Food Research International 69 (2015) 72–79

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Food Research International

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Quality characteristics of egg-reduced pound cakes following WPI andemulsifier incorporation

A. Paraskevopoulou a,⁎, S. Donsouzi a, C.V. Nikiforidis b, V. Kiosseoglou a

a Laboratory of Food Chemistry and Technology, School of Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greeceb Food Process Engineering, Wageningen University, P.O. Box 17, 6700АА, Wageningen, The Netherlands

⁎ Corresponding author. Tel.: +30 2 31 0 997832; fax:E-mail address: adparask@chem.auth.gr (V. Kiosseoglo

http://dx.doi.org/10.1016/j.foodres.2014.12.0180963-9969/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 9 October 2014Received in revised form 21 November 2014Accepted 14 December 2014Available online 20 December 2014

Keywords:egg substitutioncakewhey protein isolateHPMCSSLmicrostructure

The effect of partial (50 wt%) or total liquid egg replacement by whey proteins in combination withemulsifiers, i.e. hydroxypropylmethylcellulose (HPMC) and sodium stearoyl-2-lactylate (SSL), on the qual-ity of pound cakes was investigated. Cakes containing whey protein isolate (WPI) solutions of varying con-centrations (i.e. 20, 17 and 14% w/v) were first prepared. Complete egg replacement by WPI led to thepreparation of cake batter of increased specific gravity as well as to final cake products of inferior qualitywith regard to volume, texture and hardness increase upon storage, compared to the control. In the caseof partial liquid egg replacement byWPI solutions, cakes with acceptable sensory and quality characteristicswere obtained, which were further improved following the addition of emulsifiers. During a storage periodof four days the egg-reduced cakes exhibited a significantly lower staling rate depending mainly on theconcentration of WPI and the presence of emulsifiers. Finally, the analysis of cake microstructure confirmedthe positive effect of the co-addition of whey proteins and emulsifiers in egg-reduced cakes. This workmade it possible to develop an alternative, egg-reduced cake of satisfactory quality, by using a combinationof whey proteins with two common baking additives.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Cakes are baked products highly appreciated by the consumersworldwide, being characterised by a dense, tender crumb and sweettaste. Their quality mostly depends on ingredients used in the recipe,i.e. wheat flour, eggs, sugar, fat or oil and leavening agents, as well ason conditions prevailing during their preparation (e.g. mixing, baking).In addition to contributing to cake colour and aroma, eggs impartmoist-ness and provide a soft texture to the finished product due to their ex-cellent emulsifying, foaming and gelation properties (Conforti, 2014).Depending on the type of cake, either whole egg or only egg white isused. Madeira-type and yellow layer cakes are typical examples of fatcontaining cakes where egg proteins, mainly yolk lipoproteins emulsifythe fat during the ingredient mixing stage. In fat-free cakes, such asangel food or sponge cakes, egg proteins perform both aerating, i.e.assist in entrapping large air quantities, and coagulation/gelationfunctions during the preparation of the product (Kiosseoglou &Paraskevopoulou, 2014; Shepherd & Yoell, 1976).

Regardless of the number of functions performed by egg proteins inimproving cakes’ organoleptic quality, the current trend is to reduce theegg content or to replace eggs in these products in order to diminish thetotal production cost and also satisfy consumers with specific dietary

+30 231 0 997779, 997847.u).

restrictions or needs (people with high cholesterol or of various reli-gious beliefs, vegetarians, etc.). However, partial or total egg replace-ment can lead to unfavourable consequences regarding cake flavour,volume and texture. To achieve an acceptable quality, substantial mod-ifications of the recipe, i.e. use of either proteins from different sourcesor additives, is required. To this direction, satisfactory results havebeen obtained by using bovine blood plasma to replace whole egg oregg whites at various levels (Johnson, Havel, & Hoseney, 1979; Lee,Johnson, Love, & Johnson, 1991; Lee, Love, & Johnson, 1993). In theirstudy, Lee et al. (1991) observed that the use of fresh, frozen andspray-dried plasma to replace similar forms of egg whites in high-ratio white layer cakes resulted in cakes with similar volume, textureand appearance. Other authors have studied the impact of egg substitu-tion by plant protein materials (e.g. soy flour, lupine flour) on the bak-ing, texture and sensory characteristics of cakes. For example,Arozarena, Bertholo, Empis, Bunger, and Sousa (2001) investigated thepossibility of the development of an egg-free cake, using lupine proteinsand baking additives (baking powder, soy lecithin, xanthan gum,mono-and diglycerides), while in their study Abdul Hussain and Al-Oulabi(2009) reported the possibility of substituting the egg in the cake recipeby whey protein concentrate and lupine proteins. Their results showedsignificant differences between the control and the egg-substitutedcake with respect to the volume of the final products. More recently,Salem and Ahmed Hanan (2012), who examined the partial substitu-tion of eggs by lupine flour and protein isolate in cake preparation,

Table 1Cake formulations studied.

