Baking Characteristics of Chiffon Cake as Influenced
by Microbial Transglutaminase
Feng Wang,1,2 Weining Huang,1,3 Patricia Rayas-Duarte,4 Hongzi Wang,5 and Qibo Zou5
ABSTRACT Cereal Chem. 90(5):463–468
Protein modification via covalent bonds by using microbial transgluta-minase (TGase) has generated many processing functionality improve-ments in specific food ingredients. In this study, TGase was added into different cake portions (foam and yolk batter) at levels of 0, 0.5, and 1.0% (w/w, total protein weight basis). The treatment of 0.5% TGase in the yolk batter portion significantly (P ≤0.05) increased its emulsion activity. The addition of 1.0% TGase in the yolk batter portion significantly increased both foam stability and emulsion activity of cake batter, whereas the addi-tion in the foam portion only increased the emulsion activity of cake batter significantly (P ≤0.05). As the addition of TGase, in foam or in the yolk batter portion, rose from 0 to 1.0%, the specific volume of chiffon cake increased. Cakes with 1.0% TGase in the foam portion had the maximum specific volume, 7.078 mL/g, and the softest texture. SDS-PAGE was used to analyze the modifications of TGase to the protein fractions from differ-ent cake portions. The effect of TGase on protein fractions from the yolk batter portion was more evident than that on protein fractions from the foam portion. However, there was no significant difference between the protein fractions of cake batters with the same level of TGase in the foam and yolk portions, which suggested that the main substrates of TGase were yolk protein and wheat protein, instead of egg white protein.
Cake is a high-consumption food worldwide. Its quality, as judged by volume and crumb texture, is related to the gas bubbles encapsulated in the batter during mechanical mixing, which ex-pand during baking (Mizukoshi et al 1980; Lee and Lin 2008). As a main ingredient for cake making, eggs not only enrich nutrition and offer attractive flavor (Pozo-Bayón et al 2007) but also pos-sess many positive functional properties such as foaming capacity, emulsifying activity, and gelling property, which might help main-tain the texture and structure of cakes during or after processing by incorporating and retaining air bubbles (Jones 2007; Kohrs et al 2010). Egg white is generally considered the protein-based foaming agent, and the function of egg yolk is involved in form-ing and stabilizing emulsions (Jones 2007).
The cross-linking enzyme transglutaminase (TGase, protein-glutamine γ-glutamyl transferase, EC 2.3.2.13) catalyzes an acyl-transfer reaction between the γ-carboxyamide group of peptide-bound glutamine residues and a variety of primary amines (Folk and Chung 1973). It was well documented that the modification of proteins could also bring about changes in protein functional properties. The treatment with TGase increased emulsion activity index of hydrolyzed wheat gluten at pH 6.5 (Agyare et al 2009). Soy protein modified by TGase showed improved emulsifying and foaming properties (Babiker 2000). Sakamoto et al (1994) reported that the breaking strength of egg white and egg yolk gels increased after being incubated with TGase. Because of its ver-satility as a protein modifier, TGase was considered a promis-ing enzyme for the food processing industry for meat, fish, and cereal-based food products among others (Motoki and Kumazawa 2000; Huang et al 2010; Wang et al 2011). Most recently, re-searchers also showed that the TGase mediated cross-linked pro-tein could 1) restabilize the damaged gluten network that was a consequence of freezing and frozen storage, and 2) provide im-proved rheological and breadmaking properties to the frozen dough (Huang et al 2008; Li et al 2011).
So far, only a few studies on the utilization of TGase in cake producing have been reported. Alp and Bilgi?li (2008) examined the influence of TGase on the properties of cakes enriched in vari-ous protein sources and found that the addition of TGase pro-duced good effects on volume and softness of cakes enriched in soy or milk proteins. The impact of TGase addition on the spe-cific volume and textural properties of sponge cake was studied by Yamazaki et al (2005). However, it was still unclear what the effects of TGase on the foaming and emulsifying properties of egg proteins were in a cake system and which proteins were the main TGase substrates in a cake system: egg albumin, egg yolk protein, or wheat gluten? To understand this question, further studies would be needed on the effects of TGase on the different portions of cake formulations, including egg white foam, egg yolk batter, and cake batter. Chiffon cakes were generally prepared by using a separated egg method (Lin and Lee 2005; Lee and Lin 2008). In the present study, TGase was added into different por-tions of chiffon cakes to evaluate the changes of functional prop-erties and protein profiles in different portions of chiffon cake formulations as a result of TGase treatments. The cake quality characteristics were also investigated.
