtheycanbeincludedinthefibergroup;theyprovidenutritionaladvantageswithnocaloriceffect.Gumsarehydrocolloidswithgreatcapacityforwaterabsorptionwhichcanimpartviscos-ity,stabilizewatersystems,andinhibitsynerisis.Examplesofgumsincludexanthan,locustbean,carrageenan,andpectin.Pectin isusedprimarilyasagellingagent.

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taBle.

fatreplacerstype Brandname Manufacturer

Carbohydrate-based

Cellulose Avicel FMCCorp.

Novagel FMCCorp.

Modifiedstarches Stellar A.E.StaleyMfg.Co.

Sta-Slim A.E.StaleyMfg.Co.

Amalean AmericanMaize-ProductsCo

N-lite NationalStarch&ChemicalCo.

Maltodextrin Paselli(potato) Avebe

Oatrim(oat) Rhone-Poulenc

Maltrin(corn) GrainProcessingCorp.

N-Oil(Tapioca) NationalStarch&ChemicalCo.

RiceTrin(rice) ZumbroInc.

C*Light Cerestar

Fibers WonderSlim NaturalFoodTechnologies

Z-Trim FiberGelTechnologiesInc.

Betatrim Rhone-Poulenc

DairyTrim MeyhallChemicalAG

Polydextrose Litesse CultorFoodScience,Inc.

Inuline Raftiline Orafti

Pectin Slendid HerculesInc.

Grindsted Danisco

Gums Kelgum Kelco

Kelcogel Kelco

Nutricol FMCCorp.

Protein-based

Microparticulateprotein Simplesse TheNutraSweetCo.

Wheyproteinconcentrate Dairy-Lo CultorFoodScience,Inc.

Nonfatmilk,gums,modifiedstarch,andemulsifiers

N-Flate NationalStarch&ChemicalCo.

fat-based

Alteredtriglycerides Salatrim Nabisco

Caprenin Procter&GambleCo.

Benefat CultorFoodScience,Inc.

Sucrosepolyester Olean Procter&GambleCo.

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Cellulosegelsormicrocrystallinecelluloseresultfromtheprocessingofnonfibrouscellulosetoreduceparticlesizeinsuchawaythatbetween60and70%ofparticleshavelengthsoflessthan2microns.Thecellulosemicrofibersjoinotheringredients,suchascarboxymethylcelluloseorguargum,toholdtogetherasanetwork.

... Protein-BasedfatMimetics

Thereisapatentedproceduretoobtainmicroparticulatedproteins.Thisprocedureconsists of the simultaneous application of two processes—pasteurization (heattreatment)andhomogenization (highshear),producingsphericalproteinparticlesoflessthan2micronsindiameter.Whey,milk,andeggproteinsaretheusualrawmaterials,andpeoplewithallergiesshouldrefrainfromconsumingtheseproducts.Becauseofparticlesizeandshape,thetonguefailstodetecttheindividualparticlesandinsteadperceivesacreamy,smooth,andfluidproductcoatingmouthsurfacesinwaysusuallyassociatedwithfats.Thiscoatingactionhelpsflavorsreachthetastebudsmoregradually,but it alsomasks somebitter andastringentflavorscharac-teristicof low-fatproducts.Microparticulatedproteins,marketedinseveralformsunder the trademarkSimplesse®, tend to imbibewater in suchaway that1gofprotein-basedfatmimeticscanreplace3goffatwiththeresultingcaloricreduction.Likecarbohydrate-basedfatmimetics,theyareunsuitableforusewithfriedfoods,althoughsomeversionswithstandheatprocessingbetterthanothers.

Anadditionalfatsubstitute isderivedfromwheyprotein,modifiedthroughatreatmentcombiningheatingandanacidicmedium.Changesinproteinconcentra-tion,temperature,andpH,andthepresenceofotheringredientsresultinawiderangeofproductswithvaryingfunctionalproperties,includingopacity,waterabsorptioncapacity,particlesize,andemulsifyingcapacity.Finally,fatsmayalsobepartiallyreplacedbyproductscomposedofablendofanimalandvegetableproteinswithgums,starches,andwater.

... fat-Basedreplacers

Fat-basedfatreplacersarelipidsmodifiedorsynthesizedinsuchawaythattheyarenotfullymetabolizedinthehumanbody,andthustheircaloriceffectisbelowthe9kcal/glevelofconventionalfats.Intheirphysicalproperties,theyaresimilartofats.Theycanwithstandhightemperatures,includingfrying,andcanreplacefatstotallyorpartially.

Oneof thebestknown isCaprenin, formedbyesterificationofglycerolwiththreefattyacids(capric,caprylic,andbehenic).Itispartiallyabsorbedintheintes-tineandprovidesonly5kcal/g.Capreninissimilartococoabutterandiscommonlyusedasareplacerinsoftcandyandchocolateconfectionerycoatings.Salatrimisasimilarproduct,obtainedbyesterificationofmonostearinwithshort-chainacids(acetic, propionic, andbutyric).The resultingproduct provides just 4 kcal/gwithvaryingplasticpropertiesdependingontheratioofshort-chainfattyacidsused.Itthushasthecapacitytoreplaceall-purposeshorteningsaswellasfillerfats.

Inaddition,therearesubstanceswiththermalandorganolepticpropertiessimi-lartofats,toolargeforintestinalabsorption,unavailableforhydrolysisbygastricandpancreaticlipase,andprovidingnocalories.Thebestknownisolestra,asucrose

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polyestermadeupofhexa,hepta,andoctaestersofsucrose,esterifiedwithlong-chainfattyacidsderivedfromedibleoils,includingsoy,corn,andcotton.Byvary-ingthedegreeofesterificationandthenumberoffattyacidsused,itispossibletoobtainawiderangeofproductswithfunctionalproperties,appearance,mouthfeel,stability, shelf life, and organoleptic characteristics usually associated with con-ventionalfats.Althoughatonetime,insomecountries,manufacturerswishingtoincludeolestraintheirproductswererequiredtoaddfat-solublevitamins(A,D,E,andK)andwarnonthelabelthattheabsorptionoffat-solublevitaminscouldbeinhibited,currently,aftermuchevidenceaccumulatedovertheyears,thishascometobeconsideredasanunnecessaryprecaution.

