physicochemical, textural and viscoelastic properties of palm diacylglycerol bakery shortening...

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Research ArticleReceived: 22 April 2009 Revised: 21 March 2010 Accepted: 29 April 2010 Published online in Wiley Online Library: 26 July 2010

(wileyonlinelibrary.com) DOI 10.1002/jsfa.4088

Physicochemical, textural and viscoelasticproperties of palm diacylglycerol bakeryshortening during storageLing-Zhi Cheong,a Chin-Ping Tan,b Kamariah Long,c

Mohd Suria Affandi Yusoffd and Oi-Ming Laia,e∗

Abstract

BACKGROUND: Diacylglycerol (DAG), which has health-enhancing properties, is sometimes added to bakery shortening toproduce baked products with enhanced physical functionality. Nevertheless, the quantity present is often too little to exertany positive healthful effects. This research aimed to produce bakery shortenings containing significant amounts of palmdiacyglycerol (PDG). Physicochemical, textural and viscoelastic properties of the PDG bakery shortenings during 3 monthsstorage were evaluated and compared with those of commercial bakery shortening (CS).

RESULTS: PDG bakery shortenings (DS55, DS64 and DS73) had less significant increments in slip melting point (SMP), solid fatcontent (SFC) and hardness during storage as compared to CS. Unlike CS, melting behaviour and viscoelastic properties of PDGbakery shortenings remained unchanged during storage. As for polymorphic transformation, CS contained only β crystals after8 weeks of storage. PDG bakery shortenings managed to retard polymorphic transformation for up to 10 weeks of storage inDS55 and 12 weeks of storage in DS64 and DS73.

CONCLUSION: PDG bakery shortenings had similar if not better storage stability as compared to CS. This is mainly due tothe ability of DAG to retard polymorphic transformation from β ′ to β crystals. Thus, incorporation of DAG improved physicalfunctionality of bakery shortening.c© 2010 Society of Chemical Industry

Keywords: palm diacylglycerol; palm stearin; bakery shortening; physicochemical properties; textural properties; viscoelastic properties;storage properties

INTRODUCTIONShortening is a solid fat product which has been carefullyprocessed for functionality and to remove undesirable flavour andaroma.1 Until 1903 it was developed from lard; then a liquid-phasehydrogenation process was patented by Joseph Crossfield andSons for the production of shortening.2 Today, further innovationssuch as inter-esterification and physical blending have increasedthe ability of the industry to meet both specific functional andnutritional requirements.

Bakery shortening, when used for cakes, imparts a number ofdesirable functions including improving organoleptic properties,providing tenderness, texture and structural integrity, aiding inlubrication and incorporation of air and also extending shelflife.3 For optimum baking performance, bakery shortening shouldcontain a minimum of 20% solid fat content (SFC) at the workingtemperature (25 ◦C). In addition, it should also contain a minimumof 5% SFC at high temperature (40 ◦C) to aid in structural formationof cake.4 Besides that, β ′ crystals, which are effective in entrappingdispersed air for higher cake volume, are also essential in bakeryshortening.5

Monoacylglycerol (MAG) and/or diacylglycerol (DAG) are some-times added in small quantitities to bakery shortening to producecakes with enhanced physical functionality. Both MAG and DAG

possess marked surface activity due to their content of bothlipophilic and hydrophilic groups. Due to these properties, cakesbaked from bakery shortening with added MAG and or DAG usu-ally have softer crumbs, larger volume and longer shelf life.6 DAG,which is rich in unsaturation, has recently been found to possesshealthful values, such as in weight management,7,8 and post-prandial lipid reduction.9,10 Nevertheless, the amount of added

∗ Correspondence to: Oi-Ming Lai, Department of Bioprocess Technology, Facultyof Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, UPM,43400 Serdang, Selangor, Malaysia. E-mail: [email protected]

a Department of Bioprocess Technology, Faculty of Biotechnology and Biomolec-ular Sciences, Universiti Putra Malaysia, UPM, 43400 Serdang, Selangor,Malaysia

b Department of Food Technology, Faculty of Food Science and Technology,Universiti Putra Malaysia, UPM, 43400 Serdang, Selangor, Malaysia

c Malaysian Agricultural Research & Development Institute (MARDI), PO Box12301, 50774 Kuala Lumpur, Malaysia

d Sime Darby Research Sdn. Bhd., PO Box 207, 47200 Banting, Selangor, Malaysia

e InstituteofBioscience,Universiti PutraMalaysia,UPM,43400Serdang,Selangor,Malaysia