MATERIALS AND METHODS
Materials
Fresh eggs and fine white sugar were purchased from a local market in Wuxi, China. Commercial wheat flour (unchlorinated) and soybean oil were purchased from Nanshun Flour Company (Shenzhen, China) and East Ocean Oils and Grains Industries (ADM joint venture, Zhangjiagang, China), respectively. The crude protein contents of egg white and egg yolk (N × 6.25, db), and of wheat flour (N × 5.7, db) were determined by the Kjeldahl method (AOAC method 984.13). Baking powder, cream of tartar, and microbial TGase (100 units/g) were obtained from Therm-phos (China) Food Additive Company (Xuzhou, China), Angel Yeast Company (Yichang, China), and Yiming Fine Chemicals Company (Taixing, China), respectively. Low-molecular-weight markers, including rabbit phosphorylase b (97,400), bovine serum albumin (66,200), rabbit actin (43,000), bovine carbonic anhy-
*The e-X tra logo stands for “electronic extra” and indicates that Figure 1 appears
in color online.
1 Research associate and professor, respectively, The State Key Laboratory of Food
Science and Technology, International Exchange and Cooperation Program,
School of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu,
214122, China.
2 Research scientist, MagiBake International, Inc., Wuxi, Jiangsu, 214131, China.
3 Corresponding author. Phone: +86 (510) 8591 9139. Fax: +86 (510) 8591 9139.
E-mail: wnhuang@https://www.doczj.com/doc/4a17746190.html,
4 Professor, Robert M. Kerr Food and Agricultural Products Center, Oklahoma
State University Stillwater, OK 74078-6055, U.S.A.
5 Research scientists, Fortune Bakery Co. Ltd., Zhangjiagang, Jiangsu 215632,
China.
https://www.doczj.com/doc/4a17746190.html,/10.1094/CCHEM-10-12-0140-R
? 2013 AACC International, Inc.
e-X tra*
Vol. 90, No. 5, 2013 463
drase (31,000), trypsin inhibitor (21,100), and hen egg-white lyso-zyme (14,400), were purchased from Sino-American Biotechnol-ogy Company (Shanghai, China). All reagents were of analytical grade.
Formulations of Chiffon Cake
The formulations of chiffon cake are listed in Table I. The addi-tion of TGase was based on the total weight of proteins (TPB), including egg white protein, egg yolk protein, and wheat protein, in cake formulations. In formulations 2 and 3, TGase was added into the egg white portion at levels of 0.5 and 1.0% (w/w, TPB), respectively, and in formulations 4 and 5, those same levels of TGase were added into the egg yolk portion. Formulation 1, con-taining no TGase, was used as the control.
Chiffon Cake Preparation
Cakes were prepared following the method of Lin and Lee (2005) with slight modifications. First, the egg white was sepa-rated from the egg yolk with an egg separator. For the yolk bat-ter preparation, egg yolk, fine white sugar, soybean oil, and wa-ter were poured into a mixing bowl and evenly mixed by hand with an egg beater (≈2 min). Then the sifted wheat flour and baking powder were added into the bowl. All ingredients were mixed until smooth (≈2 min). The egg white foam portion was prepared by mixing the egg white (≈25°C) and cream of tartar with a whisk attachment in a mixer (K5SS, KitchenAid, St. Jo-seph, MI, U.S.A.) at speed 4 to form big bubbles (≈20 sec). Fine white sugar was added to the egg white foam and mixed at speed 4 for about 5 min to form firm and slightly curved peaks when the whisk attachment was gently lifted from the mixing bowl. Then egg white foam was poured into the yolk batter and gently incorporated with a plastic scraper until smooth (≈1 min). The cake batter (mixture of egg yolk batter and foam portion, 35 g) was immediately poured into paper cake cups (6.5 × 7 cm, diameter × height) and tapped gently to level out the mixture before baking at 180°C for about 25 min in a preheated deck oven (SM-503, Sing Mine International, Wuxi, China). Cakes were taken out of the oven immediately after baking and turned upside down on a shelf for cooling (2 h, ≈25°C). After that, they were removed from the paper cups and packed in polypropylene bags for quality analyses. The baking experiments were per-formed in triplicate.
