effects of convective and microwave roasting on the ... · cocoa beans are the basic raw material...

467

grasas y aceites,62(4),octubre-diciembre,467-478,2011,

issn:0017-3495doi:10.3989/gya.114910

1. INTRODUCTION

Cocoa beans are the basic raw material for theproductionofchocolateandotherchocolateproducts.To obtain these products, the seeds must besubjectedtoacomplicatedtechnologicalprocessinwhichoneofthekeystepsisroasting.

Awidelyusedmethodofroastingcocoabeansisconvectionroastingwhichisbasedonsubjectingtherawbeanstoaflowofhotairinthetemperaturerangebetween130-150°Cfor15–45min.(BelitzandGrosch,1999,Minifie1989,NebesnyandRutkowski,1998,fiwiechowski1996).

Theinfluenceofhightemperaturesonthebeanscontributestomanyphysicalandchemicalchangesthat significantly alter their properties. Roastingproduces the characteristic aroma of cocoa, thelossofwater,volatileacidsandtannincompounds,aswellasthedeepeningofthebrowncolorofthebeanandtheassuranceofitsmicrobiologicalpurity(Belitz and Grosch, 1999, Benz, 2002, Jinap et al.,1998,LeeSY.et al.,2001;Minifie1989,NebesnyandRutkowski,1998,Redgwellet al.,2003;fiwiechowski1996,TrojanowskaandTrojan1999).

Theliteraturereviewssuggestthatthesefeatureswerestudied taking intoaccount thegeneral impactofprocessparameterssuchastemperatureandtime.(Britoet al.,2000,2002,Jinapet al.,1998,NebesnyandRutkowski,1998),andonlyafewworks(Krysiaket al., 2003, Krysiak and Motyl-Patelska, 2005)analyzed how other, important process parameters,namelyrelativehumidityandairflowvelocity,shapedthesechanges.Theuseof increasedairhumidityintheroastingprocesshasabeneficialeffectonbeanproperties(eg,improvesthedegreeofsterilizationofthe material (Benz, 2002), color (Krysiak, 2006), orthefatcontentofcocoa(KrysiakandMotyl-Patelska,2005). However, in the literature, there is a lack ofinformationonhowtheincreasedhumidityofairwillaffect thepropertiesof themain ingredientofcocoabeans-namelycocoabutter.

Convection roasting of cocoa beans has anumberofdrawbacks.Oneof them is thatdue tothetraditionalwayofheatandenergytransfer,theheat treatment process takes too long. This may

RESUMEN

Efectos del tostado por convección y microondas sobre las propiedades físico-químicas de granos de cacao y de manteca de cacao extraída de ellos.

Granosdecacaode lavariedadCostadeMarfilsehansometido a tostado mediante convección y microondas. Sehaestudiadoelefectode lascondicionesde tostadosobrelosatributosfísico-químicosprincipales(contenidodeaguaygrasa,acideztotalyvolátil)delcacaoengranotostadoylaspropiedadesdelagrasaextraídadeestematerial(Acidez,ín-dicedesaponificación, índicedeperóxidos, índicedeyodo,índicederefracción,contenidodefracciónpolar,perfildeáci-dosgrasos,absorbanciadeunasoluciónal10%enhexano).Sehancomparadolascaracterísticasdelosgranosdecacaotostadosycrudosysus fracciones lipídicas.Los resultadosdelosanálisismostraronqueeltostadomedianteconveccióndurante35minutosa135°C,conuncaudaldeairede1,0ms-1yHRde0,45causólosmenorescambiosenlacalidaddegrasamientrasqueeltostadomediantemicroondaspromovióenmayormedidalaoxidacióndeloslípidosaunquelacalidaddelosgranosdecacaotostadofuemejor.

PALABRAS CLAVE: Convección – Granos de cacao – Manteca de cacao – Microondas – Propiedades físico-quí-micas – Tostado de granos de cacao.

SUMMARY

Effects of convective and microwave roasting on the physicochemical properties of cocoa beans and cocoa butter extracted from this material.

ThecocoabeansoftheIvoryCoastvarietywereconvectivelyandmicrowaveroasted.Theeffectsofroastingconditionsontheprincipalphysicochemicalattributes(waterandfatcontents,totalandvolatileacidity)ofroastedcocoabeansandthepropertiesoffat extracted from this material (acidity, saponification index,iodine index, peroxide value, light refraction coefficient, polarfractioncontent,andFattyAcidprofile,absorbancyof1and10%solution in hexane) were examined. The characteristics ofroasted and raw cocoa beans and their lipid fractions werecompared.Resultsofanalysesshowedthatconvectiveroastingfor35minat135°C,airflowrate1.0mxs21andrelativehumidityRHof0.45%causedtheleastadvancedchangesinfatqualitywhilemicrowaveroastingpromotedoxidationoflipidsalthoughthequalityofroastedcocoabeanswasthebest.

KEY-WORDS: Cocoa beans – Cocoa butter – Convective – Microwave – Physicochemical properties – Roasting of cocoa beans.

Effects of convective and microwave roasting on the physicochemical properties of cocoa beans and cocoa butter extracted from this material

ByW. Krysiak

InstituteofChemicalTechnologyofFood,FacultyofBiotechnologyandFoodSciences,TechnicalUniversityofLodz

90-924Lodz,4/10Stefanowskiegostreet,Polande-mail:[email protected]

468468 grasas y aceites, 62 (4), octubre-diciembre, 467-478, 2011, issn: 0017-3495, doi: 10.3989/gya.114910

W.KRYSIAK

contributetothelossofaroma, increasedbitternessof beans and appearance of odor coming from thepresenceof forexampleacrolein(resulting fromthedisintegrationoftheglyceridesinthefat)andcertainothersubstances (e.g.dimethylpyrazine)whichgiveanundesirable,burnedflavortothebeans(Bednarski,1986, fiwiechowski, 1996). The disadvantage ofthismethodofroastingisalsotheexistenceoflargetemperature differences (from 10 to 12°C) betweenthekernelandthehuskofcocoabeans,whichmaycontributetotheunevenprocessofroasting.