Ingredients Cake batter compositiona (g/320 g batter)

Α Β1 Β1a Β2 Β2a Β3 Β3a C

Sugar 80 80 80 80 80 80 80 80Margarine 80 80 80 80 80 80 80 80Whole egg 80 40 40 40 40 40 40 -Self-rising flour 80 80 80 80 80 80 80 80Aqueous WPI solution - 40 40 40 40 40 40 80HPMCb 0.4 - 0.4 - 0.4 - 0.4 -SSL solutionb 0.4 - 0.4 - 0.4 - 0.4 -

a fresh eggs, A (control); eggs -WPI solution (20%w/v)mixture, B1; eggs -WPI solution(20% w/v) mixture & emulsifiers, B1a; eggs -WPI solution (17% w/v) mixture, B2; eggs-WPI solution (17% w/v) mixture & emulsifiers, B2a; eggs -WPI solution (14% w/v) mix-ture, B3; eggs -WPI solution (14% w/v) mixture & emulsifiers, B3a; WPI solution (20%w/v), C.

b Emulsifier content (0.5 wt%) was calculated on a wheat flour basis.

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suggested that the cakes obtained by substituting 25% of eggs with 5%lupine flour or 2% protein isolate were highly acceptable. Additionally,the comparison of angel food cakes made from egg white or whey pro-tein foams revealed that egg replacement by whey proteins in angelfood cake battermay result in the formulation of cakeswith low volumeand coarse structure (Arunepanlop, Morr, Karleskind, & Laye, 1996;Berry, Yang, & Foegeding, 2009; Pernell, Luck, Foegeding, & Daubert,2002; Yang& Foegeding, 2010). Cake batters based onwhey protein iso-late exhibited lack of stability during the stage of transformation from awet foam to dry one, while the appearance of large bubbles was ob-served even at 22 °C (i.e. prior to heating). On the other hand, in cakebatters based on egg white foams a stable foam network was observedwhen heating from 25 to 85 °C (Berry et al., 2009).

Furthermore, some attempts have been made regarding the use ofhydrocolloids and emulsifiers to partially or totally replace egg incakes. According to Miller and Hoseney (1993), addition of xanthangum in the batter formulation contributed to the preparation of cakeswith similar or better characteristics than those of the control cakes. Inanother work, Ashwini, Jyotsna, and Indrani (2009) determined the ef-fect of a great variety of additives, i.e. gum arabic, guar gum, xanthangum, carrageenan, hydroxypropylmethylcellulose in combination withglycerol monostearate (GMS) and sodium stearoyl-2-lactylate (SSL),on the rheological, microstructural and quality characteristics of egglesscakes. Among the additives, HPMC appeared to be the best as it aided inthe preparation of good quality eggless cake either alone or in the pres-ence of GMS and SSL.

In the presentwork the possibility of partial or total egg reduction inpound cakes was investigated. To this direction, the liquid whole eggwas gradually replaced with whey protein isolate solutions at variouslevels and the quality characteristics along with the microstructureand storage ability of the resulting cakes were studied. In addition, theeffect of emulsifiers, namely HPMC and SSL, on the egg reduced cakeswas investigated in an attempt to improve their quality characteristics.

2. Materials and Methods

2.1. Materials

Self-risingwheatflour (moisture 11%w/w) (Jotis S.A., Greece), sugar(Hellenic Sugar Industry S.A., Greece), margarine (Vitam, Unilever S.A.,Greece) and fresh eggs (Tsakiris S.A., Greece) were purchased fromthe local market. Whey protein isolate (natural, unflavoured, lecithincontent b 3%) frombovinemilk, containing approximately 98% drymat-ter of which 91% was protein, was supplied by Nestlé (Germany). Com-mercially available food grade hydroxypropylmethylcellulose (HPMC)(HARKE Group, Germany) and sodium stearoyl-2-lactylate (SSL)(Alinda-Velco S.A., Greece) were used in the study.

2.2. Preparation of protein solution

A 20% (w/v)WPI solutionwasfirst prepared under continuousmag-netic agitation for 24 h, which was then suitably diluted with water,when needed, to obtain whey protein solutions of 17% and 14% (w/v)concentrations.

2.3. Cake preparation

Pound cakeswere prepared according to the following recipe:wheatflour (80 g), margarine (80 g), sugar (80 g) and liquid whole eggs ormixtures of egg-WPI solutions (1:1) or WPI solution (80 g) (Table 1)(Matsakidou, Blekas, & Paraskevopoulou, 2010). Margarine and sugarwere first mixed for 5 min at 500 rpm in a household electric mixer(23 °C). The rest of the ingredients were then incorporated under con-stantmixing for 5min. After flour addition, themixing processwas con-tinued for 2 more minutes. All ingredients had been previouslyequilibrated to room temperature for 30 min. Two hundred and twenty

five grams (225 g) of cake batter were then transferred into 5 ceramiccylindrical ramekins (5 cm height × 3.5 cm i.d.) and baked at 175 °Cfor 45 min. After baking, the cakes were removed from the ramekinsand left to cool at room temperature for 30 min. Then, they werewrapped in transparent film to prevent drying and stored at room tem-perature for either 24 h or a longer time (4 days). At least three sets of 5cakes per type of batter were prepared.