Emulsifierscanbehaveasfatextenders.Theircaloriceffectisthesameasthatoffats(9kcal/g)but,asonlybetween25and75%ofemulsifierisnecessarytomimictheeffectofconventionalfats, there isasignificantcaloriereduction.Emulsifiersareusedtoreplaceallorpartofthefatcontentincertainproducts.Inothers,theyalsohelpretainmoistureandincreasevolume.Themostwidelyusedemulsifiersinthemanufacturingoflow-fatproductsaremonoglyceridesandpolysorbates;inotherapplications,manufacturerscanalsouselecitin,sodiumstearoyllactylates(SSLs),ordiacetyltartaricestersofmono-anddiacylglycerols(DATEM).Blendsofemulsi-fiersaggregatethefunctionalpropertiesoftheseparatecomponents.

. suBstItutIonofsugarand fatsInCaKesandCooKIes

12.5.1 suGarsuBsTiTuTion

... Cakes

Strategies for theproductionof sugar-free cakes are usuallybasedon the substi-tution of sugar by one or a combination of bulking agents capable of yielding afinishedproductwithadequatevolume,texture,andgrain.Ithasbeenestablishedthatdifferentbulkingagentsaffectthebehaviorofdoughsduringbakinginvaryingdegrees,therebyaffectingtheeventualvolumeandstructure(Ikawa,1998).Rondaetal.(2005)comparedthecapacityofsevenbulkingagentsassugarsubstitutesinspongecakes.Topperformerswerexylitol andmaltitol, followedby sorbitol; thehighpriceofxylitol,however,hasresultedinitsbeingsupersededbymaltitolasthemostwidelyusedinsugar-freecakemanufacture.Thesamestudypointedoutthatcakesmanufacturedwithpolyolsyieldedlightercakesbecausetheyareunaffectedby Maillard reactions. Conversely, those cakes manufactured with oligofructoseandpolydextroseresultedindarkercolors,asrepeatedlyreportedbyotherstudies(Estelleretal.,2006;Hicsasmazetal.,2003)andsuggestingthatthecombinationofthesebulkingagentswithpolyolsassugarsubstitutesmayprovidepositiveresults(Penna et al., 2003). In fact, Frye and Setser (1992) optimized a sugar-free cakeformulationusingblendsof polydextrose anddifferent polyolswithgood results.Moreover,emulsifierscanbeusedtobuffertheadverseeffectsofthesubstitutionofsugarbybulkingagents(KamelandRasper,1988).Intheseinstances,acorrectchoiceoftypeanddosageofemulsifierisessential.

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Apartfromtheirappearance,volume,andtexture,sugar-freeproductsmustalsobeassessedbytheirflavorandaroma.Itisanestablishedfactthatdifferentbulk-ingagentsexhibitvaryingsweeteningeffectsaswellasdiversearomaticandtasteprofiles. In some formulations, particularly when using bulking agents with lowsweeteningpower,suchaspolydextrose,theadditionofanintensesweetener,likeacesulfame-K,aspartame,oranyother,mayberequired(Attiaetal.,1993;Free-man,1989).Somesugarsubstitutescauseanunpleasantaftertaste,likesometypesofpolydextrose(FryeandSetser,1992),andhavetobemaskedbyothersweeteningorflavoringagents.

Overall,itisdifficulttomakegeneralrecommendationsforthesubstitutionofsugar in cakes.Thedivergenceofviews reported in the literaturehighlights thatdifficulty.Thus, it is known thatpolydextrose raises the temperatureof thegela-tinizationofstarch(Paterasetal.,1994)andlowersbatterstability(Hicsasmazetal.,2003).This, in turn, affectsair retentionduringbaking, theexpansionof theproduct,andthefinalvolume.However,althoughHicsasmazetal.(2003)foundthatcakesmanufacturedwithpolydextroseas sucrose substitute showedfineanduni-formgrain,Koceretal.(2007)reportedoppositeresults.Ontheotherhand,Rosen-thal(1995)suggestedthattheriseinthestarchgelatinizationtemperatureproducedbypolydextrosecanbeusedtoimprovethemanufactureofcakeswithagedeggsasaresultofanincreaseintheeggproteindenaturationtemperature.Allthesedif-feringresultsindicatethatcakemanufacturingdependsontheinteractionofmanyfactors, for example, the type of cake sought, formulation, and raw materials. Ineachparticularformulation,therefore,differentblendsofsugarsubstitutesshouldbetested,andthentheresultsverified,includingboththephysicochemicalandsensorypropertiesofthefinishedproduct.

... Cookies

Strategies for theproductionofsugar-freecookiesclosely resemble thosealreadydiscussedforsugar-freecakes.Theremovalofsugarbringsaboutdrasticchangesindoughsandinthefinishedproducts,andthesecannotbeminimizedjustbytheintro-ductionofintensesweeteners(Limetal.,1989).Incookies,sugarandfatreplace-ment can affect texture to a greater extent than flavor (Perry et al., 2003). Thus,theadditionofabulkingagentoracombinationofseveralofthemisnecessarytocontrolthechangesinthetextureofdoughsandcookiesduetotheremovalofsugar.Zouliasetal.(2000a)comparedthefunctionalityofseveralbulkingagentsassugarreplacers in cookies. Cookies with maltitol scored the highest results in hedonicevaluations,evenhigherthanthecontrol,andtheywerealsoconsideredassimilartotheoriginalproductinshape,color,andtexture.However,sugarreplacementwithmaltitol significantly impacted dough adhesiveness and cohesiveness, an impor-tantpointinthecommercialproductionofcookies.Thesameauthorsobservedanimprovedacceptabilitywhenanintensesweetener(acesulfame-K)wasaddedtothesugarless cookies, even with sugar replacers, like fructose, of greater sweeteningeffectthansucrose.Maltitolhasbeenshowntohavebettercharacteristicsthanotherbulkingagentsassugarsubstituteinlow-fatcookies(Zouliasetal.,2002a).