Anothermajordisadvantageofconvectionroastingof thewholebeans isasignificant transferofcocoabutterfromkerneltohusk.Thisphenomenonisverydisadvantageous mainly due to economic reasons,sincemasschocolateproductionusesonlythekerneland the husk is waste. So, a greater fat content inthekernelof thebeanwill result inbetterpropertiesof chocolate masses (Krysiak, and Motyl-Patelska,2005,NebesnyandRutkowski,1998).

Theabovestateddisadvantagesof convectionroasting of cocoa beans may also affect thepropertiesofthefatthatisthemaincomponentofcocoa beans. In the literature, information aboutthepropertiesofcocoabutterobtainedfromcocoabeansofdifferenttypes,comingfromdifferentregionsof the world, or subjected to different processingoperations can be found (fermentation, drying)(Chaiseri and Dimick, 1989, Foubert et al., 2004,Shamsuddin and Dimick, 1986, Shukla 1995),but data describing the properties of fat obtainedfromcocoabeansroastedindifferentconditionsisscarce(Asepet al.,2008).

The application of microwaves seems to be analternativemethodthatcaneliminatethedisadvantagesofconvectionroasting.Theuseofmicrowavesinthethermalprocessingoffoodcansignificantlyshortentheprocessandthegenerationofauniformheatcreatesconditionsformoreuniformtemperaturedistributioninthematerial(YoshidaandKajimoto,1994).

Thestudies,whichusedmicrowavesintheprocessofroastingcocoabeans,werecarriedoutin:Sweden(FaillonandMaloney,1976),Switzerland(SwissPat1985),Brazil(Fadiniet al.,1997),Malaysia(Ing-STM1990) among others. Research efforts taken in thisarea focusedmainlyon the technicalpossibilitiesoftheapplicationofmicrowavestoshortenprocesstimeand reduce the temperature of roasted beans, buttheyvirtuallyignoredissuesrelatedtothepropertiesofroastedbeans,whichareessentialforthequalityofthechocolateobtained.OnlytheworkscarriedoutbyEung-JungLeeandcoworker(Eung-Jung-Leeet al.,2000)orFadiniandcoworker, (Fadiniet al.,1997)relatetotheeffectsofmicrowavesontheformationofflavor.

In the literature, the allegations against themicrowavearethatduetotheheatgeneratedinsidethematerial,itispossiblethatunexpectedchemicaltransformationswill takeplace. In particular, itmayinfluence products containing fats, including cocoabutter.Foodswithahigh fatand lowwatercontentquicklyabsorbmicrowavesandareintenselyheated(YoshidaandKajimoto,1994).Therapidheatingof

productscontainingsignificantamountsoffatmayberelatedtoadversefactors,suchasself-oxidation.

Based on numerous literature data (Albi et al.,1997, Farag, 1994, Farag et al., 1997, Koło‡yn-Krajewska, 1992, Tan et al., 2001, Yoshida andKajimoto,1994,Yoshidaet al., 1995,YoshidaandTakagi,1997)relatingtotheinfluenceofmicrowaveenergyon fats in plantmaterials or extracted fromthem, it can concluded that the impact of thistype of heat treatment is always negative. Theobserved discrepancies may result from appliedmicrowave treatmentparameters (time, temperature,power, frequency), but also with the kind of materialundergoing the heating process, and whether thematerialwasspeciallypreparedpreviously(humidified,roasted, or having constituents that may affect thepropertiesoffattyingredientsremovedfromit).

Thepresentedworkwasundertakenduetothescarcityofstudiesdevotedtotheeffectsofdifferentroasting methods (convective, microwave) on thephysicochemicalattributesofroastedcocoabeansandthequalityoffatextractedfromthismaterial.

2. MATERIALS AND METHODS

Cocoabeans (the IvoryCoast variety) from theIvoryCoastwereseparatedpriortoroasting(Minifie,1989) and only the medium size beans with adiameterof18-24mmwerethermallyprocessed.

2.1. Cocoa bean roasting

Cocoabeansweresubjectedtoroasting in thefollowingways:

Convective in the following conditions

1.Airtemperature(T)of135°C,airflowrate(v)of 1.0m×s21, relative humidity (RH) of 0.4% (“dryair”),time(t)of35min,

2. T of 135°C, v of 1.0 m×s21, RH of 5.0%(“humidair”),tof45min,

3.Tof140°CandRHof0.35%(“dryair”),atvof0.5m×s21 for10min,andatvof1.0m×s21 for20min(anincreaseinairflowrateduringheating).

The convection roasting of the beans wascarried out in a tunnel with forced air flow andwithout recirculation. A detailed description of theequipment and methodology of measurements isgivenin(KrysiakandMotyl-Patelska,2003).

Microwave conditions

PowerM5700W,f52450MHz,timet512.5min.

ThemicrowaveroastingprocesswascarriedoutinaBoschmicrowaveoven(Germany).

Regardlessoftheroastingmethod,asingleheattreatment was applied to 200g portions of beansdistributed in a single layer. Roasting time wasdetermined by the required ~2% water content inthewholebean[NebesnyandRutkowski,1998].