Whenever included in the formulation, SSL (in gel form) and HPMCwere added during the steps of fat-sugar mixing or flour addition, re-spectively. SSL gel was prepared by mixing the emulsifier and water ata ratio of 1:4, heating the dispersion at 45 °C under continuous stirringand cooling. For all the experiments the SSL or the HPMC content was0.5 % on a wheat flour basis.

2.4. Evaluation of cake quality characteristics

Batter specific gravitywas calculated by dividing theweight of batterby that of an equal volume of distilled water. Cake batter viscosity mea-surements were performed using the Brookfield viscometer model DVII(USA) equipped with concentric cylinder geometry at shear rate0.132 sec−1 using the small size adapter (SC4-25/13R) after a 15 minageing period at 25 °C.

Cake quality parameters included consumer acceptance, volume,baking loss, crumb features and texture of crumb. A preliminary sensoryevaluation of cakes was conducted with 40 volunteer panellists of21–57 years of age from staff, undergraduate and postgraduate studentsfrom School of Chemistry in Thessaloniki (Greece). All the panellists,who were regular cake consumers, were asked to evaluate the sampleson the basis of acceptance of cake appearance, aroma, taste, texture andoverall liking on a five-point hedonic scale (1= very disliked, 5 = veryliked) one day after baking. Three coded quarters, i.e. i) control cake, ii)cake where liquid whole eggs were partially replaced by WPI solutionand iii) cake where eggs were totally replaced by WPI solution, wereserved in a randomized order at room temperature. The panellistswere asked to rinse their mouth with water between sample evalua-tions. Cakes were considered acceptable if their mean scores for overallacceptance were above 3 (neither like nor dislike). The volume of cakeswas determined immediately after baking by the rapeseed displace-ment method. Baking loss (BL) was determined by weighing cakes24 h after baking and using the following equation (Rodríguez-García,Salvador, & Hernando, 2014):

BL %ð Þ ¼ B–Cð Þ=IW½ � � 100

where BL is the weight loss during baking, B is the weight (in grams) ofbatter before baking, C the weight (in grams) of cake after baking andIW is the initial water content (in grams). For the calculation of theIW content, the initial water of each ingredient in each formulationwas taken into account.

Table 2Effect of egg replacement on sensory characteristics of cakes.

Sensory attributes Cake batter prepared with a

A B1 C

Appearance 4.22c b 3.75b 2.19aAroma 4.36c 3.72b 2.62aTaste 4.53c 3.89b 2.54aTexture 4.53c 3.75b 2.49aOverall quality score (20) 17.64c 15.11b 9.84a

a eggs, A (control); eggs -WPI solution (20%w/v)mixture, B1; WPI solution (20% w/v),C.

b Values in the same row followed by different letters are significantly different (p b

0.05).

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Cake crumb characterisation included the calculation of thenumber of cells per cm2 and the ratio of cell area to total area(Paraskevopoulou, Provatidou, Tsotsiou, & Kiosseoglou, 2010;Skendi, Biliaderis, Papageorgiou, & Izydorczyk, 2010). For this pur-pose, at least three slices per cake type (20 mm thick) were scannedwith a scanner (Canon MP160). Image analysis was then performedon subimages (30 × 30 mm) taken from the centre of the sampleby using the UTHSCSA ImageTool programme (Version 2.0, Universi-ty of Texas Health Science Centre, San Antonio, Texas). A singlesquare of the crumb area was considered for each image.

Texture profile analysis was performed using a TA-XT2 textureanalyser (Stable Microsystems, UK) equipped with a 100 mm-diameter aluminium plate. Measurements were carried out at certaintime intervals of 0, 1, 2 and 4 days on cylindrical cake samples (3.5 cmdiameter × 2 cm height), after the removal of the upper part (crust).Each sample was subjected to a double cycle of compression underthe following conditions: crosshead speed 0.5 mm/s and compressiondistance 50% of cake’s height. The data were analysed by using TextureExpert software (v. 1.11) to measure hardness, cohesiveness, springi-ness and chewiness, as described by Bourne (2002). In addition to eval-uation of texture, the mechanical properties of cake samples weredetermined by converting the force–time curves into compressionstress [G(t)] – Hencky strain (εH) ones and employing the followingequations (Van Vliet, 1999): The stress G(t) was calculated from

G tð Þ ¼ F tð ÞA tð Þ

where F(t) is the compression force and A(t) is the actual surface area ofthe test sample at time t (assuming that the volume of the sample doesnot change during the compression and its shape remains cylindrical),given by