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Storage stability of palm diacylglycerol bakery shortening www.soci.org

DAG in bakery shortening is often too little to exert its healthfulvalue. It was not until the late twentieth century to the earlytwenty-first century that attempts were made to include DAG asone of the main components (more than 30% of total formula-tion) of bakery shortening to improve the nutritional properties ofbaked products.11

When developing shortening, careful consideration should begiven to storage stability. This is because storage may lead tochanges in physicochemical, textural and viscoelastic propertiesof shortening. This is especially true when palm stearin (PS) isemployed in the formulation of shortening as it is known tofrequently lead to problems of post-hardening during storage. Atpresent, literature on storage stability of DAG-enriched shorteningis limited. Thus, efforts should be made to further understand theeffect of DAG incorporation on storage stability of shortening.

This study aimed to produce bakery shortenings containingsignificant amounts of palm diacylglycerol (PDG) (at least 50%of total formulation). Physicochemical, textural and viscoelasticproperties of the PDG bakery shortenings were evaluated andcompared with those of commercial bakery shortening (CS). ThreePDG bakery shortenings were firstly developed from PDG andPS (IV44). They are known as shortenings DS55 (XPDG = 0.50,XPS = 0.50), DS64 (XPDG = 0.60, XPS = 0.40) and DS73(XPDG = 0.70, XPS = 0.30). Based on our previous work, PDGbakery shortenings produced from these formulations had highstructural complementarity, ideal mixing behaviour and alsocrystallisation in a mixture of β and β ′ forms (unpublished data).Thus, it is important to study the storage stability of these bakeryshortenings. PDG bakery shortenings produced and CS were storedat room temperature (25 ◦C) for a period of 3 months. Everyfortnight from the initial week after manufacturing till the finalweeks of storage, the physicochemical, textural and viscoelasticproperties of all the shortenings were analysed.

MATERIALS AND METHODSMaterialsPalm olein (POo) (IV 56) and PS (IV 44) were provided byGolden Jomalina Sdn. Bhd. (Tanjung Panglima Garang, Selangor,Malaysia). Commercial immobilised lipase from Rhizomucor miehei(Lipozyme RMIM) was obtained from Novozymes A/S (Bagsvaerd,Denmark). Commercial bakery shortening (CS) (Crisco, Pillsbury,US) was obtained from Giant Hypermarket (Petaling Jaya, Selangor,Malaysia). All chemicals and solvents used were either ofanalytical or high-performance liquid chromatography (HPLC)grade, respectively, and were obtained from Sigma-Aldrich (Sigma-Aldrich, Malaysia).

Sample preparationPDG were produced by partially hydrolysing POo using LipozymeRMIM in a 10 kg scale packed bed bioreactor and purified throughshort path distillation as described by Cheong et al.12 PDG bakeryshortenings were prepared according to the method describedby Danthine and Deroanne.13 PDG and PS IV44 at PDG molarfractions, XPDG = 0.5–0.7 were first heated to 60 ◦C and mixed for2 min by a motorised mechanical stirrer to ensure homogeneity.The mixtures were then crystallised for 30 min in a freezer at−20 ◦C. PDG bakery shortenings and CS were then stored inroom temperature (25 ◦C) for 3 months. Every fortnight from theinitial week after manufacturing till the final weeks of storage,the physicochemical, textural and viscoelastic properties of all thebakery shortenings were analysed.

Slip melting pointSMP for the PDG bakery shortenings and CS were determinedusing method described in the AOCS Method Cc 1–25.14 Duplicatemeasurements were obtained.