469grasas y aceites, 62 (4), octubre-diciembre, 467-478, 2011, issn: 0017-3495, doi: 10.3989/gya.114910 469

EFFECTSOFCONvECTIvEANDMICROWAvEROASTINGONTHEPHYSICOCHEMICALPROPERTIESOFCOCOABEANSAND…

During the convection roasting process the airparameters were controlled (temperature, flow rateand humidity). The temperature measurements ofbothairandkernelofcocoabeansweremadeusingaYCYmetertypeYC-262withanNiCr-NiAl(Taiwan)measuring probe. The air velocity was measuredwithaconjugatedTHERM2285-2Bmeterwith9915S120by theAhlborn’s(Germany)measuringprobe.Relative humidity of the “dry” air was calculatedaccordingto(Stobi>ska et al.,2006).

The increased air humidity (RH 5 5.0%) wasobtained by placing saturated steam in the tunnelformedinthegenerator(KrysiakandMotyl-Patelska,2005). Relative humidity was measured using aconjugatedTHERM2285-2BmeterwithanFHA636-HR2byAhlborn’s(Germany)measuringprobe.

Thetemperatureinthemicrowaveroastedbeankernel was determined immediately after the endoftheprocess.ThemeterusedwasYCYtypeYC-262withanNiCr-NiAlmeasuringprobe.

Roasted beans were air cooled to attain atemperature of 25°C, and then stored at roomtemperature in sealed glass containers. Beanswereshelledbyhandandthekernelwascrushedusing a GM-1electric laboratory mill by ZBPP(Poland). In the fragmented bean (particle size0,2-0,9 mm): water and fat content, total andvolatileacidityweredetermined,andcocoabutterwas extracted. Extraction was carried out in theSoxtecTecator (Sweden) apparatus, according totheprocedure recommendedby themanufacturerforusingchocolateasasubstance,withpetroleumether(bp40to60°C)astheextractingsubstance.

2.2. Determination of physicochemical properties

Cocoa bean analysis

Water content of raw and roasted cocoa beansandofnibsandshellswasdeterminedaccordingtotherecommendedprocedure(SandovalandBarreiro,2002).Fatcontentinnibswasassayedaccordingtothe standard PN-A-88021:1971 (Krełowska-Kułas,1993). Total acidity was estimated according to thestandardPN-A-88024:1979(Krełowska-Kułas,1993)and volatile acidity according to Krełowska-Kułas(Krełowska-Kułas,1993).

Cocoa butter analysis

Characteristicnumbers(acid,saponification,iodine,peroxide)andtherefractiveindex,definingthequalityoffatweredeterminedaccordingtoacceptedstandardmethods. In addition, the softening temperature andtotal clarification of the solution temperature weredetermined(PN-A-88030:1998).

The viscosity of fats was determined with aBrookfieldEngineeringLaboratoriesCompanyINCtypeHADvIII1viscosimeter(USA).Measurementswere performed at 400.5°C in the SC4-27measurementvesselatashearspeedinthe5-60s21range(PN-A-88035:1998).

The determination of hardness was performedusing the penetrometric method with a Höplerpenetrometer(Germany)andDSC111penetrometerby Setaram (France). The assay procedures usedwerepublishedintheliterature(ChaiseriandDimick,1989).

Inaddition,todeterminethechangestakingplacein fats the following parameters were determined:amount and composition of the polar fraction, thedegreeoftransformationinthefattyacidsinthenon-polarfraction,theabsorptionof1%(E1%

1cm)solutionof the fat samples in hexane in Uv light, and theabsorptionof10%solutionofthesamplesinhexaneinvisiblelight.

Determination of the amount and compositionof the polar fraction was performed by columnchromatography. The Kieselgel 60 (70-230 mesh)silicagelwasused.Thenon-polarfractionwaselutedwithapetroleumether:diethylether(87:13)mixture,andthepolarfractionwithdiethylether.Determinationwas performed according to DGF StandardMethods,1991,C-III3b.Thecontentof tri-,di-andmonoacylglycerolsandfattyacidsinthepolarfractionofvariousfatswastestedbyhighperformancesizeexclusionchromatography(HPSEC)accordingtotheprocedurebyPawłowiczandDrozdowski(PawłowiczandDrozdowski1997).Theanalysiswasperformedon a variance 8500 chromatograph using a PLgelcolumnwithalengthof30cmand7.5mmdiameter,filledwithpolystyrene-divinylbenzenecopolymerwithaporesizeof500Åandgraindiameterof5mm.

Inordertodeterminethedegreeoftransformationoffattyacidsincocoabutter(relativeFAlossescausedbyheating)thefattyacidcompositionwasdeterminedinnon-polarfractions,whichcontainthermooxidativelyunchangedtriacylglycerols.Thefattyacidcompositionwas determined by gas chromatography. For thispurpose, the non-polar fraction was transformed intomethyl esters in accordance with PN EN ISO 5509(2000). The transesterification using KOH catalystmethodwasused.DeterminationwasperformedusingaPyeUnicamPU4550gaschromatographequippedwith a flame-ionization detector (FID) and a streamsplitter(90:1).Foresterseparationacapillarycolumnwith thesymbolDB-23,30m0.25mm,0.25mm(Jand W Sientific) was used. The temperature of theanalysiswas180°C.Injectoranddetectortemperatureswere250°C.Theretention timesandpercentagesofindividualfattyacidsweredeterminedusingaHewletPackard3392Aintegrator.

Ther absorption of a 1% solution of the fatsamplesinhexanewasmeasuredforwavelengthsof 233 and 270 nm. Measurements were takenon a Genesis Milton Roy Uv-vIS apparatus. ThedeterminationwasbasedontheworkofTynekandDrozdowski(Tyneket al.,2001).Colorchangewasmeasuredbydeterminingtheabsorptionofa10%(E10%

1cm)samplesolutioninhexane,invisiblelight.Thestudywasconductedatawavelengthof420nm(bandwidthforcarotenes).MeasurementsweretakenonaGenesisMiltonRoyUv-vISapparatus.The determination was based on the work ofMancini-Fihoetal.(Tyneket al.,2001).