A tð Þ ¼ L oð ÞL tð Þ A oð Þ

where L(o) is the original sample height, L(t) is the sample height after acompression time t and A(o) is the initial compression surface area ofthe cake sample. The Hencky strain εH was calculated from

εH ¼ lnL tð ÞL oð Þ

2.5. Cryo-Scanning Electron Microscopy (Cryo-SEM)

Small pieces of cakes (2×3 mm) were cut from the center areawith a lancet. The pieces were glued on a brass sample holder withcarbon glue (Leit- C, Neubauer Chemicalien, Germany) and subse-quently freezed with liquid nitrogen. All manipulations were carriedout under liquid nitrogen. The sample holder was fitted in the trans-fer cryogenic Leica holder and transferred to a non-dedicated cryo-preparation system (MED 020/VCT 100, Leica, Vienna, Austria) ontoa sample stage at−93 °C. In this cryo-preparation chamber, the sam-ples were immediately freeze-dried for 23 min at −93 °C at 1.3 x10−6 mbar to remove contaminating water vapour. The samplewas then sputter coated with a layer of 4 nm Tungsten at the sametemperature. The samples were transferred cryo-shielded into thefield emission scanning microscope (Magellan 400, FEI, Eindhoven,the Netherlands) onto the sample stage at −122 °C at 4 x10−7 mbar. The analysis was performed with SE at 2 kV, 13 pA. Allimages were recorded digitally.

2.6. Statistical analysis

Statistical analysis of the data was carried out using SPSS (edition17.0) software package. Comparisons among means of samples were

carried by ANOVA (Analysis of Variance) using the Duncan’s multiplerange test. Significant differences among mean values were consideredat p b 0.05.

3. Results and Discussion

3.1. Preliminary sensory evaluation

The effect of partial or total egg replacement by WPI solution(20% w/v) on pound cakes sensory characteristics is presented inTable 2. As can be seen, an increase in the percentage of egg substitu-tion from 50 to 100wt% resulted in the decrease in the sensory scoresof all attributes. This is also reflected in the decrease in the overallquality score, i.e. the control cakes prepared with eggs received thehighest score (17.64) followed by the cakes prepared with egg-WPIsolution mixture (15.11), while the cakes prepared with WPIsolution received the lowest one (9.84) (p b 0.05).

3.2. Batter and cake physical measurements

The effect of liquid whole egg replacement with WPI solution onbatter specific gravity and cake volume, baking loss and crumb charac-teristics, is presented in Table 3. Specific gravity is a measure of thetotal air holding capacity, i.e. high values indicate less air incorporation,while low values indicate that more air bubbles have been incorporatedinto the batter. The specific gravity of control batter was 0.949, whichfollowing incorporation of WPI solution at a concentration rangingfrom 20 to 14% w/v was either not significantly affected (p N 0.05) (inthe case of 20 and 17% w/v addition) or increased slightly (in the caseof 14% w/v addition). The highest specific gravity value (0.975) wasobtained when the liquid egg was totally replaced by WPI solution,indicating a heavier batter that lacks proper aeration. In order to obtaina desirable final cake structure, the preparation of a batter entrapping alarge number of air bubbles is required. The air bubbles are producedduring the first stage of cake making, i.e. mixing of the cake ingredientsto obtain an aerated dispersion system with the water constituting thecontinuous phase in which the fat and the flour are dispersed. Theentrapped bubbles then move into the water phase where they startto act as nuclei and grow in size as a result of the gas generated due tothe leavening action of the baking powder and the increase in vaporpressure with temperature inside the bubbles. According to Shepherdand Yoell (1976), at this initial stage of cake making all the air is heldin the fat phase. Air entrapment and subsequent bubble stabilizationagainst coalescence, drainage and/or disproportionation are functionsmainly performed by the egg white proteins, while egg yolk proteincomponents appear also to assist in aeration and foaming (low-densitylipovitellenins) as well as in retention of air whipped into the system(high-density lipovitellins) (Graham & Kamat, 1977; Kamat, Lawrence,Hart, & Yoell, 1973; Kiosseoglou & Paraskevopoulou, 2014). In the caseof egg-reduced cake batter, whey proteins may antagonize the whitealbumin proteins leading eventually to their expulsion from theinterface. In their studies, Berry et al. (2009) and Yang, Berry, and

Table 3Physical and crumb morphological characteristicsa of batter and pound cakes.