pH Measurement
The pH of the three main components (egg white foam portion, yolk batter portion, and cake batter) was measured with an MP225 pH meter (Mettler-Toledo, Switzerland). Samples (10 g) were homogenized with 90 g of sterile distilled water, and then the pH value was recorded. All tests were performed in duplicate. Liquid Drainage of Egg White Foam
It was difficult to characterize the volume of irregular egg white foam, so the liquid drainage of the egg white portion was measured to assess the foam stability affected by TGase treat-ment. The egg white portion was prepared as described earlier. Liquid drainage was calculated as the volume of liquid sepa-rated from 150 g of egg white foam in a 30 min period at room temperature (≈25°C), following the method reported by Abu-Ghoush et al (2010). Three replicates of each treatment were evaluated.
Emulsion Activity of Egg Yolk Batter
Egg yolk batter was prepared as described earlier. Emulsion ac-tivity was measured following a modified method of Shyu and Sung (2010). Egg yolk batter (30 g) was divided evenly into three 20 mL tubes and centrifuged at 2,000 × g for 20 min. The emul-sion activity was calculated according to the following equation: emulsion activity (%) = (height of emulsified layer/height of whole batter in the centrifuge tube) × 100. All tests were per-formed in triplicate.
Cake Batter Characteristics
The specific gravity of the cake batter (the mixture of egg white foam and egg yolk batter) was determined as the weight ratio of cake batter and water of the same volume. A portion of cake bat-ter (100 g) was transferred into a 1,000 mL graduated cylinder. The volume of foam held at room temperature (≈25°C) for 0 and 24 h was measured. The foam stability of cake batter was calcu-lated according to the following equation: foam stability (%) = (volume of cake batter held for 24 h/initial volume) × 100 (Shyu and Sung 2010). Emulsion activity of cake batter was measured with the same method described for the measurement of emulsion activity of egg yolk batter. The values presented represent the means of the three replicates.
Baked Cake Characteristics
The rapeseed displacement method (AACC International Ap-proved Method 10-05.01) was used to measure cake volume. Spe-cific volume of the cake was calculated as cake volume divided by cake weight.
Texture profile analysis of cake samples (3 × 3 × 3 cm) with crust removed was performed as described by Lin and Lee (2005) with a TA-XT2i texture analyzer (Stable Micro Systems, Godalm-ing, U.K.). The firmness and springiness of cakes were recorded. Three replicates of each treatment were evaluated.
Protein Extraction and SDS-PAGE
Protein was extracted from an aliquot of 0.5 g of each sample, egg white foam, egg yolk batter, and cake batter. One milliliter of SDS sample buffer (containing 3% Tris, 4% SDS, 4 mmol/L EDTA·2Na, and 10% 2-mercaptoethanol) was added (Tseng and Lai 2002), and the samples were heated in boiling water for 10 min, vortexed, and centrifuged at 8,000 × g for 5 min.
A 12% separating gel (pH 8.8) and 5% stacking gel (pH 6.8) were used (Huang et al 2010). The protein concentration of sam-ples was diluted with sample buffer until clear protein bands in gels were obtained, and sample volumes of 15 μL were loaded into each well. Electrophoresis was performed at 12 mA for the first 20 min and then increased to 20 mA for the remainder of the run, using an electrophoresis apparatus (DYY-8C, Beijing Liuyi Instrument Factory, Beijing, China). After completion of a run, gels were removed from the glass plates, stained overnight with 0.25% Coomassie brilliant blue, and then destained in 10% acetic acid (Huang et al 2010).
TABLE I
Formulations for Chiffon Cakes and
Microbial Transglutaminase (TGase) Treatments
Formulations (g)
Ingredients z 1 2 3 4 5 Egg
yolk
batter
Egg
yolk 100 100 100 100 100 Fine
white
sugar
36 36 36 36 36 Soybean
oil 48 48 48 48 48 Water 70 70 70 70 70 Wheat
flour 100 100 100 100 100 Baking
powder 3 3 3 3 3 TGase
(%) 0 0 0 0.5 1.0 Egg white foam
Egg
white 200 200 200 200 200 Fine
white
sugar
72 72 72 72 72 Cream
of
tartar 3 3 3 3 3 TGase (%) 0 0.5 1.0 0 0
z TGase was added into different portions of chiffon cake formulations (w/w) based on the total weight of proteins (including egg white, egg yolk, and wheat flour protein) in the formulations.