W.KRYSIAK

Allevaluationswerecarriedoutintriplicate.Theresultsweresubjectedtovarianceanalysis(ANOvA)andtheDuncantest(DMRT).Statisticalsignificanceoftheresultswasdeterminedatp0.05.

3.RESULTS AND DISCUSSION

3.1. Roasting of cocoa beans

The selection of conditions such as roastingtemperature, flow velocity, relative humidity andthetypeofenergywasdependentonthefollowingtechnologicalandprocessconditions:

Atemperatureof130-150°Cwaschosenbecauseofthetypeofcocoabeans(IvoryCoast)usedinthestudiesandby thedesiredphysical andchemicalpropertiesobtainedafterroasting.

Flowvelocitywasincludedinthestudybecauseof previous research conducted by Krysiak andcoworkers (Krysiak et al., 2003), showing that thisparameter significantly influences the speed of theroasting process and this in turn translates intoquality of the roasted beans. However, the use ofavariableflowrateintheroastingprocessresultedfromtheanalysisoftheroastingcurves(Fig.1)andthetemperatureroastingcurves(Fig.2)andtheneed

R2 = 1R2 = 0,9991

R2 = 0,9995R2 = 0,993

0

0,2

0,4

0,6

0,8

1

1,2

0 10 20 30 40 50 60roasting time [min]

redu

ced

spec

ific

hum

idity

T=140°C, v=0.5m/s, RH=0.35% T=150°C, v=0.5m/s, RH=0.3%T=135°C, v=1.0m/s, RH=0.4% T=140°C, v=1.0m/s, RH=0.35%

Figure1Effectoftemperatureandairflowrateonthereducedspecifichumidity*ofcocoabeansduringroastingin“dry”air

*the reduced value of the specific air humidity was calculated by dividing of the current value of this quantity by its initial value

0

20

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60

80

100

120

140

160

0 10 20 30 40 50 60

roasting time [min]

Tem

pera

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insi

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ibs

[°C

]

T=135°C, v=1.0m/s, RH=0.4% T=150°C, v=0.5m/s, RH=0.3%

T=140°C, v=0.5m/s, RH=0.35% T=140°C, v=1.0m/s, RH=0.35%

Figure2Changesintemperatureinsidecocoanibsduringroastingofcocoabeansin“dry”air



toseehowtheseconditionsaffectthepropertiesofcocoabeansandthebutterderivedfromthem.

An analysis of the curves (Fig. 1 and 2) showsthat the lowest temperaturewasachievedbybeansroasted at 140°C at a flow velocity v 5 0.5mxs21,while when the bean was roasted at v51.0mxs21 the achieved temperature was virtually atsimilar levels regardless of which air temperaturewas used 2135 or 140°C. Taking that intoconsideration, the roasting conditions used were:air temperature T 5 140°C, flow velocity v 50.5mxs21 for a time t 5 10 min, and v51.0 mxs21,timet520min,atarelativehumidityRH50.35%.

The studies also included the impact of thethird parameter, ie the relative air humidity, sincethe literature data indicates that the use of airwith higher humidity promotes processes suchas the sterilization of beans (Benz, 2002, Finken,1996,Stobi>skaet al.,2006).Thistypeofthermalprocessing results in products with better qualityby reducing the possibility of oxidation reactions(Mujumdar,1995).

Microwave heating was used because of thedifferentwayofgeneratingheatinwhichtheprocessiscarriedoutatahighspeed(Fadiniet al.,1997,Mudgett, 1989). Furthermore, in previous studies(Stobi>skaet al.,2001)highmicrobiologicalpuritywas obtained for the cocoa beans roasted withmicrowaves.Inthepresentworkthemethodusedconsisted of microwave heating based on thecontinuousfeedingofmicrowaveswithapowerof700Wasamethodabletoachieveawatercontentof 2% in the kernel of the bean in a short period oftime(t512.5min)andatemperaturesimilar tothatnotedforconvectionroastedbeansinT5135°C,flowvelocityv51.0ms21, relativehumidityRH50.4%,timet535min(“dry”airconditions).

3.2. Influence of the roasting method on cocoa bean properties

Table1showstheresultsofcocoabeanqualityaccording to chosen methods, by convection andby microwaves. The inclusion of these results in

this study was necessary due to the subsequentinterpretation of the results of the analysis ofcocoabuttersextractedfromthebeansroastedbythesemethods.Adetaileddiscussionof theeffectof roasting conditions on the physicochemicalpropertiesoftheroastedbeansispresentinearlierstudies(Krysiak,2002,Krysiaket al.,2003).

SummarizingtheresultsoftheanalysisinTable1, it should be noted that among the proposedconvectionmethodsthereisnosinglemethodthatwould clearly be beneficial in its influence on thedesired characteristics of the bean (low total andvolatileacidity,highfatcontent in thekernel).Thisis due to the specific composition of cocoa beansand the complex changes taking place during theroasting process. In terms of the greatest loss oftotal and volatile acidity in the methods, the bestconvective conditions seem to be T 5 135°C,v51.0mxs21 at RH 5 0.4%. These parametersof the process, however, cause too much transferof fat from the kernel to the husk, at the level of5.0%, which is not desirable for technological andeconomic reasons. However, the greatest loss ofthiscomponentfromthekernelwasobservedwhenthebeans roastedatT5 140°C,with variableairvelocityand relativehumidityRH50.35%. In thismethodcomparativelyhighlevelsoftotalandvolatileacidity were obtained, which is also not beneficialfromthepointofviewofthetechnology.Research(Krysiak et al., 2003) shows that the roasting ofcocoa beans at 150°C, despite the shorter time,resultedinincreasedacidityoftheroastedbeans.

Theapplicationofairwithhigherhumidity(RH55.0%),despitecontributingtoreducingcocoabutterlosses,resultedinabeanwhichwascharacterizedbyhightotalandvolatileacidity.