Cake sampleb Batter density Volume(cm3)

Baking loss(% w/w)

Number of cells/cm2 Cell area/Total area

A 0.949 ± 0.013 a,b 105.58 ± 5.48 d 34.40 ± 1.21 d 109 ± 3 d 0.211 ± 0.012 cB1 0.947 ± 0.013 a,b 101.21 ± 0.77 c 31.23 ± 0.80 b 90 ± 5 b 0.202 ± 0.025 bB1a 0.952 ± 0.007 a,b 105.15 ± 2.59 d 31.46 ± 0.99 b 115 ± 5 d 0.216 ± 0.029 cB2 0.957 ± 0.001 b,c 101.61 ± 3.58 c 32.91 ± 0.53 c 88 ± 4 b 0.201 ± 0.032 bB2a 0.963 ± 0.003 b,c 101.13 ± 3.91 c 32.64 ± 0.49 c 82 ± 4 b 0.200 ± 0.021 bB3 0.970 ± 0.001 c 98.09 ± 1.62 b 32.44 ± 0.84 c 99 ± 2 c 0.205 ± 0.023 bB3a 0.971 ± 0.003 c 99.76 ± 0.93 b,c 32.10 ± 0.61 c 110 ± 1 d 0.212 ± 0.010 cC 0.975 ± 0.002 d 96.35 ± 0.65 a 28.04 ± 0.76 a 73 ± 3 a 0.160 ± 0.017 a

a Means ± standard deviation of at least three replicates. Values in the same column followed by different letters are significantly different (p b 0.05).b For sample codes see Table 1.

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Foegeding (2009) have reported that the more surface active wheyproteins dominate the air-water interface when used in admixturewith egg white leading to a decrease in the elasticity of the surface film.

As was expected, a relationship between the volume of air incor-porated during mixing and cake volume was observed, i.e. the lowerbatter specific gravity the higher cake volume (Table 3). Baking ofthe control batter led to aerated structure exhibiting a significantlyhigher volume (~106 cm3) when compared with that of the egg-reduced cakes. The volume was significantly decreased when liquidwhole egg were either partially (~101 cm3) or totally (~96 cm3)replaced by WPI solution (p b 0.05). This was probably due to bettergas retention capacity of the control batter as well as to a more con-trolled structure development during baking. In WPI-incorporatingcakes the decrease in expansion could be related to the decrease inbatter stability during baking, caused by structure change and possi-ble batter viscosity decrease (Arunepanlop et al., 1996; Ashwiniet al., 2009; Lakshminarayan, Rathinam, & KrishnaRau, 2006). Aswas shown by preliminary viscosity measurement experiments con-ducted in our lab, the viscosity values for the control batter and thosecontaining the 20 and 14%WPI solutions were 780, 675 and 530 Pa∙s,respectively. According to Sahi and Alava (2003), the final volume ofthe cakes does not only depend on the initial air incorporated in thebatter but also on its capacity to retain air during baking. In addition,as it has been reported by several researchers, the final cake struc-ture is based on gluten development as well as starch gelatinizationand egg protein denaturation (Wilderjans, Luyts, Brijs, & Delcour,2013; Wilderjans, Luyts, Goesaert, Brijs, & Delcour, 2010;Wilderjans, Pareyt, Goesaert, Brijs, & Delcour, 2008). Egg proteinsperform both as emulsifiers and foaming agents right from thebeginning of the process of cake preparation and cake batter forma-tion. In addition, protein denaturation during the intermediate andmainly during the final baking stage aid in the consolidation of thefinal cake structure, along with gluten structure development andstarch gelatinization and amylose release (Kiosseoglou &Paraskevopoulou, 2014; Wilderjans et al., 2013). Taking also intoaccount that air bubble expansion, combined with continuousphase viscosity reduction during the intermediate baking process,may impose a significant strain on the foam system leading to airescape and collapse (Kiosseoglou & Paraskevopoulou, 2014), it ap-pears that whey proteins have a lower ability to prevent the collapseof cake structure during baking although they have satisfactoryfoaming properties (Davis & Foegeding, 2007; Yang et al., 2009).Cakes having a lower volume have been also obtained when eggwhite was replaced by whey protein (Arunepanlop et al., 1996;Pernell et al., 2002), while Pernell et al. (2002) observed that angelfood cake batters containing whey proteins became less elasticthan traditional batters containing egg white at baking temperaturesfrom 60 to 85 °C and the resulting heat-set gel network structure wasnot able to prevent collapse once starch gelatinization began.

The addition of the emulsifier mixture into the WPI-incorporatingproducts did not result in any significant improvement in batter densityand cake volume except for the case of using the 20% (w/v)WPI solution

(B1a) where a cake volume similar to that of the control was recorded(105 cm3). Data for cake coded C are not shown, since not even a slightsignificant improvement was observed following emulsifier incorpora-tion. Bearing in mind that a cake batter represents a complex emulsionand foam system which is processed by being heat set, it should bepostulated that the higher total protein content alongwith the presenceof emulsifier assisted in air incorporation and fat dispersion in smallerparticles providing the needed number of air cells in the batter.