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Anotherbulkingagentcommonlyused,aloneorcombinedwithpolyols,inthemanufactureofsugar-freecookiesispolydextrose.Becauseofitsverylowsweet-ening effect, it must be supplemented with an intense sweetener. The choice ofsweetener,orblendofsweeteners,isthenoftheutmostimportance,iftime-intensitysweetnessandbitternesscurvessimilartothoseofsucrosearetobeattained(Limetal.,1989).Whenselectingasugarsubstitute,itisequallyimportanttotestitseffectontheshelflifeoftheproduct,asdifferentbulkingagentsimpactdifferentlyonthestabilityoffatspresentincookies(Ochietal.,1991).

Evidenceprovidedbydifferentstudiesonthemanufactureofsugar-freecookiesisvalidunderaparticularsetofconditionsandmust,therefore,becarefullytestedwhenappliedtonewformulations,typesofcookies,orprocessingconditions(com-mercialscale).Inanycase,allthisexperimentationhasincommonthesubstitutionofsugarbybulkingagentsand,sometimes,intensesweeteners,acarefulmonitoringofthephysicalcharacteristicsofdoughsandcookies,andthesensoryacceptabilityofthenewlydevelopedproduct.

12.5.2 FaTsuBsTiTuTion

... Cakes

Obtainingfat-freebakingproductswithsensorycharacteristicssimilartotheregularproductsisaformidablechallenge,becausenofatreplacercurrentlyinuseexhibitsperfectstructuralsimilarity(Shukla,1995).Toovercomethisobstacle,ithasbeennecessarytodevelopblendsoffatreplacers,changethedoses(1:1ratiosbeingnotalwaysadvisable),andevenreformulatetheproduct.

Broadly speaking, carbohydrate-based fat replacers are the most widely usedintheprocessingoffat-freecakes,owingtotheircapacitytoprovideproductswithgoodorganolepticproperties (Bathetal.,1992;Swansonetal.,2002),whichcaneven be improved by the addition of emulsifiers (Khalil, 1998). The substitutionof fatsbymaltodextrins incakescausesa reduction inbatterviscosity,which, inturn,leadstoasmallerfinalvolume(Lakshminarayanetal.,2006).Thesamestudyreported that thebest resultswereobtainedwhen theamountof fat removedwasreplacedbyasmalleramountofmaltodextrin,approximately50%,althoughcakesthus manufactured exhibited moderately sticky texture and mouthfeel. Moreover,itwasshown that theadditionof smallamountsofglycerolmonostearate (GMS)improvedvolume,entrapmentofairinthebatter,andthesensoryqualityofthecake,withlessdensecrumbgrainandlessstickytexture.Theadditionofsodiumsteroyllactylate,however,failedtoyieldthesamebeneficialeffects,provingthatthechoiceofanappropriateemulsifierisessential.Incakesprocessedwithmaltodextrinasfatreplacer,theirphysicalandsensorycharacteristicscanalsobeimprovedbyaddingcornamylodextrin(Kimetal.,2001).

Anumberofsignificantfatreplacersusefulintheprocessingofcakeswithlowerfatcontentsareincludedinthesamegroupasfibers.Goodresultscanbeobtainedwithinulinandoligofructose(Devereuxetal.,2003),polydextrose(FryeandSetser,1992),fiberproductsderived fromcornandoats (Warnerand Inglett,1997),andhydrocolloids,aloneorincombinationwithemulsifiers(Kauretal.,2000).Theseproductsprovideasignificantreductionincaloriccontent,negligiblecaloriceffect,

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and, in some instances, inaddition to thecaloric reduction,a lowerflourcontentbecomespossible.However,productsincludingthesesubstitutestendtoscorelowervaluesinthehedonicscaleifcomparedwiththeoriginalproducts,onaccountofthechangesthatoccurinthetextureofthefinishedproduct.Furthermore,excessiveconsumptionoftheseproductsmayhaveadversephysiologicaleffects.

... Cookies

Although several studies about theprocessingof fat-freecookieshavebeenpub-lished,nocomprehensivecomparisonofallthedifferentsubstitutesisyetavailable.Fat-free formulations for cookiesyielddoughsdrasticallychanged in textureandfinishedproductswithdifferentphysicalandsensorycharacteristics.Thesechangescanbeminimizedbyincludingintheformulationdifferentfatreplacers,althoughinallcases,acceptabilityisnotaswideaswiththeregularproducts.Cookieswithlowfatcontenttendtoexhibitlesssurfacecracking,fewersurfaceprotusions,moreuniform cells, and more mouthcoating, apart from a different flavor (Armbristerand Setser, 1994). Carbohydrate-, protein-based, and fiber-derived replacers havebeentestedwithvaryingresults.Sudhaetal.(2007)establishedthattheadditionofmaltodextrinorpolydextrosereducedtheeffectsoffatremovalontheprocessingofcookies,andwiththeadditionofemulsifiersorguargum,thequalityofthefinishedproductapproachedthatoftheoriginalbutwasneverquitethesame.Sanchezetal.(1995)optimizedaformulationofreduced-fatshortbreadcookieswithdifferentfatreplacers.Thisstudyshowedthatcookieswithlowfatcontentexhibitedincreasedmoistureandtoughness,andlessspecificvolume;theadditionofemulsifiersledtoimprovedresults.Amodificationoftheprocessingofthedoughwasintroducedtoobtainlow-fatshortbreadcookies.Zouliasetal.(2002b)compareddifferentcarbo-hydrate-andprotein-basedfatreplacersandobservedsignificantdifferencesamongthevariousreplacers;thebestresultswereobtainedwithinulin(Raftiline),ablendofmicroparticulatedwheyproteinsandemulsifiers(Simplesse),andanoat-derivedproduct rich in ß-glucans (C*Light). Among all these, Simplesse yielded cookiesverysimilarindiametertotheoriginalcookiesbutwithhighervaluesofmoisturecontent(Zouliasetal.,2002a).