The roasting of beans using microwavesallowedforaroastedbeanwiththemostfavorablephysicochemical properties in a relatively shortperiodof time, ie the lowestvaluesofvolatileandtotal acidity and the highest fat content. Suchcharacteristicsofthebeancomefromthefactthatthe heat was generated in a different way, and,consequently,forashortprocessingtime.

Table1 Selected physicochemical characteristics of cocoa beans roasted in different conditions

Roasting process

conditions

Water content[%]

Total acidity [°n/d.m..]

Volatile acidity[%acetic acid/d.m.]

Fat content [%/d.m.]

Whole bean Kernel Husk Kernel Kernel Kernel

Rawbean 5.200.03 4.550.05 12.400.06 14.590.7 0.120.005 59.040.08

CR1 2.010.02 1.970.04 4.940.06 9.670.5 0.070.003 56.200.05

CR2 2.050.05 1.750.03 5.660.07 14.220.6 0.110.006 57.690.04

CR3 1.97007 1.900.05 4.910.07 11.770.4 0.080.003 54.280.08

MR 2.020.06 1.780.02 5.760.4 7.790.7 0.050.006 58.30.05

CR1–convectivelyroastedbeanT5135°C,v51,0ms21,RH50,4%,t535minCR2–convectivelyroastedbeanT5135°C,v51,0ms21,RH55,0%,t560minCR3–convectivelyroastedbeanT5140°C,v50,5ms21,RH50,35%,t510min1T5140°C,v51,0ms21,RH50,35%,t520minMR–microwaveroastedbeanM5700W,t512,5min


W.KRYSIAK

3.3. Influence of the roasting methods on cocoa butter properties

Table 2 summarizes the results of the mainphysicochemicalpropertiesofcocoabuttersextractedfrom the kernels of raw and roasted cocoa beansusingconvectionandmicrowavemethods.

Theobtainedvaluesofthebasicqualityparametersof cocoa fat in most cases are within the limits laiddowninthestandards.Accordingtothe(PN-A-88113:1998)standardandtheliterature(ChaiseriandDimick,1989,Shukla1995) the free fattyacidcontent (FFA)expressedas%ofoleicacid is0,5-3,1; Iv5193.3-194.2g I2/100g;Sv5188-198mgKOH/g, refractionindexnD

40 (1,456-1,459)andasofteningtemperature(Ts529to33°C)andtheclarificationtemperature(Tc530to34°C).Theobtainedvaluesshowthatonlythesaponificationvalue(Sv)canberegardedastoolow,especiallyinthecaseofroastingbeansinT5135°C,v51.0mxs21,RH55.0%,t560min.andinmicrowaveroasting. In the first case it may be due to the longtimeintheairwithhigherhumidity(RH55.0%)andachievingakernelwithahigher temperature than inthecaseof theprocesscarriedout in“dry”airat thesametemperature(Fig.3).

Inthecaseoftheapplicationofmicrowavesthesechangesmaybedictatedbythehighertemperatureinthekernelofthebeanduetothedifferentwayofheatingthematerial(Albiet al.,1997).LoweringoftheSvvalueprobablycomesfromthedegradationof triacylglycerolsandchanges in free fattyacids.Also,Yoshidaet al.(Yoshidaet al.,1995)foundthatthetriacylglycerolspresentinsesameoilobtainedfrommicrowave roasted sesame seeds were slightlyhydrolyzed in random locations.A loweringof theleveloffreefattyacidswithincreasingtemperaturewasobservedbyOzdemirandcoworkers(Ozdemiret al.,2001).Accordingtothem,thisphenomenon

may be due to the reduced activity of hydrolyticenzymessuchaslipaseandperoxidase.

However it should be noted that the observedchanges in Sv are no greater than 0.5% whencompared to the minimum values given by thePN-A-88113:1998 standard and other literaturedata(ChaiseriandDimick,1989,Shukla,1995).

TheIvsoftheanalyzedfatsarewithin29.4-37.0gI2/100gfat.ThelowestIvvalues(29.4and31.9gI2/kg), which are well below the value given by thePN-A-88113:1998 standard and the literature data(Chaiseri and Dimick, 1989, Shukla 1995), werethe characteristics of the fat from beans subject tothemicrowaveroastingmethodandrawbeans.Forthe other cocoa butters, the values were within therangeof34,6-37,02g I2/100g, thus thevalueswereconsistentwiththecitedliteraturereferences(ChaiseriandDimick,1989,Shukla,1995,PN-A-88113:1998).

Iv is a convenient indicator of the degree ofhardness of cocoa butter. Higher values of Iv ofcocoa butter (35,4-37,0 g I2/100g) indicate a highercontent of unsaturated fatty acids included in thetriacylglycerols. In the case of cocoa butter, theseacidsareresponsibleformostofitssoftness(ChaiseriandDimick,1989).Thisisconfirmedbythehardnessresultsobtainedbythepenetrometermeasurementsshown inTable2.Theonlyexception is the lackofcorrelation between the Iv and the hardness offat obtained from the microwave roasted beans.In this case the lowest Iv values and the highestvalues of hardness were observed. This may bedue to thegenerationof high temperatureswithintheheatedmaterial inashort time,whichcausesunforeseen changes in the fatty acids includedin the triacylglycerols. Similar relationships wereobservedbyAlbiandcoworkers(Albiet al.,1997)duringthemicrowaveheatingofvegetableoil.