Image analysis of the crumb revealed that the ratio of total cell areato total area and the number of cells per cm2 of the control sample (0.21and 109, respectively) was significantly higher in comparison withthose of the egg-reduced cakes (Table 3). This indicates that WPI influ-enced the crumb characteristics in the way that cells were less in num-ber and covered a smaller area. The lowest values for both the averagecell area/total area (0.160) and the number of cells/cm2 (73) wereobserved in the case of total egg substitution (sample C). On the otherhand, in the case of 50% egg replacement, the above parameters weresignificantly higher than those of sample C and varied within a smallrange (0.201-0.205 and 88–99 cells/cm2, respectively), while the effectof decreasing WPI solution concentration on both parameters did notfollow any consistent pattern. This is probably the result of the inferiorair retention capacity of these systems. In general, a porous structureis associated with a softer, lighter crumb and thus with a higher sensoryquality (Morr, Hoffmann, & Buchheim, 2003). In the presence of emulsi-fiers, both parameters increased andwere similar to those of the control(p N 0.05). As can be observed, the resulting crumbs (B1a and B3a) had asimilar appearance compared with that of the control cake (Fig. 1).

As regards baking losses, the water retention capacity was affectedby the replacement of eggs with WPI solution in pound cakes(Table 3). Cakes with 50% of egg replacement had significantly lowerbaking loss (from ~31 to 33%) than the control (34.4%) (p b 0.05).Between them, the cakes prepared with the 20% (w/v) WPI solutionshowed significant differences (p b 0.05) when compared to cakesprepared with WPI solution of lower concentration (17 and 14% w/v),while no change was observed upon emulsifiers’ addition. As thepercentage of egg replacement increased from 50 to 100%, the bakinglosses decreased to 28.04%. The greater capacity of whey proteins forbinding water could explain the decrease in the loss of weight duringbaking observed in the case of WPI addition (de Wit, 1998). This couldalso be explained by the lower cell number of most of these cakes(Fig. 1) leading to the formation during the baking process of a smallernumber of channels and resulting in moderate water loss compared tothe rest.

3.3. Texture evaluation

The influence of egg replacement with the WPI solution on cakehardness, springiness, cohesiveness and chewiness is presented inTable 4. All egg-reduced cakes showed significantly higher hardnessparameter values than the control, while maximum hardness(10.20 kg) was noted for cakes containing only the 20% (w/v)WPI solu-tion (sample C). On the other hand, in the case of partial egg

A

B1 B1a

B2 B2a

B3 B3a

Fig. 1. Binarised images of scanned crumbs of the studied cakes.

76 A. Paraskevopoulou et al. / Food Research International 69 (2015) 72–79

replacement, as the concentration of the WPI solution decreased, thehardness values decreased as well (p b 0.05), while similar hardnessvalues (~4.4 kg) were recorded for the cakes prepared with the 17and 14% (w/v) protein solutions in the presence or not of emulsifiers(samples B2, B2a, B3 and B3a). These results are consistent with thecakes’ volume reported before (Table 3) and could be attributed to adenser crumb structure stemming from the observed decline in the bat-ter aeration and heat-induced protein coagulation. WPI addition

Table 4Texture parametersa of pound cakes 24 hours after baking.

Cake sample b Hardness (g) Springiness

A 3256±259 a 0.750±0.01B1 5937±439 c 0.770±0.02B1a 5761±337 c 0.751±0.01B2 4470±262 b 0.761±0.01B2a 4444±380 b 0.757±0.00B3 4426±469 b 0.752±0.01B3a 4273±424 b 0.760±0.01C 10200±489 d 0.742±0.00

a The values presented are the average obtained from three sets of 5 cakes. Different lettersb For sample codes see Table 1.

brought about an increase, the extent depending on protein content,in crumb hardness probably as a result of the crumb walls surroundingthe air cells and the strengthening of the crumb structure by the proteinparticles.These results agree with those obtained by Gómez, Oliete,Rosell, Pando, and Fernández (2008) who observed that addition ofchickpea flour in cakes also induced an increase in their initial firmness.Moreover, in their recent work Paraskevopoulou, Amvrosiadou,Biliaderis, and Kiosseoglou (2014), who studied the influence of eggyolk or yolk plasma addition on the rheological properties and flavourcharacteristics of heat-set gels based onWPI, suggested that a reinforce-ment ofWPI gel structuremay take place following incorporation of eggyolk constituents, indicating a possible synergistic effect between theconstituents of the two materials.