Additionalfatreplacers in themanufactureofdifferent typesofcookieshavebeentestedwithsimilarresults,includingoat-derivedfiberproducts(CharltonandSawyer-Morse, 1996; Conforti et al., 1997; Inglett et al., 1994; Lee and Inglett,2006),prunepaste (CharltonandSawyer-Morse,1996),hydrocolloid-basedprod-ucts(Confortietal.,1997),orokragum(Romanchick-Cerpoviczetal.,2002).Allofthemarecapableofminimizingtheeffectsoffatremoval,buttheyfailtomatchthephysicochemicalpropertiesoftheregularproducts.Ontheotherhand,thestrategyforthemanufactureoflow-fatcookiescannotfocusonanapproachbasedonasinglefatreplacerwhenablendofreplacersismorelikelytobesuccessfulinimprovingthefinalresult(Zoulias,2000b).Finally,theimportanceofreducingfatcontentinfillingsandicingsshouldnotbeoverlooked—thiscouldbeobtainedwiththerightblendofwheyproteinandhydrocolloids(Laneuvilleetal.,2005).

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. ConClusIons

TherecentgrowingawarenessoftheroleofdietinhealththroughoutmostWesterncountrieshaspromptedanincreaseintheconsumptionoflow-calorie,low-fat,andsugar-freeproducts.Thisholdstruenotonlyforcomparativelysmallsegmentsofthepopulationaffectedbycertainconditions,suchasdiabetes,requiringamanda-toryrestraintintheconsumptionoffatsandsugar,butalsoforagrowingnumberofconsumersoptingfor“ahealthylifestyle”asawayofpreventingfutureailments.As a result, significant attention has been focused on the development of bakeryproductssuchascakesandcookieslowinfatandsugar.Formanymanufacturers,thedevelopmentandmarketingofthiskindofproductsmusthavehelpeddiversifyproductionandwidenthemarketbyreachingtonewconsumersandgainingacom-petitiveadvantageoverrivalfirms.

Thedevelopmentof thesedietaryproducts isacomplex task,because itmayinvolve somethingelsebeyond themere substitutionof fats and sugar. It isoftenessentialtoreformulatetheseproductsandmodifytheirprocessingvariables.Mostapproaches,however,favortheutilizationofsugarandfatsubstitutes.Informationabout theinteractionsbetweenthesesubstitutesanddoughcomponents ishardtocomeby,inmanycasesitremainsunpublished.Draftingandpublicationofstudiesdealingwithsuchinteractionsandthewaytheyimpactontechnologicalprocesseswouldbehighlyusefulfortheformulationofbakinggoodslowinfatsandsugar.Ontheotherhand,thereismoreinformationavailableonthedevelopmentofthiskindofproductswhensugarandfatsarereplacedbyothertypesofingredients.Yeteachproductshouldbedealtwithindependently;itmightevenbenecessarytovarytheformulationinresponsetothedegreeofmechanizationintheprocessingofsuchgoods.Asuccessfuldevelopmentofbakingproductslowinfatsandsugardemands,first,athoroughunderstandingofthefunctionsoffatsandsugarintheprocessingandqualityofthefinalproductand,second,anequallythoroughunderstandingofthealternativeingredientsandthepossiblemodificationsintheproductionprocessaimedatimprovingthequalityofthefinalproduct.Finally,itshouldalwaysbekeptinmindthatthesuccessofthesedietaryproductsisnotjustduetotheirnutritionalcompositionbut,mostimportantly,isduetotheirorganolepticacceptabilityamongpotentialconsumers.Hence,studiesaboutthesensoryacceptabilityofnewlydevel-opedproductsbecomeessential.

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52748.indb 274 2/6/08 2:27:59 PM


IndexaAbboud,A.M.,19Acesulfame-K,259Acids,leavening,56-60,63Acrylamide,69-72Additives,functionsof,40-43Advantium®,235Agitatormixers,162-163Agyare,K.K.,125,136Alava,J.M.,107Alkalinewaterretentioncapacity(AWRC),11-12Alpha-linoleicacid,106Alveographs,13-14,122-123AmadoriandHeyn’sproducts,68Amaranthseed,198AmericanAssociationofCerealChemists

International(AACCI),4Ammoniumbicarbonate,37,52Amylodextrin,267Amylograph,11Antioxidantsformation,67-68Aromacompounds,formationof,65-67Ascorbicacid,143Ashcontentofwheatflour,10Aspartame,259Atherosclerosisandfats,250

BBaik,O.D.,100,174,193,198,205,206,207Baking

cake,156-157combinedtransportphenomenaduring,

180-184conductiveheattransferduring,175-176,177convectiveheattransferduring,176cookie,165-170crumbandcrustdevelopment,185-186evaporationonthesurfaceandmass

convectionduring,179heattransfermechanismsduring,174-178internalevaporationandcondensation,

179-180injetimpingementovens,220-223,232-235massdiffusionduring,178-179masstransfermechanismsduring,178-180microwave,223-231,232-235ovens,168-170radiativeheattransferduring,176,178soda,37,52-54volumeexpansionduring,184-185See alsoBakingtechnology

Bakingpowders,38,54-56doughandbatterreactionrates,60-61leaveningacids,56-60nutritionalvaluesof,61single-actinganddouble-acting,56

Bakingtechnologyjetimpingementoven,216-223research,215-216

Baltsavias,A.,131Bar-machinecookies,161Batter,cake

depositors,155-156emulsifiersin,107-110factorsaffectingrheologyof,102-116fatandfatreplacerin,104-107flourin,102-104hydrocolloidsin,110-113ingredients,91-94mixing,150-155reactionrate,60-61stabilityoffoamsandemulsionsin,87-89sugarin,110viscosity,62-63,95,99-100,106-107,108-

109,116See alsoCakes

Beta-glucan,106,268Bettge,A.D.,14,19Biscuitsandbiscuitdough

acrylmaidein,69fatin,36,135leaveningagentsin,38nonfatdrymilkin,40proteinsin,143,144saltin,39sugarin,35,128-129,130waterin,39