Solid-fat contentSFC for PDG bakery shortenings and CS were determined using aBruker Minispec mq 20 pulse nuclear magnetic resonance (pNMR)(Bruker Spectrospin Ltd, Coventry, United Kingdom). The sampleswere heated to 60 ◦C for 30 min, followed by chilling at 0 ◦C for90 min and then kept at the desired temperatures for 30 min priorto measurements. The melting, chilling and holding of the sampleswere carried out in pre-equilibrated thermostated baths. The SFCwere measured within the temperatures ranges from 0 ◦C to 60 ◦Cin 5 ◦C increments. Data were reported as the averages of twomeasurements.

Differential scanning calorimetryA Perkin-Elmer DSC-7 (Norwalk, CT) was used to analyse thethermal properties of the PDG bakery shortenings and CS. Samplesweighed between 6 and 10 mg and were sealed in aluminium pans.The prepared pans were firsy heated to 80 ◦C for 15 min to ensureno residual nuclei remained. To obtain the crystallisation curve, thesamples were cooled from melt (80 ◦C) at 5 ◦C min−1 to −60 ◦C. Toobtain the melting curve, the samples were equilibrated at −60 ◦Cfor 15 min before heating to 80 ◦C at 5 ◦C min−1. All samples wereanalysed in duplicate.

TextureHardness of the PDG bakery shortenings and CS were measuredusing a TA-XT2 texture analyser (Stable Micro Systems Ltd, Surrey,United Kingdom). The hardness values of the shortenings weremeasured at room temperature (25 ◦C) which was also the storagetemperature using a cone angle of 45 ◦C with a penetrationdepth of 5 mm and a penetration speed of 1 mm s−1. Doubledeterminations were performed.

ViscoelasticityViscoelasticity of PDG bakery shortenings and CS were determinedaccording to method described by Lai et al.15 using a Haake RS 100rheometer (Haake GmbH, Kalsruhe, Germany). The rheometer hasa stabilised low-inertia air bearing and also a high resolution digitalencorder. Temperature control of the rheometer was maintainedby a Haake F3 circulator waterbath with an accuracy of ±0.02 ◦C.First, each sample was carefully scooped out with a flat-basedplastic spatula to minimise sample deformation. It was thenconditioned to test temperatures (25 ◦C) before measurementswere taken. A parallel plate geometry (PP35) was used to performstress sweep at 1 Hz to determine the linear viscoelastic region(LVR). Small frequency sweeps from 0.01 to 100 Hz were thencarried out within the LVR to avoid destruction of the samples. Thevalues for the storage modulus (G′), loss modulus (G′′) and tan δ

were obtained. All samples were analysed in duplicate.

Fourier transform infrared analysisSubcell packing and polymorph of the PDG bakery shortenings andCS were determined using the Bruker Alpha FT-IR Spectrometeraccording to method described by Piska et al.16 The samples weresandwiched between the KBr windows and placed in the cellholder. The spectra were recorded with a total of 256 scans at a

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resolution of 16 cm−1. A single band appearing at the infrared CH2

rocking region r(CH2) of 721 cm−1 or the scissoring region δ(CH2)of 1467 cm−1 indicated the hexagonal subcell packing; hence, theα crystalline form. In the β ′ form (orthorhombic perpendicular),two bands were observed at the r(CH2) of 720 cm−1 and 726 cm−1

or the δ(CH2) of 1465 cm−1 and 1473 cm−1. As for β form, asingle band appearing at the r(CH2) of 717 cm−1 or the δ(CH2)of 1470 cm−1 indicating presence of triclinic parallel subcell.17,18

Duplicate measurements were obtained.

Statistical analysisThe data were subjected to analysis of variance (ANOVA) usingMinitab 12 statistical software (Minitab Inc, Pennsylvania, USA).The significance level being tested was α = 0.05. Differenceswith a significance level of 5% (P < 0.05) were considered to besignificant.