Table2 Physicochemical characteristics of fat extracted from cocoa beans roasted in different conditions

Determined factorSource of fat

(1) (2) (3) (4) (5)

FFA[%oleicacid] 0.990.04 1.060.05 1.070.04 1.000.06 1.100.07

Sv[mgKOH/g] 187.00.5 192.61.05 182.31.10 187.01.01 183.10.95

Pv[mmolO2/kg] 1.30.05 2.10.10 2.30.07 1.40.05 2.00.09

Iv[gI2/100g] 31.90.9 34.60.6 35.70.5 37.00.7 29.41.5

nD40 1.4570.0005 1.4570.0005 1.4560.0005 1.4580.0005 1.4550.0005

Hardness[op] 0.250.005 0.460.005 0.480.005 0.610.005 0.620.005

viscosity[mPas] 25.50.5 39.490.5 32.950.5 34.000.5 38.00.5

Softeningpoint[°C] 27.70.5 31.50.5 30.10.5 30.50.5 31.80.5

Clarificationpoint[°C] 33.50.5 32.90.5 33.10.5 31.90.5 33.40.5

(1)-cocoabutterextractedfromrawbeankernel(2)-cocoabutterextractedfromconvectivelyroastedbeankernelT5135°C,v51,0ms21,RH50,4%,t535min(3)-cocoabutterextractedfromconvectivelyroastedbeankernelT5135°C,v51,0ms21,RH55,0%,t560min(4)-cocoabutterextractedfromconvectivelyroastedbeankernelT5140°C,v50,5ms21,RH50,35%,t510min1T5140°C,v51,0ms21,RH50,35%,t520min(5)-cocoabutterextractedfrommicrowaveroastedbeankernelM5700W,t512,5min



However,given thestatisticalevaluationof theresults it isconcluded that themethodof roastinghasasignificantimpactontheIv.

Theperoxide valuesweredetermined to be inthe1.3-2.3mmolO2/kgfatrange.

Together with Tan and coworkers [Tan et al.,2001]many researchersbelieve that thePv levelabove3.5mmolO2/kgfatisanunsatisfactorylevelduetoitssensoryproperties.

The lowest Pv was the characteristics of fatextractedfromrawcocoabeans(1)(Table1).Oomahand coworkers (Oomah et al., 1998) determined alowerPvinthefatfromunprocessedgrapeseedsthaninfatfromseedssubjectedtoathermaltreatment.

TheprocessofroastingincreasedthePv.Tothelowestdegree,onlyslightlyover7%(Pv51.4mmolO2/kgfat)theincreaseofthisvaluewasobservedforcocoabutter(4)(Table2)thatwasextractedfrombeansroastedbyconvectionatT5140°C,butwiththeuseofvariableairflowvelocity.SuchachangeinthePvmaybeduetothemilderconditionsusedinroastingtimeup to10minutes(Fig.2)andoverallshorter (t530min)timeoftheheatingmediumoperation.Itmayalsobe the antioxidant effects of products formed duringtheheatingofbiologicalmaterial,e.g.asaresultoftheMaillardreaction(Tyneket al.,2001)ForothervariantsofroastingthePvwasfoundtobeintherangeof2,0-2,3mmolO2/kgfat.TherelativelylowvalueofPv(Pv52.0mmolO2/kgfat)forcocoabutterextractedfrommicrowaveroastedbeanscanbecausedbyadifferentmethodofheating thebean,shortprocess time(t512.5min),andsimilarlyas inroastingatT5140°C,thepresenceof antioxidant substances in the cocoabutter.Tanandcoworkers (Tanet al., 2001)believethatthereasonsforlowvaluesofPvinsoyandcornoilsheatedbymicrowaveforupto12minutestimecan

befoundintheformationofhydroxyperoxidesatlowertemperatures. However, longer heating increasesthe temperature, which contributes to the rapiddecompositionofthehydroxyperoxidestosecondary,labile products, which can transform into productssuchasalcohols,aldehydes,ketones,acids,dimers,trimers,polymersandcycliccompounds.Thismaybeconfirmedbytheresultoftheadsorptionof1%solutionofsamplesinhexane(Table5).

The least favorable in terms of obtaining thehighest Pv of cocoa butter was the method ofconvection roasting of beans in air with higherhumidity(RH55.0%).Suchpropertiesoffatmaybe due to a long time (t 5 60min) of T 5 135°Ctemperature operation, but also the influence ofmoisture contained in the air heating the bean.Yoshida and coworkers (Yoshida et al., 1995)showedthatthefatpropertiesmaydependonthemoisture content contained in it. Increased watercontent in the material subjected then to thermaltreatment contributes to the formation of smallerquantitiesofbronzesubstances,whichsignificantlyinfluencethenatureofoxidativechangesinfat.

In thecaseof theFFAcontent the lowest value(FFA50.99%)isthecharacteristicsoffatfromrawbeans,while theFFAcontentof fatsextracted frombeans roasted by various methods was determinedtobewithin the limitsof1,06-1,10%. In thecaseofbeansroastedbyconvection(cocoabutters2,3and4)(Table2)thevaluesofFFAwererespectively1.06,1.07and1.0%.HigherFFAvalueswhencomparedtofatfromrawbeanscanbeassociatedwithorganicacidsremaininginthekernelofcocoabeans,whicharethenpassedtotheextractedfat(Table1).

The highest values of FFA 5 1.10% wereobservedforcocoabutter(5)(Table2)meaningthe

60

80

100

120

140

0 10 20 30 40 50 60 70

Roasting time [min]

Tem

pera

ture

insi

de n

ibs

[°C

]

RH=0.4% RH=5.0%

Figure3Changesintemperatureinsidecocoanibsduringroastingin“dry”and“humid”airasafunctionoftime

(Tof135°candvof1.0mxs21)


W.KRYSIAK

beansroastedbymicrowaves.SimilarrelationshipsintheirresearchwerefoundbyAlbiandcoworkers(Albiet al.,1997)andYoshida(Yoshidaet al,1995).