Blackbodies,178Bloodglucoseandsugar,248Bray,G.A.,250Breadandhydroxymethylfurfuralformation,

72-73,74-75Breakflour,4

yield,8Buhari,A.B.,195Bulkingagents,44,259-261

CCakes

baking,156-157cooling,157drymixes,91eggsin,36-37,43,93

52748.indb 275 2/6/08 2:28:01 PM


Index

emulsifiersinproductionof,90-91enzymesin,94-96,97fat-free,267-268fatin,35,81-82,92-93,255-256flourin,150-151flourparticlesizein,20foam,152,253high-ratio,16,84,95-96,97,112-113,251hydrocolloidsin,43leaveningagentsin,38lipidsin,21,94-96microwave-baked,227-228,229-231nonfatdrymilkin,40packagingandwrappingequipment,157pentosansin,93-94productiontechnology,149-157proteinsin,20-21,93saltin,39shorteningin,92-93,152,253,255-256stabilityoffoamsandemulsionsin,87-89starchin,94substitutionstrategiesin,265-268sugarin,34,152,252-253sugarsubstitutionin,265-266surface-activematerialsin,94-96,97surfactantsandemulsifiersin,41volumeexpansionof,184-185waterin,39water-solubleproteinsin,93wheatflourin,93-94See alsoBatter,cake

Calciumacidpyrophosphate,60Calorimeters,differentialscanning,194Campana,L.E.,227Canolaoil,136Cappedcolumntestdevice,195Caprenin,264Carbohydrate-basedfatmimetics,262-264Carbondioxide

chemicalleaveningand,51-54cookiebakingand,167doughandbatterreactionratesand,60-61qualityofsoftwheatproductsand,62-63

Carbonyls,66-67Cardiovasculardiseaseandsugar,249Carmelization,33,251-252,253Carrageenan,262-264Cartoningmachines,172Cassonmodel,100-101,111Celik,I.,207Celluloseandgums,262-264Chemicalleavening,50-54

blends,61-62Chemistry,food,49-50Chlorination,flour,22-24,103-104Cholesterol

fatsand,250

sugarand,249Christenson,M.E.,198,204,205,206Classification,wheat,2-3Clements,R.I.,19Cole,E.W.,19Cole,M.S.,40Color

Maillardreactionformationof,65wheat,3

Combinedtransportphenomenaduringbaking,180-184

Combustionmethod,10Condensationandinternalevaporation,179-180Conductiveheattransfer,175-176,177Conductivity,thermal,194-196,199-204,205-

206,213Consumerconsumptionofsweetgoods,246-247Continuousmixers,163Convectiveheattransfer,176Convectoradiantovens,168-169Cookiesandcookiedough

acrylamidein,71-72baking,165-170blendsofchemicalleaveningagentsin,61-62compression,123cooling,170dynamictest,124-126eggsin,37empiricalmeasurementmethods,122-123extensionalviscosity,126-127fatandfatreplacersin,35-36,132-139,253-

254,256fat-free,268fundamentalmeasurementmethods,123-127ingredients,127-143,144interrelationshipbetweenrheological

propertiesofdoughandcookiequality,145

lipidsin,19-20-makingandmixers,159-163microwave-baked,231modifiedpenetrometer,123-124nonfatdrymilkin,40packagingprocessandequipment,170-172penetration,123pentosansin,19processingandshaping,163-165production,159-172proteinsin,14-15,17-18,139-143,144rheologicalmethods,122-127shorteningin,167spread,18starchin,18-19,168substitutionstrategiesin,265-268sugarandsugarreplacersin,34,128-132,

168,253-254sugarsubstitutionin,266-267

52748.indb 276 2/6/08 2:28:02 PM


Index

testingequipment,12,14,122-123textureprofileanalysis,123transienttests,124waterin,127-128,167weakerproteinsin,14-15

Coolingcake,157cookies,170

Copelanddepositors,155-156Cornillon,P.,225Crackers,16,174Crank,J.,198Creamoftartar,57Creep,124,142Crestamachines,153,155Crumbandcrustdevelopment,185-186Cyclamate,258-259

dDamage,sprout,10-11Damagedstarch,11Datacompilationandpredictionmodels

specificheat,198-205thermalconductivity,199-204,205-206

Davies,C.G.A.,106Density,197-198,199-204,206-207Dentalcaries,247-249Depositors,155-156DeVries,U.,179Dextrins,262Diabetesandsugar,248Dicalciumphosphatedihydrate,59Dickerson,R.W.,196Dielectricproperties,225,226Dietaryfiber,106Differentialscanningcalorimeters(DSC),194,

195,208Diffusion,mass,178-179Diffusivity

moisture,198,199-204,207thermal,196-197,199-204,206

Diglycerides,83-84,95Dimagnesiumphosphate,60Direct-gas-firedovens,168Dispersionofshortening,90DisproportionationandOstwaldripening,89Dithioerythritol(DTE),143Doe,C.A.,24Donelson,J.R.,19,20,22,103Dosingeffectonrheology,113-114Double-actingbakingpowders,56Doughreactionrate,60-61Doughrheology

Alveographand,13-14,122-123extensographand,122-123MixographandFarinographand,14,122-123

Doughs

biscuit(SeeBiscuitsandbiscuitdough)cookie(SeeCookiesandcookiedough)yeasted

eggsin,36leaveningagentsin,38nonfatdrymilkin,40saltin,39sugarin,33waterin,38-39

Dumppackagingofcookies,171-172Dynamictests,124-126

eEdoura-Gaena,R.-B.,207Eggs

incakes,36-37,43,93incookies,37emulsifiersasreplacementfor,90-91functionsof,36-37rheologyeffectof,113inyeasteddoughs,36

Electric-firedovens,168Emulsifiedbakeryfat,134-135Emulsifiers,40-41

applicationincakeproduction,90-91dispersionofshorteningusing,90disproportionationandOstwaldripening,89emulsionformation,82-83asfatextenders,265filmrupture,89filmthinning,89hydrophilic-lipophilicbalanceand,85-87mixingtimereductionusing,90proteinmaterialas,85reducingfatandeggcontentusing,90-91rheologyeffectof,107-110solidparticlestabilization,88stability,87-89surfacechargesin,88-89typesandforms,83-85