The texture profile analysis also revealed that the partially egg-replaced cakes, prepared with the 20% (w/v) WPI solution, exhibitedhigher springiness (0.770) and cohesiveness (0.518) compared withthe control (0.750 and 0.473, respectively) (p b 0.05). Nevertheless,the incorporation of HPMC and SSL gave cakes with values similarto those of the control, as the data of Table 4 clearly indicate. In gen-eral, both parameters are considered as a measure of the resistanceof the cake structure to compression, pointing out to the develop-ment of internal bonding in a three-dimensional protein network,an aspect fully associated with the consumer acceptance. Upon addi-tion of WPI solutions of lower concentrations, no significant differ-ences (p N 0.05) in cohesiveness and springiness of any of the cakeswere found, while a significant difference was observed in the cohe-siveness when eggs were totally substituted (Table 3). Additionally,the cakes prepared with the WPI solutions presented higherchewiness values than those prepared with the liquid egg, with thisdifference being more evident in the samples C containing only the20% (w/v) WPI solution (~3.5-fold). When the addition level aswell as the concentration of the WPI solution incorporated into thecakes decreased, the chewiness value decreased significantly, butwithout reaching the chewiness parameter values of the control(p b 0.05). The above results were confirmed by the analysis of thestress - strain curves obtained from the texture analyzer (Fig. 2). Asshown, the egg-reduced cakes prepared with the 17% and 14% (w/v) WPI solutions exhibited a behaviour similar to that of the controlcake, indicating that substitution of egg proteins with whey proteinsas well as the simultaneous incorporation of emulsifiers yielded acrumb as resistant to deformation as that of the control. Based onthe suggestion of Lillford and Judge (1989) that the final cake struc-ture is a solid foam characterized by extensive cell connectivity andcell walls of rather low elasticity, it could be postulated that incorpo-ration of whey proteins into cake brought about a modification ofcrumb structure development and resulted in the alteration of thefinal product’s mechanical properties. The positive effect of HPMCand SSL addition on cake textural parameters, observed in the caseof using WPI solutions of relatively low concentration, could beexplained by their ability to form interfacial films at the boundariesof the gas cells that confer some stability to the cells against the gasexpansion and processing condition changes (De Leyn, 2014).

Cohesiveness Chewiness (g)

6 a,b 0.473±0.012 a 1185±297 a0 d 0.518±0.009 b 2386±327d6 a,b 0.504±0.007 b 2204±246 c5 b,c,d 0.476±0.021 a 1628±292 b9 b,c 0.466±0.006 a 1539±115 b9 a,b 0.478±0.011 a 1594±63 b7 b,c,d 0.475±0.015 a 1534±95 b8 a 0.541±0.013 c 4055±208 e

in the same column are significantly different (p b 0.05).

0

5000

10000

15000

20000

25000

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Stre

ss (N

/m2 )

Strain (-)

AB1B1aB2B2aB3B3aC

Fig. 2. Stress–strain curves obtained by compression of control and egg-reduced cakes24 h after baking.

0

20

40

60

80

100

120

140

160

180

0-24h 0-48h 0-96h

Har

dnes

s inc

reas

e (%

)

AB1B1aB2B2aB3B3aC

ab

a ab

c cc

aa

a

bbb,c

b,c

c

d

d

bb

c,d

c

ee

Fig. 3. Increase (%) in hardness of control and egg-reduced cakes after storage at roomtemperature. Values are means of at least three replicates; mean values for the each stor-age period with a different small letter are significantly different (p b 0.05).

77A. Paraskevopoulou et al. / Food Research International 69 (2015) 72–79

3.4. Changes during storage

The preservation of cake freshness and sensory quality isassociated with the retardation of mechanisms being responsiblefor its deterioration during storage, i.e. crumb firming. This undesir-able phenomenon is mainly attributed to water migration and redis-tribution within cake crumb as well as to starch retrogradation (Gray& Bemiller, 2003; Wilderjans et al., 2013). In this work, the stalingpattern of the cakes was determined by measuring the change incrumb hardness, which is known to increase as a result of stalingsetting in. Fig. 3 shows the change in hardness of cakes (expressedas % hardness increase) over 4 days of storage under ambientconditions. Crumb hardness of all the cakes increased with storagetime, regardless of the treatment, while the extent of WPI incorpora-tion and the presence of emulsifiers produced different effects oncrumb hardness. As can be observed in Fig. 3, the hardness increasedwith the time of storage, but this increase was greater for controlsamples when compared to egg-reduced samples (p b 0.05). Morespecifically, the maximum hardness value increase (~167%) wasnoted for the control cake after 4 days in storage, while all thecakes prepared by 50% substitution of egg by WPI showed a lessextensive hardness increase (from 108 to 132% for the cakes B1, B2and B3) for the same storage period. In general, the addition of WPIdelayed cake firming, while the increase in hardness with ageingwas even lower when this was combined with HPMC and SSLaddition (p b 0.05). As Fig. 3 shows, WPI in admixture with HPMC andSSL proved effective for obtaining softer cakes as their incorporationdiminished the hardening of the egg-reduced cakes during storage.Prevention of crumb hardening was even more evident in the case ofthe B3a cake sample (prepared with the 14% WPI solution) whichexhibited the lowest change in hardness compared with the other twoemulsifier-containing samples. The positive effect of the emulsifierson the texture of cakes stored for 4 days could be explained by theirwater affinity as well as their interaction with starch that affects itsretrogradation, as was confirmed for bread by many authors (Armero& Collar, 1998; Collar, 2003; Gómez et al., 2004; Stauffer, 2000). HPMChas been reported to affect the retrogradation and thus delay breadstaling by either limiting both the diffusion and the loss of water frombread crumb and/or interacting with the starch constituents andmodifying starch structure (Bárcenas & Rosell, 2005; Davidou, LeMeste, Debever, & Bekaert, 1996; Rojas, Rosell, & Barber, 1999). Like-wise, emulsifiers, such as SSL, are widely used in commercial bread for-mulae to strengthen the dough or soften the crumb (Goesaert et al.,2005; Gray & Bemiller, 2003; Stampfli & Nersten, 1995). Their anti-staling effect is largely based on their hydrophilic–lipophilic index andpotential for ionization (Armero & Collar, 1998; Gray & Bemiller,2003; Stampfli & Nersten, 1995), which influences their interactions