No significant changes in the values of therefractiveindex(n40

D51.4551.458)werefoundinthecocoabutterobtainedfromroastedbeansinrelation to the fat extracted from raw beans. Thelowest observed n40

D values (1.455) for the fatextracted from beans heated by microwaves canbe attributed to the generation of relatively hightemperaturesintheproductwithinashorttime.

The viscosity of fats extracted from heat-treatedbeans increases significantly, almost doubles, inrelation to the viscosity of crude fat from beans. Nosignificantdifferencesinviscosityvaluesbetweenbeanroasting methods were found. Similar relationshipswereobservedbyAlbiandcoworker(Albiet al.,1997)andOomahandcoworker(Oomahet al.,1998).Theincrease in the value of this quality parameter of fatmaybelinkedtotheformationofdimersorpolymersasa result of lengthening the carbon chains (Albiet al.,1997)orasdifferencesinsaturationoffattyacids(Oomahet al.1998).This, in turn,maytranslate intohigher softening point temperatures, as observedin the analyzed cocoa butter (Table 2). However,the temperature readout based on the conductedthermographic studies (DSC) showed no significantdifferencesbetweenthefatobtainedfromrawbeans

and beans roasted by microwaves (Fig. 4). AlsoChaiseriandDimick.(ChaiseriandDimick,1989)havenotacquiredagoodcorrelationbetweenthehardnessdeterminedbypenetrometerandbyDSC.

The obtained results have not allowed toexplicitly specify the influence of roasting methodontheactualchangesoccurringinthecocoabuttercontained in cocoa beans. Therefore, to estimatechangesintheextractedcocoabuttersthecontentofpolar fraction,compositionof thepolar fraction,and the degree of transformation of fatty acids inthenon-polarfractionweredetermined.

Determination of amount and composition of the polar fraction

TheamountandcompositionofthepolarfractionofcocoabutterextractedfromthekernelsofcocoabeansroastedbyvariousmethodsisshowninTable3.

The determinations show that the polar fractioncontent in relation to starting fat increased slightlydue to heating. Taking into account the statisticalevaluation of the results, differences are not foundin thecontentof thepolar fractionbetween trials2,3, 4. The fat (5) contains about 1% more of thisfractionthanotherfats,whichmeansthatthefathasundergone the biggest changes, in relation to theothersamples.Polarfractioninaccordancewiththe

Figure4DSCthermogramsoffatextractedfromrawandmicrowaveheatedcocoabeans

Temperature/ °C25 30 35 40 45 50

Heat Flow/ mW

-29

-24

-19

-14

-9

-4

Exo

Tm : 32.08 °CEnthalpy / J/g : 38.3478

M=700W

Raw cacao butterTm : 31.28 °C

Enthalpy / J/g : 11.6908



presented in Table 4, in the tested fats, takinginto account the losses of FA, generally speakingthermooxidative changes are at a very low level.These changes influenced mainly polyene acids(the loss of C18:2 is 11,1-13,4% for fat samples3 and 5, while the loss of C18:3, 51.9 and55.6% respectively). However, given the startinglow levels of these acids in the raw materialsubjectedto thermal treatment thesechangesdonot significantly affect the quality factors of thetestedfat.SimilarrelationshipswereobservedbyConssignani and coworkers (Conssignani et al.,1998).

Higher amounts of palmitic acid determined intheheatedfatsamplesisassumedtobeanaturalphenomenon, due to the fact that fats containingshorter chain acids hydrolyze easier than theones containing longer chains. This is confirmedby experiments by Farag and coworkers (Faraget al., 1997) who determined varying (increasingor decreasing) amounts of palmitic acid usingmicrowave heated olive oil when compared tosamplesnotsubjecttoheating.

Determination of the absorption level of 1% and 10% solution of fat samples in hexane

Changes in the absorption of 1% solutions ofanalyzed samples of fat (E1%

1cm) at λ5233 and270 nm determine the content of secondaryoxidationproductsinfats,especiallythosecontainingaldehydes and ketones (Tynek et al., 2001). DatacontainedinTable5indicaterelativelysmallchanges,which confirm previous conclusions on changes infattyacidsinthetestedsamplessubjectedtoheating.However, most oxidation products were observedin the sample of fat (4), meaning fat obtained frombeanstreatedwithconvectiveheatingatthehighestoftheproposedtemperatures.

In this respect the most preferred methodseems to be the roasting of beans in the air withhigher relative humidity. It is associated with thedemonstrated lower oxidation of products heatedinhumidair.Watervapor inair formsaprotective

legislation intheEuropeanUnion is thedeterminantof thermooxidative transformations of fats. Forexample, edible, commercially available refined oilscontain the polar fraction at a level of 3-4%, whilefryingfatiswithdrawnfromcirculation(friedfoodbars)afterexceedingthepolarfractioncontentof25-27%.Basedonthisdatait isclearthatthemajorityoftheanalyzedfatonlyslightlyexceedsthelevelof4%.

Slightdifferenceswerenotedinthecompositionofthepolarfractionoftheexaminedfats.Prioritizingaccording to the rule: from the largest to thesmallestdegreeofchange, the tested fatscanbecategorizedaccordingtothefollowingsequence:

ForTAGdimmercontent4521,4and5nodimers,

ForoxidatedTAGcontent........54321,ForDAGcontent..................54321,ForMAGcontent.................554515253,ForFAcontent............................53241

An analysis of individual components showsthat the greatest changes took place in fat (5)obtainedfromthebeansroastedbythecontinuousmicrowaving method, although not even traceamounts of dimers were found in it. The amountof diacylglycerols (DAG) describes the degree ofhydrolysis. Therefore, the degree of hydrolysis ofthetestedfatsissortedintheorderdescribedabovefortheDAGfraction.Itshouldbenoted,however,thatlikeintheworkofConssignaniandcoworkers(Conssignani et al., 1998) the quantity of polarfractionandcontentofitsindividualcomponentsinthesamplesissmallandclosetothevaluesfoundinrawfat.Inthislisttheworstpropertiesareshownforthefatfrommicrowaveroastedbeans.