Enzymes,42incakes,94-96,97surface-activematerialsgeneratedusing,

94-96,97Erythritol,261Evans,E.,249Evaporation

condensationandinternal,179-180onthesurfaceandmassconvection,180

Experimentalmilling,7Extensionalviscosity,126-127Extensographs,122-123

fFahloul,D.,185FallingNumberSystem,10

52748.indb 277 2/6/08 2:28:03 PM


Index

Farinographs,14,122-123Fats

-basedreplacers,264-265inbiscuits,36,135incakes,35,81-82,92-93,255-256carbohydrate-basedfatmimetics,262-264incookies,35-36,133,253-254,256functionsof,35-36,254-256obesityand,249-250reduction,44,90-91rheologyeffectof,104-107substitutionstrategies,262-265,267-268

Fermentationprocess,252Fiber,dietary,106Fick’slaw,178,183Fillingsandicings,254,256Film,emulsion

rupture,89thinning,89

Flavor,formationof,65-67,186Flour

alkalinewaterretentioncapacityof,11-12ashcontent,10break,4,8incakes,93-94,150-151chlorination,22-24,103-104componenteffectsoncookies,17-20damagedstarch,11doughrheology,13-14heat-treated,104milling,3-5moisture,10particlesize,20polyphenoloxidasein,11proteincontent,5,14-17,139-143,144qualityevaluationof,7,10-12rheologyeffectof,102-104softwheat,3,5-7solventretentioncapacityof,12sproutdamage,10-11

Foamcakemixing,152,253Foodchemistry,49-50Fructose,129,257-258,261Frye,A.M.,265

gGaines,C.S.,12,15,17,19,20,22,103,142-143Galatea,139-141Galdeano,M.C.,192,207Gallagher,E.,44Gasesinleavening,51Gekas,V.,198Gelatinization,6,34,96,168

microwavebakingand,228-229sugarfunctionin,252-253

Gelroth,J.,16Geometrycuttingtechnique,198

Gibbs-Marangonieffect,89Glucono-d-lactone,60Gluten

incookies,167kneadinganddevelopmentof,252rheologyand,139-143,144vitalwheat,42

Glycerolmonosterate(GMS),84-85,86,107-108,267

Goebel,N.K.,228Gomez,M.,43,207Gravity,specific,197Greer,E.N.,6Grigelmo-Miguel,N.,106Grossmann,M.V.E.,192,207Growth,wheat,3Guardedhotplatemethod,194-195Gujral,H.S.,109Gumsandcellulose,262-264Guy,R.C.E.,109

hHalogenlampheating,235,237-238Harper,J.C.,176Hayakawa,K.I.,198Hazen,S.P.,9,14Heat,specific,193-194,198-205Heattransfer

andcombinedtransportphenomenaduringbaking,180-184

conductive,175-176,177halogen-lamp,235,237-238impactduringbakingonproduct

characteristics,184-186jetimpingementoventechnology,216-223mechanismsduringbaking,174-178modelingandoptimizationof,186-188,192radiative,176,178

Heat-treatedflour,104Hicsasmaz,Z.,266High-ratiocakes,16,84,95-96,97,112-113,251Hodge,J.E.,63Horizontalmixers,153Hoseney,R.C.,18-19,34,111Hou,G.H.,18,21Huebner,F.R.,18Hwang,M.P.,198Hybridtechnologies,169

hybridjetimpingementandmicrowaveoven,232-235,236

microwave-infrared,235-238Hydrocolloids,42-43,116Hydrophilic-lipophilicbalance(HLB),85-87,

108Hydroxymethylfurfural(HMF),72-73,74-75Hyperactivityandsugar,249

52748.indb 278 2/6/08 2:28:03 PM


Index

IIcingsandfillings,254Impingingjets.SeeJetimpingementoven

technologyIndirectlyfiredforcedconvectionovens,169Infraredradiation,235-238Inglett,G.E.,137Ingredientsofsweetgoods

additives,40-43eggs,36-37fat,35-36leaveningagents,37-38nonfatdrymilk,40rheologyand,102-113,127-143,144salt,39studiesoneffectsof,43-44sugar,33-35,44,128-132water,38-39,127-128

InstronUniversalTestingMachine,123Intensesweeteners,258-259Interfacialrheology,88Interfacialtension,87-88Inulin,267,268Isomalt,260-261

jJanestad,H.,178Jetimpingementoventechnology,216-223

hybrid,232-235,236Johnson,A.C.,22-23Jyotsna,R.,41

KKennedy,S.C.,194,198,206Kerneltexture,9Keskin,S.O.,237Khouryieh,H.A.,106Kim,C.S.,41,106,112Kim,Y.R.,225Kissell,L.T.,19,22-23Kjeldahlmethod,10Knives,stripping,169-170Kocer,D.,44,266Kulacki,F.A.,194,198,206Kulp,K.,22,34

lLactitol,260Lamberg,I.,198Large-scalecakeproduction,157Larrea,M.A.,207L-cysteinhydrochloride(LCS),143Leaveningacids,56-60

blended,61-62Leaveningagents

bakingpowders,38,54-63chemical,50-54,61-62functionsof,37-38gasesactingin,51yeast,50-51

Lecigran,108Lee,L.,16Lee,S.,101,137Lewandowicz,G.,229Lignans,106Lind,I.,193Lipids

-basedemulsifiers,85incakes,21,94-96incookies,19-20flourchlorinationand,22-23insoftwheatflour,7

Locustbean,262-264

MMaache-Rezzoug,Z.,124Maillard,L.C.,63Maillardreaction,33,63-65,186,251-252,253

acrylamideformation,69-72antioxidantsformation,67-68colorformation,65flavorandaromacompoundsformation,