464 CEREAL CHEMISTRY
Statistical Analyses
One-way analysis of variance was performed with the SAS sta-tistical software package (SAS Institute, Cary, NC, U.S.A.). A significance level of 5% was adopted for all comparisons. Dun-can’s multiple-range test was used to determine the significant difference between different treatments.
RESULTS AND DISCUSSION
Protein Contents of Egg White, Egg Yolk, and Wheat Flour The protein contents of the egg components averaged 11.6 and 15.2% (mb) in egg white and yolk, respectively. The protein con-tent of wheat flour was 7.2% (mb).
Effect of TGase on the Functional Properties
of Egg White Foam and Yolk Batter
Egg white is a good foaming agent and plays an essential role in foam formation in cake making because of the dispersion and incorporation of a large volume of air into cake batter. Foaming properties of ovalbumin were affected by several factors including protein concentration, pH, intermolecular interactions, and so on (Kinsella and Phillips 1989; Hammershfj et al 1999), which might change the conformation of molecules, molecular flexibility, and thus stability of protein molecules at the interfaces. Egg white proteins had two ranges of pH at which good foaming properties were observed: pH 8–9 and 4–5, the latter being their isoelectric pH (Fennema 1996). In this study, the pH values of foam portions and yolk batter portions averaged 7.92 and 6.84, respectively, and they were not affected by TGase (data not shown).
As storage time increased, the volume of egg white foam de-creased, and the foam became watery. Liquid drainage of egg white foams generally correlated negatively with foam stability (Liang and Kristinsson 2007). In the current study, no significant difference (P ≤0.05) was found in the liquid drainage of the foam portion because of TGase treatment (Table II). During the meas-urement of emulsion activity of egg yolk batter, the centrifugation of the yolk batter resulted in four separated layers: an emulsified layer at the top or cream, an aqueous portion, a gummy layer, and the starch layer at the bottom of the tube. Similar results were reported by Guy and Sahi (2006). Compared with the control without TGase, the emulsion activity of the yolk batter portion increased significantly (P ≤0.05), from 0.207 to 0.221 after treat-ment with 0.5% (w/w, TPB) TGase, and no detectable separation of the emulsified layer from the liquid layer was observed in the yolk batter portion treated with 1.0% TGase (Table II). During the formation of the emulsion system, the modification of egg yolk protein by TGase might increase the stability of the interfacial film between oil and water in the emulsion system. Several fac-tors could contribute to the enhancement of emulsion activity, and they require more research. We speculated that the cross-linking of proteins catalyzed by TGase might slow down the separation of oil and water by changing the surface charge, hydrophobicity, and adsorbed protein film properties. The polymerizing of proteins reduced electrostatic repulsion by decreasing the number of amino groups, resulting in enhanced protein absorption on the oil–water interface and increased strength of the interfacial pro-tein film. Also, steric repulsion resulting from the TGase-induced high-molecular-weight polypeptides could prevent close contact of oil droplets and decrease flocculation and coalescence (Agyare et al 2009).
Effect of TGase on the Properties of Cake Batter
The addition of TGase into both foam and yolk portions of cake batter did not change the specific gravity significantly (at P ≤0.05) when compared with control cake batter containing no TGase (Table III). Cake batter with 0.5% (w/w, TPB) TGase in the egg white foam portion exhibited a slight increase in the spe-cific gravity, whereas the one with 1.0% TGase in the yolk batter portion was slightly reduced. Increased emulsion activity of the yolk batter portion by adding TGase might result in a lighter cake batter.
The foam stability of cake batter was increased by TGase treat-ment, either in the foam portion or in the yolk batter portion. Cake batter with 1.0% (w/w, TPB) TGase in the yolk batter por-tion had the maximum foam stability value and was significantly different than the control foam stability (Table III). The addition of TGase could also increase the emulsion activity of cake batter significantly, except for the one with 0.5% (w/w, TPB) TGase in the foam portion (Table III).