RESULTS AND DISCUSSIONSlip melting pointFigure 1 shows the changes in SMP of different shorteningsthroughout the storage period of 12 weeks. SMP for all theshortenings increased throughout the storage period with CShaving the highest overall increment (2.5 ◦C) followed by DS55(1.75 ◦C), DS64 (1.75 ◦C) and DS73 (1.0 ◦C). The reason for thehigh increment of SMP in CS is mainly due to transformationof fat crystals from the β ′ to the β form. Fat crystals in the β

form are able to align into large needle-like agglomerates whichresults in a stronger crystal network, hence, formation of a firmerproduct.19 PDG bakery shortenings, on the other hand, had lowerincrements of SMP due to the ability of PDG to delay polymorphictransformation from the β ′ to the β form. This is in accordancewith findings by Wright and Marangoni,20 and Siew and Ng,21 onthe ability of DAG to stabilise the metastable polymorphs in fats.

The Tukey paired comparison was used to examine thedifferences in SMP for all the shortenings during storage. Asidefrom DS73, all other shortenings (CS, DS55 and DS64) hadsignificant (P < 0.05) increments in SMP throughout the storageperiod. This indicates all the shortenings with the exception ofDS73 had undergone noteworthy polymorphic transformationfrom β ′ to β form during storage which resulted in formation ofa firmer products with significantly increased SMP. DS73, on theother hand, contained sufficient DAG which greatly delayed theundesirable polymorphic transformation. Hence, the insignificantSMP increment during storage.

Figure 1. Changes in SMP of PDG bakery shortenings (DS55, DS64 andDS73) and CS throughout the storage period of 12 weeks.

Solid-fat contentThe SFC profile gives an indication of the baking performanceof cake shortening. At the working temperature (25 ◦C), cakeshortening should contain a minimum of 20% SFC. In addition, itshould also contain a minimum of 5% SFC at high temperature(40 ◦C) to aid in the structural formation of cake.4 Changes of SFC atthese temperatures and body temperature (37 ◦C) during storageperiod are shown in Fig. 2. SFC for all the shortenings at 25, 37and 40 ◦C increased throughout the storage period. In accordancewith previously discussed findings on changes in SMP, CS alsoshown the highest overall increment in SFC during the storageperiod followed by DS55, DS64 and DS73.

A closer examination on changes in SFC for all the shorteningsthroughout the storage period shown CS had significant (P < 0.05)increment in SFC at all temperatures during both the earlyweeks (0–2 weeks) and the later weeks (10–12 weeks) of storage(Fig. 2D). Meanwhile, DS55 (Fig. 2A), DS64 (Fig. 2B) and DS73(Fig. 2C) had insignificant increments in SFC during the earlyweeks but significant (P < 0.05) increments in SFC during the lastweeks of storage. Increments in SFC during the storage period aredue to agglomeration of fat crystals into the β form. Significantincrements in SFC only during the later weeks of storage onceagain showed PDG delayed polymorphic transformation from theβ ′ to the β form.

Differential scanning calorimetryFigure 3 shows the melting curves of all the different shorten-ings throughout the storage period. Both DS55 (Fig. 3A) andDS64 (Fig. 3B) had very similar melting curves which remainedunchanged throughout the storage period. DS55 and DS64had three melting fractions: the low melting fraction (LMF)with one peak, the medium melting fraction (MMF) with twopeaks and the high melting fractions (HMF) also with twopeaks. In fact, the temperatures and endotherms for all thefive different melting peaks had no significant differences. Thus,storage had no effect on the melting behaviour of DS55 andDS64.

Melting curves for DS73 (Fig. 3C) too were similar throughoutthe storage weeks. The number of peaks remained unchangedduring the 12 weeks with one peak in LMF, another peak inMMF and two peaks in HMF. Though insignificant, there wasslight increment in the endotherm size in MMF. Temperaturesfor all the four melting peaks had no significant differences.Therefore, melting behaviour for DS73 too was unaffected bystorage. Figure 3D shows the melting curve of CS. CS had similarmelting behaviour with insignificant changes in melting peaktemperatures and endotherm sizes. Like all the PDG bakeryshortenings, storage had no effect on the melting behaviourof CS.