65-67,186hydroxymethylfurfuralformation,72-73,

74-75lossofnutritionalquality,68-69toxiccompoundsformation,69-73,74-75

Maltitol,260Maltodextrins,262,267Manohar,S.,41,124,128,135,143,145Marcotte,M.,198,207Margarine,134-135Marketingofsweetgoods,246-247Masoodi,F.A.,106Massconvection,180Massdiffusion,178-179Masstransfer

impactonproductcharacteristics,184-186mechanismsduringbaking,178-180modelingandoptimizationof,186-188

Matsuki,J.,21Measurement,thermophysicalproperties.See

ThermophysicalpropertiesMegahey,E.K.,231Meredith,R.J.,224Metaxas,A.C.,224Microparticulatedproteins,264Microwavebakingtechnologies,223-231

hybrid,232-235,236-infraredcombinationovens,235-238

Milk,nonfatdry,40Miller,R.A.,18-19,111

52748.indb 279 2/6/08 2:28:03 PM


0 Index

Milling,flour,3-5experimental,8

Mixingcakebatter,150-155cookiedough,162-163anddosingeffectsonrheology,113-114machines,153-155methodofmeasuringspecificheat,193-194timereduction,90,131-132

Mixographs,12,14,122-123,133Mizukoshi,M.,34,115-116Modelingandoptimizationofheatandmass

transfer,186-188,192Modifiedpenetrometers,123-124Modifiedstarches,262Mohsenin,N.N.,193Moisture

diffusivity,198,199-204,207flour,10lossduringbaking,185-186lossrateinjetimpingementovens,220-221

Monocalciumphosphate,58Monodomixcontinuousaerators,155Monoelectronicdepositors,156Monoglycerides,83-84

surface-active,94-96,97Monomultipurposemachines,153,155Morr,C.V.,207Morris,C.F.,19Mortonpressurewhisks,153-154Motwani,T.,225Murakami,E.G.,193

nNemeth,L.J.,14N-ethylmaleimide(NEMI),143Neural-network-basedequationsofthermal

conductivity,213Nix,G.H.,197Nonemulsifiedhydrogenatedfat,134-135Nonfatdrymilk,40Noodles,16-17Nutritionandnutritionalproblems

ofbakingpowders,61ofconsumptionoffatsandsugars,247-250offats,249-250,254-256functionsofsugarsandfatsinsweetgoods

and,251-256Maillardreactioneffecton,68-69substitutionstrategiesfor,257-268ofsugars,247-249,251-254

oOakescontinuousmixers,154,163Oatbran,106Oatrim,107

Obesityfatand,249-250sugarand,249

Ohlsson,T.,193Okos,M.R.,193Olestra,264-265Olewnik,M.C.,34Oligofructose,267Oligosaccharides,261Omega-3-fattyacids,106Osborne,T.B.,5Ostwaldripening,89Ovens,baking,168-170

jetimpingementtechnology,216-223microwave,223-231microwave-infraredcombination,235-238modelingofheatandmasstransferin,

187-188Oxidizingagents,40Ozmutlu,O.,230

PPackagingandwrappingequipment

cake,157cookie,170-172

Palav,T.,229Particlesize,flour,20Pasting,6Payne,P.I.,18Pectin,262-264Pedersen,L.,123,124,125-126,139,141-142,

145Penetrometers,modified,123-124Pentosans

incakes,93-94incookies,19insoftwheatflour,7

Polydextrose,44,261,267Polyglycerolesters(PGE),84Polyols,259-261Polyphenoloxidase,11Popkin,B.M.,250Potassiumbicarbonate,54Potassiumbromate,143Potassiumiodate,142-143Preston,K.R.,39Probemethodofmeasuringthermaldiffusivity,

197Processingandshaping,cookie,163-165Production

cake,149-157cookie,159-172jetimpingementoven,216-223wheat,2-3

Propyleneglycolmonostearate(PGMS),84Proteins

-basedfatmimetics,264

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Index

inbiscuits,143,144incakes,20-21,93incookies,14-15,17-18,139-143,144asemulsifiers,85flourchlorinationand,23-24microparticulated,264productsrequiringstronger,16-17productsrequiringweaker,14-16softwheatflour,5water-soluble,93wheatflour,10whey,264

Purawave®,238Pycnometers,197

rRadiativeheattransfer,176,178Raftiline,268Rahman,M.S.,196Ranhotra,G.,16Rao,H.,41,124,128,135,145Rapeseed,198Rapidheattransfertechnology,216RapidViscoAnalyzer,11Rask,C.,193Reactionrates,60-61Reciprocatingagitatormixers,163Reducingagents,40Reductionsystem,milling,4Reineccius,G.,227Replacers,fat,262-265Rheology

Alveographand,13-14ofcakebatters,102-116cookiedoughingredientsand,127-143,144effectofingredientson,102-113eggeffecton,113empiricalmeasurement,122-123emulsifierseffecton,107-110fatandfatreplacereffecton,104-107,

132-139floureffecton,102-104fundamentalmeasurementmethods,123-127hydrocolloidseffecton,110-113,116interfacial,88interrelationshipbetweenqualityofcookies

anddough,145methods,100-101,122-127mixinganddosingeffectson,113-114MixographandFarinograph,14,122-123sugareffecton,110,116,128-132temperatureeffecton,115-116textureprofileanalysis,123watereffecton,127-128

Rice,111Ritmo,139-141Rogers,D.E.,227

Ronda,F.,44,192,207,265Rosenthal,A.J.,266Rotary-moldeddoughs,160-161Rothstein,W.G.,250Rubio,A.R.I.,205Russo,J.V.,24

sSablani,S.S.,206Saccharin,258Sahi,S.S.,107,109Sahin,S.,122,123Sakonidou,E.P.,228Salt,functionsof,39Sanchez,C.,268Seetharaman,K.,229Seguchi,M.,21,23Setser,C.S.,265Sevimli,M.,237Seyhun,N.,231Shaping,cookie,163-165Shearer,A.E.H.,106Shelke,K.,42,102,103Shepherd,I.S.,115Shortening

incakes,92-93,152,253incookies,167creamingmethod,253dispersion,90rheologyeffectsof,107,136-139