Baking Qualities of Chiffon Cake
After adding TGase in the foam portion, the specific volume of chiffon cake was significantly raised. Cake with 1.0% (w/w, TPB) TGase in the foam portion had the maximum specific volume, 7.078 mL/g, which was 20.2% higher than that of the cake with-out TGase (Table IV). The addition of TGase in the yolk batter portion also increased the specific volume of cake significantly (P ≤0.05) when compared with that of the control (5.888 mL/g). As the addition of TGase in the yolk portion increased from 0.5 to 1.0%, the specific volume of cake rose from 6.434 to 6.833 mL/g. This increase suggested that the addition of TGase, either in the foam portion or in the yolk batter portion, could increase the spe-cific volume of chiffon cake. Similar results were given by Yama-
TABLE II
Effects of Transglutaminase on Functional Properties of Foam Portions and Yolk Batter Portions of Chiffon Cakes z
Transglutaminase Level (%)
Foam Portion,
Liquid Drainage (mL)
Yolk Batter Portion,
Emulsion Activity
0 2.03
± 0.26a 0.207 ± 0.010b
0.5 1.98
± 0.24a 0.221 ± 0.010a
1.0 1.92
± 0.15a nd
z Each value was expressed as mean ± SD (n = 3). Means with different letters within a column were significantly different (P≤ 0.05). When emulsion activity of yolk batter treated with 1.0% (w/w, total protein weight basis) transglutaminase was determined, no separation of the emulsified layer from the liquid layer was observed; nd = not detected.
TABLE III
Properties of Cake Batters as Affected by Transglutaminase Treatment y
Cake Batter z Specific
Gravity
Foam
Stability (%)
Emulsion
Activity (%)
1 0.395
± 0.007ab 0.735 ± 0.021b 0.389 ± 0.005b
2 0.406
± 0.015a 0.752 ± 0.002ab 0.383 ± 0.028b
3 0.399
± 0.014ab 0.759 ± 0.005ab 0.508 ± 0.012a
4 0.391
± 0.008ab 0.762 ± 0.010ab 0.479 ± 0.018a
5 0.373
± 0.003b 0.778 ± 0.005a 0.507 ± 0.014a
y Each value was expressed as mean ± SD (n = 3). Means followed by different letters within a column were significantly different (P≤ 0.05).
z Cake batter preparation used the formulations listed in Table I.
TABLE IV
Effects of Transglutaminase Added in Different Portions of Cake Batter on the Specific Volume and Textural Properties of Chiffon Cakes y Cake z
Specific Volume
(mL/g)
Firmness
(g) Springiness
1 5.888
± 0.255d 81.226 ± 5.339a 0.860 ± 0.033a
2 6.079
± 0.100cd 78.853 ± 2.656a 0.844 ± 0.025a
3 7.078
± 0.398a 43.433 ± 4.809c 0.853 ± 0.034a
4 6.434
± 0.259bc 56.916 ± 7.899b 0.820 ± 0.032a
5 6.833
± 0.109ab 47.250 ± 1.750bc 0.816 ± 0.002a
y Each value was expressed as mean ± SD (n = 3). Means followed by different letters within a column were significantly different (P≤ 0.05).
z Cake preparation used the formulations listed in Table I.
Vol. 90, No. 5, 2013 465
466 CEREAL CHEMISTRY
zaki et al (2005), who reported increasing specific volume of sponge cake after TGase treatment. However, it should be noted that large pores or cavities were observed in cakes with 1.0% (w/w, TPB) TGase added in the yolk batter portion (Fig. 1, formu-lation 5), although not in cakes with 1.0% (w/w, TPB) TGase in the foam portion of the cake batter (Fig. 1, formulation 3). Large pores suggested localization of areas where increased coalescence of the air bubbles occurred before the gelatinization of starch dur-ing cake baking. Such areas might represent increased domains of protein secondary and tertiary structures that required a longer time from their initial adsorption to achieve maximal surface pressure (Graham and Phillips 1979; Shridas et al 2001).
Addition of 0.5% (w/w, TPB) TGase into the foam portion of cake batter had no significant effect on the firmness of chiffon cake when compared with that of the cake without TGase (Table IV). As the addition level of TGase increased to 1.0% (w/w, TPB), the firm-ness of chiffon cake was reduced by 46.5%. This reduction was partially related to the specific volume of the cake. The addition of 1.0% (w/w, TPB) TGase into the foam portion significantly in-creased the specific volume of chiffon cake, resulting in softer cake with more open and even pore structure. It was hypothesized that, when adding 0.5% TGase into the foam portion, most of the en-zyme was consumed in the reaction with egg white proteins. When 1.0% TGase was used, more of the enzyme remained after reaction with egg white proteins and further catalyzed the reaction with egg yolk protein or wheat gluten, which affected the cake firmness
significantly. Addition of TGase in the yolk batter portion also re-duced the firmness of cake significantly (P ≤ 0.05). Yamazaki et al (2005) reported that the addition of 7% (w/w, TPB) TGase (20 units/g) increased the softness of sponge cake.