Hardness and viscoelasticityPlastic fats are three-dimensional networks consisting of solidfat crystals which are held together by primary (irreversible) andsecondary (reversible) bonds.15 Primary bonds which are theresult of fat-crystal agglomerates do not reform after rupture and,hence, are irreversible. Meanwhile, secondary bonds are able toreform back into the reversible van der Waals forces after beingruptured.22

Hardness which is a measure of the primary bonds impartsinformation on workability, functionality and oral properties ofcake shortening.23 Fig. 4 shows the changes in hardness of

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Figure 2. Changes in SFC of different shortenings at 25, 37 and 40 ◦C throughout the storage period of 12 weeks: (A) DS55, (B) DS64, (C) DS73 and (D) CS.Means for the different bar charts with different superscripts differ significantly (P < 0.05).

different shortenings throughout the storage period of 12 weeks.All shortenings had increased hardness at the end of the storageweeks with CS having the highest overall increment followedby DS55, DS64 and DS73. Nevertheless, increments in hardnessfor all the shortenings are insignificant. Hardness of PDG bakeryshortenings were found to increase in smaller extent as comparedto CS. This indicates PDG delayed agglomeration of fat crystals,hence, retarded crystals transformation from β ′ to β .

Viscoelasticity which reflects the secondary bonds (van derWaals forces) indicates the ability of fat samples to exhibitviscous flow behaviour, but also behaves somewhat as elasticsolids.24 Analysis of viscoelasticity and rheological properties of asample must be conducted under stress conditions in which thesample is at rest and in its actual structure. The linear viscoelasticregion (LVR) refers to the range of stress that can be appliedto a sample without causing deformation or destruction of thesample. In addition, LVR is also indicative of the intermolecularforces and structure of the sample.25 Thus, knowledge of theLVR of a sample is very important before performing analysis onviscoelasticity and rheological properties of sample. Stress sweepwas conducted to determine the LVR for all different shortenings.Table 1 shows the LVR values for all shortenings throughoutthe 12 week storage period. It is noteworthy that PDG bakeryshortenings had larger LVR values compared to CS. The largerLVR indicates PDG bakery shortenings had more elastic and firmerstructures as compared to commercial shortening. It is possiblethat PDG had increased the capability of the shortenings to beelongate without rupturing.

Viscoelasticity can be measured and expressed in terms of itsstorage and loss moduli. The storage modulus, G′, is a measureof elasticity, or energy stored, while the loss modulus, G′′, isa measure of viscosity, or energy lost. The ratio of the loss and

Table 1. LVR for PDG bakery shortenings (DS55, DS64 and DS73) andCS throughout the storage period of 12 weeks

Stress (Pa)

Time (weeks) DS55 DS64 DS73 CS

0 30–89 29–91 30–111 28–79

2 32–92 30–95 29–108 27–82

4 30–98 27–100 28–107 27–88

6 27–95 28–103 30–111 30–91

8 28–91 31–106 30–113 30–91

10 27–89 31–106 29–113 27–85

12 27–90 31–109 29–113 30–88

storage moduli is called the loss tangent which indicates whether asample is more solid-like or liquid-like:26 tan δ = G′′/G′. Frequencysweep within the LVR were performed to obtain values of G′,G′′ and tan δ. Values of G′, G′′ and tan δ are shown in Figs 5, 6and 7.

From Fig. 5, it can be seen that G′ increased with frequencyfor all storage weeks. G′′, on the other hand, decreased withfrequency for all storage weeks (Fig. 6). Both G′ and G′′ werefound to be frequency dependent, which is a typical solid-like behaviour.27 This phenomenon can be found in manyfood systems such as butter,24 shortenings,25 starch granules28

and processed cheese.29 Increasing G′ and decreasing G′′with frequency shows a transition from a more viscous toa more elastic food system. It is noteworthy that for alldifferent shortenings, the values of G′ were higher than thevalues of G′′ at any given frequency. Thus, values of tanδ were all below 1 (Fig. 7). High G′, low G′′ and tan δ


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Figure 3. DSC Melting curves of all different shortenings throughout the 12 weeks storage period: (A) DS55, (B) DS64, (C) DS73 and (D) CS.

values in shortenings indicate that the fat crystal aggregatesprevent translational movement; hence, the visoelastic solid-likebehaviour.27