Simplesse®,264,268Singh,R.P.,195Single-actingbakingpowders,56SingleKernalCharacterizationSystem(SKCS),9Sinha,N.K.,23Small-scalecakeproduction,156Sodiumacidpyrophosphate,58-59Sodiumaluminumphosphate,59Sodiumaluminumsulfate,58Sodiumbicarbonate,37,52-54Sodiumcarbonate,54Sodiummetabisulfite(SMS),141-142Sodiumsteroyllactate(SSL),108Softwheatflour,3,5-7

incookiesandbiscuits,121-122doughrheology,13-14lipidsin,7pentosansin,7proteinsin,5,14-17starchin,5strongerproteinsand,16-17weakerproteinsand,14-16

Soliddisplacementmethod,197-198Solidparticlestabilizationofemulsions,88Sollars,W.F.,23Solventretentioncapacity(SRC),12Souza,E.,18

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Index

Specificgravity,197Specificheat,193-194,198-205Specificvolume,199-204,206-207Spies,D.,34Spindlemixers,163Springwheat,3Sproutdamage,10-11Stability,emulsion,87-89Standing,C.N.,205Starch

incakes,94incookies,18-19,168damaged,11derivativesasfatreplacers,262flourchlorinationand,22hydrocolloidsand,42-43microwavebakingand,229insoftwheatflour,5-6

Steady-statetechniquesofmeasuringthermalconductivity,194-195

Steffe,J.F.,124Stephanmachines,153,155Steward,B.A.,6Strippingknives,169-170Strongerproteins,productsrequiring,16-17Substitutionstrategies

incakesandcookies,265-268fat,262-265,267-268sugar,257-268

Sucrose.SeeSugarSudha,M.L.,268Sugar

acrylamideformationand,71-72inbiscuits,35,128-129,130bloodglucoseand,248incakes,34,152,252-253cardiovasculardiseaseand,249incookies,34,128-132,168,253-254dentalcariesand,247-249diabetesand,248fructose,129,257-258,261functionsof,33-35,44,251-254hyperactivityand,249intensesweetenersasreplacementof,258-259microwavebakingand,230nutritionalproblemsofconsumptionof,

247-249obesityand,249replacers,257-258rheologyeffectof,110,116substitutionstrategies,257-268inyeasteddoughs,33,251-252

Sumnu,S.G.,122,123,207,225Sunfloweroil,134-135Surface

chargesinemulsions,88-89evaporationandmassconvection,180

Surface-activematerialsincakes,94-96,97Surfactants,40-41Sweat,V.E.,205,206Sweetgoods

additivesin,40-43consumerconsumptionof,246-247eggsin,36-37fatin,35-36,251-256functionsofsugarsandfatsin,251-256heattransferduringbaking,174-178impactofheatandmasstransferduring

bakingoncharacteristicsof,185-186ingredientsin,32-44,127-143,144leaveningagentsin,37-38marketingof,246-247masstransfermechanismsduringbaking,

178-180modelingandoptimizationofheatandmass

transferbakingof,186-188nonfatdrymilkin,40saltin,39sugarin,33-35,251-256tasteof,32-33varietiesof,2,32-33,173-174,192-193waterin,38-39

tTadano,T.,206Takeda,K.,21Tartaricacid,57-58Tasteofsweetgoods,32-33Temperature

effectonrheology,115-116history,196-197

Tempering,4Tension,interfacial,87-88Testweight,wheatgrain,8Texture

kernal,9profileanalysis,123wheat,3

Therdthai,N.,176,180Thermalconductivity,194-196,199-204,205-

206,213Thermaldiffusivity,196-197,199-204,206Thermophysicalproperties

datacompilationandpredictionmodels,198-207

density,197-198,199-204,206-207measurementtechniques,193-198moisturediffusivity,198,199-204,207specificheat,193-194,198-205theoreticalmodels,208thermalconductivity,194-196,199-204,

205-206,213thermaldiffusivity,196-197,199-204,206

Thorvaldsson,K.,178

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Index

Tonellimixingsystem,154Tou,K.,206Toxiccompounds

acrylamide,69-72hydroxymethylfurfural,72-73,74-75

Transfattyacids,250Transienttests,124,195-196Triglycerides,249Triticum aestivum,2Tsen,C.C.,23,41Turabi,E.,111Tweedymixers,153,155

uUriyo,M.B.,14Usage,wheat,2-3

vVarietiesofsweetgoods,2,32-33,173-174,

192-193Varriano-Marston,E.,22Verticalmixers,153Vetter,J.L.,35Viscosity

batter,62-63,95,99-100,106-107,108-109,116

extensional,126-127fateffectson,137-138

Vitalwheatgluten,42Volatilesalt.SeeAmmoniumbicarbonateVolume

expansion,184-185specific,199-204,206-207

WWalker,C.E.,41,112Wang,M.,7Water

absorption,42incookies,127-128,167functionsof,38-39holdingcapacityofsugars,252

Watson,E.L.,176Weakerproteins,productsrequiring,14-16Wheat

color,3growth,3production,classification,andusage,2-3texture,3

Wheatflour.SeeFlourWheatgrain

breakflouryield,7experimentalmilling,8kerneltexture,9qualityevaluationof,7-9testweight,8

Wheyprotein,264Whorton,C.,227Winterwheat,3Wire-cutmachines,164-165Wolraich,M.,249Wrappingandpackagingequipment,cake,157

xXanthangum,111-112,238,262-264Xylitol,129,260-261

yYamamoto,H.,14,17Yamazaki,W.T.,11,19Yasukawa,T.,116Yeasteddoughs

eggsin,36functionsofyeastin,251-252leaveningagentsin,38nonfatdrymilkin,40saltin,39sugarin,33,251-252surfactantsandemulsifiersin,40-41waterin,38-39

Yeastleavening,50-51Yoell,R.W.,115Yudkin,J.,249

zZanoni,B.,178,181,183Zhou,L.,195Zoulias,E.I.,129,266,268Zylema,B.J.,228

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52748.indb 284 2/6/08 2:28:05 PM


food engineering aspects of baking sweet goods

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