with proteins and intact starch granules or their constituent polymers.According to Kurakake, Hagiwara, and Komaki (2004), the hydrophobicgroups of the emulsifier formwater-insoluble inclusion complexeswithamylose and linear chains of amylopectin, which during aging, unlikethe amorphous starch that crystallizes into B-type crystals, remain un-changed and decelerate crumb firming by “preventing migration ofstarch polymer molecules during baking and reducing the redistribu-tion of water from gluten to starch” as Gray and Bemiller (2003) report.

3.5. Cake microstructure

For gaining a further insight into the effect of the replacement ofwhole egg proteins by WPI on the cake microstructure, cryo-SEM anal-ysiswas applied. Fig. 4 depicts themicrographs of crumbof the cake for-mulations, i.e. A, B1, B1a, B2, B2a, B3 and B3a. As can be seen (Fig. 4a),the gas cell walls of the control cake are thin and show a smooth struc-turewith round cavities of various sizeswhich seem to be interconnect-ed. Upon the replacement of half of the liquid eggs byWPI solution (20,17 or 14% w/v) (Fig. 4b, d, f), the gas cell walls became thicker, the cakestructure remained smooth while gas cells appeared to be less in num-ber which is in agreement with previous findings reported above(Table 3). The addition of emulsifiers resulted in larger gas cells, irregu-lar in shape and either more (Fig. 4c) or less (Fig. 4e) in number, whilethe gas cell walls appeared to be thicker and the cake continued to showa smooth structure. Finally, when a WPI solution of a lower concentra-tion was used along with the emulsifiers, the gas cell walls remainedsmooth, thicker and uniform, but gas cells appeared larger, similar innumber to A and strongly interconnected (Fig. 4g). This synergistic ef-fect is in line with previous findings, since the emulsifiers allow the suc-cessful incorporation of WPI into the protein networks, and is probablythe cause that these cakes exhibited texture and crumb characteristicsvery close to the control ones (Table 4). Ashwini et al. (2009) reportedthat upon addition of combination of HPMC and SSL the protein matrixin eggless cakes appeared to be more uniform and continuous.

4. Conclusions

Partial or total whole liquid egg replacement by WPI solutions pro-duced pound cakes that exhibited lower volume and lower baking losscompared with the control, while the addition of emulsifiers into theWPI-incorporating products did not result in any significant improve-ment. Image analysis of the crumb revealed that WPI incorporation in-fluenced the crumb characteristics in a way that cells were less innumber and covered a smaller area, while in the presence of emulsifiersthe crumbs had a similar appearance compared with that of the control

a

b c

d e

A

B1 B1a

B2aB2

B3aB3f g

Fig. 4. Cryo-SEM images (magnification 240×) of cakes prepared with (a) fresh eggs, A; (b) eggs -WPI solution (20% w/v)mixture, B1; (c) eggs -WPI solution (20%w/v) mixture & emul-sifiers, B1a; (d) eggs -WPI solution (17% w/v) mixture, B2; (e) eggs -WPI solution (17% w/v) mixture & emulsifiers, B2a; (f) eggs -WPI solution (14% w/v) mixture, B3; (g) eggs -WPI so-lution (14% w/v) mixture & emulsifiers, B3a.

78 A. Paraskevopoulou et al. / Food Research International 69 (2015) 72–79

79A. Paraskevopoulou et al. / Food Research International 69 (2015) 72–79

cake only in the case of 50% egg replacement. Concerning texture attri-butes, egg-reduced cakes showed higher parameter values and a ten-dency to reach those of the control upon decreasing the WPI solutionconcentration. Crumb hardness of all the cakes increased with storagetime, regardless of the treatment, while the extent ofWPI incorporationand the presence of emulsifiers produced different effects on crumbhardness. Prevention of crumb hardening was more pronounced inthe case of the cake sample prepared with the lowest concentration ofWPI solution. Microstructure studies confirmed the positive effect ofthe co-addition of whey proteins and emulsifiers in egg-reduced cakes.

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