Determination of the progress of fatty acid transformations

Inordertodeterminethedegreeoftransformationoffattyacidsintheheatedsamplesofcocoabutter,the fatty acid composition was determined in thenon-polar fraction, which contains thermooxidativelyunchanged triacylglycerols. As shown by the data

Table3 Composition of polar fraction of fat extracted from cocoa beans roasted in different conditions

Source of cocoa butter

Polar fraction amount [%]

Polar fraction composition [%]TAG dimers oxidated TAG DAG MAG FA

(1) 3.00.2 0.000.00 1.540.08 1.020.01 0.030.01 0.410.01

(2) 4.00.3 0.040.01 1.770.12 1.170.03 0.030.01 1.000.07

(3) 4.30.1 0.000.00 1.830.11 1.350.01 0.020.01 1.090.05

(4) 4.20.2 0.040.01 2.080.15 1.480.06 0.03001 0.570.01

(5) 5.50.1 0.000.00 2.390.23 1.730.11 0.030.01 1.350.10



W.KRYSIAK

Table4Fatty acid composition of fat extracted from cocoa beans roasted in different conditions

Fatty acid(1) (2) (3) (4) (5)

FA content [%]

14:0 0.12 0.09 0.10 0.09 0.09

15:0 0.02 0.03 0.03 0.03 0.02

16:0 24.37 24.59 23.13 24.56 24.18

16:1(9c) 0.25 0.23 0.22 0.22 0.22

17:0 0.22 0.22 0.22 0.21 0.21

17:1 0.02 0.02 0.01 0.03 0.01

18:0 33.85 34.04 33.59 33.82 33.51

18:1(9c) 33.50 32.56 32.31 32.67 32.25

18:2(9c,12c) 3.06 2.76 2.72 2.77 2.65

18:3(9t,12t,15t) 0.02 0.02 0.02 0.02 0.01

18:3(9c,12c,15c) 0.27 0.15 0.12 0.15 0.11

20:0 0.93 0.95 0.93 0.96 0.95

20:1(9c) 0.06 0.05 0.05 0.07 0.05

21:0 0.03 0.01 0.01 0.03 0.02

22:0 0.19 0.18 0.16 0.17 0.17

OtherFA 0.08 0.04 0.06 0.01 0.05


Table5Absorbance of 1% and 10% hexane solutions of fat extracted from cocoa beans

roasted in different conditions

Source of cocoa butterAbsorption of 1% butter sample at Absorption of 10%

butter sample atl 420nm [E10%

420]l 233nm [E1%

233] l 270nm [E1%270]

(1) 1.230(0.050) 0.01nomaximum 0.141(0.013)

(2) 1.401(0.132) 0.246(0.016) 0.225(0.026)

(3) 1.257(0.016) 0.222(0.013) 0.122(0.001)

(4) 1.433(0.088) 0.354(0.013) 0.164(0.001)

(5) 1.280(0.065) 0.255(0.053) 0.220(0.015)


layer that prevents the penetration of oxygen(Mujumdar,1995,Tynek et al.,2001).

Also Albi and coworkers (Albi et al., 1997) intheirstudiesonvegetableoilsheatedbyconvectionand microwave methods obtained an increase in(E1%

1cm)valueatλ5233and270nm.

Theobtainedresultsdonotshowagoodcorrelationwith the resultsofPv (Table2).Thus, this indicatesthe need for additional determinations of factors infats because the Pv cannot be the sole criterion fordeterminingthedegreeofchangesinfat,assuggestedbysomeresearchers(Tyneket al.,2001).



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The determined changes in color (E10%1cm) of

the fat samples indicate that in each case of fatheating there was a reduction in carotinoids, thelowest for sample (3). This characteristic changein color indicates the positive effect of moisturecontained in air with higher humidity on slowingthe reaction of the formation of brown products.SimilarrelationshipswereobtainedbyYoshidaandcoworkers(Yoshida et al.,1995)andYoshidaandTakagi(YoshidaandTakagi1997)forthemicrowaveheatingofsoybeansandsesameseeds.

For fat (2) and (5) an increase in the value of(E1%

1cm)indicatorwasseen,whichisrelatedtotherateofremovingwater frombeansandthestronginfluenceoftheMaillardreactiononthemagnitudeofthisparameter(Tyneket al.,2001).

4. CONCLUSIONS

The present results show that microwavesfavorably affected the physicochemical propertiesof cocoa beans. After a time of 12.5 min thelargest reduction in the total and volatile acidityof the beans was obtained, and fat has migratedfrom the kernel to the husk in the lowest degree.However,thefatextractedfromthebeansroastedthis way underwent the greatest changes. This isindicated by the fundamental values of indicatorsof the quality of fat (FFA, Pv, Iv, melting point),andbydetailedanalysessuchastheamountandcomposition of the polar fraction, the degree ofchange in fatty acids, or (E1%

1cm) at λ 5 233 and270nmand(E10%

1cm)values.Among the convective methods preferred in

scopeof theanalyzedphysicochemicalpropertiesof beans and the properties of cocoa butter isroasting T 5 135ºC in “dry” air. In terms of thefat remaining in the kernel of cocoa beans themost favorable was the method of roasting in airwith higher humidity, however, too long a heattreatment adversely affected the properties of thefatextractedfromthebean.

ACKNOWLEDGEMENT

TheauthorsthankthePolishMinistryofEducationand Science for its financial support (Grant No. 5P06G02319)ofthisresearch.

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effects of convective and microwave roasting on the ... · cocoa beans are the basic raw material...

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