The Tukey paired comparison was used to examine the dif-ferences in viscoelastic properties (mean for G′, G′′ and tan δ at1 Hz) of all shortenings during the 12 weeks storage. PDG bakeryshortenings with the exception of DS55 showed no significantdifferences in terms of values of G′, G′′ and tan δ throughoutthe storage period. This indicates storage has no effect on their

viscoelastic properties. DS55 and CS, on the other hand, hadsignificant (P < 0.05) increment in values of G′ and decre-ment (P < 0.05) in values G′′ during storage. This indicatesa higher degree of firmness in DS55 and CS which may dueto rearrangement of the fat crystals into a three-dimensionalscaffolding network upon storage. From the loose crystal chainforms, the crystal network may later be reinforced by strong pri-mary bonds during storage, resulting in the formation of hardersamples.23


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Figure 4. Changes in hardness of PDG bakery shortenings (DS55, DS64and DS73) and CS throughout the storage period of 12 weeks. Means forthe different bar chart with different superscripts differ (P < 0.05).

Fourier transform infrared analysisTable 2 shows the subcell packing and polymorphic forms ofall the different shortenings throughout the 12 week storage

period. Starting from 0 week until storage for 6 weeks, all theshortenings, be it CS or PDG bakery shortenings, had doublets inthe rocking r(CH2) region of 720 cm−1 and 726 cm−1 in additionto a single band in the scissoring δ(CH2) region of 1470 cm−1.These indicate that all the shortenings had a mixture of β ′ and β

crystals.After 8 weeks of storage, CS had only a single band in the

δ(CH2) region of 1470 cm−1. This indicates that CS had undergonepolymorphic transformation from a mixture of β ′ and β crystalsto only β crystals. This finding is in accordance with previouslydiscussed findings on SMP, SFC and hardness of CS during storage.Polymorphic transformation from a mixture of β ′ and β crystalsto only β crystals in CS resulted in formation of a firmer product,hence, the significant increment of SMP, SFC and hardness of theproduct during storage.

PDG bakery shortenings with the exception of DS55 wereable to retard polymorphic transformation up to 10 weeks.After 12 weeks of storage, all the PDG bakery shortenings toohad only a single band in the δ(CH2) region of 1470 cm−1;

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Figure 5. Storage moduli (G′) as a function of frequency (Hz) of all different shortenings throughout the storage period of 12 weeks: (A) DS55, (B) DS64,(C) DS73 and (D) CS.

Table 2. Subcell packing and polymorphic forms of all different shortenings throughout the storage period

Subcell packing Polymorphic form

Time (weeks) DS55 DS64 DS73 CS DS55 DS64 DS73 CS

0 O⊥ + T// O⊥ + T// O⊥ + T// O⊥ + T// β ′ + β β ′ + β β ′ + β β ′ + β




8 O⊥ + T// O⊥ + T// O⊥ + T// T// β ′ + β β ′ + β β ′ + β β

10 T// O⊥ + T// O⊥ + T// T// β β ′ + β β ′ + β β

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Figure 6. Loss moduli (G′′) as a function of frequency (Hz) of different shortenings throughout the storage period of 12 weeks: (A) DS55, (B) DS64, (C) DS73and (D) CS.

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Figure 7. tan δ as a function of frequency (Hz) of different shortenings throughout the storage period of 12 weeks: (A) DS55, (B) DS64, (C) DS73 and (D)CS.


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hence, only β crystals were present. It is noteworthy thatDS55 underwent polymorphic transformation slightly earlierthan the others PDG bakery shortening. After 10 weeks ofstorage, shortening DS55 had only β crystals. Thus, once againPDG is shown to be able to retard undesirable polymorphictransformation.

ACKNOWLEDGEMENTSThe authors gratefully acknowledge Mr Azmi and Ms MaryGoh from MARDI, Serdang; and Mr Govalan, Mr Ananthan, MrRadha Krishnan and Mr Vijay Krishnan from Golden Jomalina,Banting; and Ms Shahariza from Halal Product Research Institutefor their kind technical assistance. Financial support of thiswork by Sime Darby Research Sdn. Bhd. is also gratefullyacknowledged.

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