Springiness of chiffon cake was not changed significantly (at P ≤ 0.05) by adding TGase, as shown in Table IV .
Effect of TGase on Protein Profiles of Chiffon Cake Components Analyzed by SDS-PAGE
SDS-PAGE analysis was used to record changes in protein pro-files of each cake component as a result of TGase treatment.
Egg white is a mixture of proteins, with each of its components performing a specific function to confer excellent foaming prop-erties (Cotterill and Winter 1955). From the electrophoretic bands in Figure 2, lane 2, the main protein components of egg white could be identified: ovalbumin (molecular weight, 46,000), lyso-zyme (14,300), and conalbumin (≈76,000) (Raikos et al 2006). After adding TGase to the foam portion, no significant changes were found in the protein fractions of egg white foam in the sepa-rating gel. Only a slightly stained band was observed at the top of separating gel in the sample of foam portion treated with 1.0% (w/w, TPB) TGase (marked as A, lane 4). This band might be evidence of the formation of higher-molecular-weight protein polymers through intermolecular cross-linking of the glutamine and lysine reactive residues in ovalbumin. The large molecular size of the polymers prevented them from entering the gel. A sim-
Fig. 1. Pictures of chiffon cakes with different portions of cake batter treated with transglutaminase: cake 1, 0%; cake 2, foam portion, 0.5%; cake 3, foam portion, 1.0%; cake 4, yolk portion, 0.5%; and cake 5, yolk portion, 1.0%.
Fig. 2. SDS-PAGE protein profiles of foam portions (lanes 2–4) and yolk batter portions (lanes 5–7) treated with transglutaminase (TGase) at the levels of 0, 0.5, and 1.0% (w/w, total protein weight basis), respectively, and of cake batters prepared with the formulations listed in Table I (lane 8, without TGase; lanes 9 and 10, 0.5 and 1.0% TGase in the foam portion, respectively; lanes 11 and 12, 0.5 and 1.0% TGase in the yolk batter portion,
respectively) . Lane 1 is a molecular weight standard.
ilar result has been presented on the reaction of TGase with egg albumin by Lim et al (1998), who also found that the preheating of egg white made the protein more susceptible to TGase.
The effect of TGase on the protein fractions of egg yolk batter was more evident compared with that on the protein fractions of egg white foam. Lane 5 shows the protein profile of egg yolk batter, which contained the proteins from both egg yolk and wheat flour. The intensities of protein bands at the top of the lanes in-creased (lanes 5–7, marked as B) after TGase treatment. A new light protein band (marked as C) was observed in the protein frac-tion of egg yolk batter with 1.0% (w/w, TPB) TGase (lane 7). Therefore, it could be concluded that new protein polymers were formed by the catalysis of TGase.
After adding TGase into different portions (the foam and yolk batter portions) of cake batter at different levels, the effects of TGase on the protein fractions were investigated. For cake batter with TGase in the foam portion, the intensity of protein bands at the top of separating gel slightly increased as the TGase addition rose from 0 to 1.0% (lanes 8–10, marked as D). A new separated protein band at molecular weight of ≈66,000 (lane 10, marked as E) was observed in the protein fraction of cake batter with TGase in the foam portion. It was formed mainly after blending yolk emulsion with egg white foam, and its intensity was enhanced as the addition of TGase increased from 0.5 to 1.0% (w/w, TPB). This finding might suggest that TGase could react better with yolk protein or wheat protein than with egg white protein. Wheat protein was reported as a better substrate of TGase than egg albu-min (Wang et al 2011). The reason that TGase affected egg white, egg yolk, and wheat proteins to different extents might be ex-plained by the variation of the molecular structure and the acces-sibility of glutamine and primary amines. TGase treatment had similar effects on the protein fractions of cake batters with TGase in the yolk batter (lanes 11 and 12) as those with TGase in the foam portion (lanes 9 and 10). There was no significant difference between the protein fractions of cake batters with the same level of TGase in the foam portion and yolk portion.
CONCLUSIONS
TGase treatment in the foam portion of chiffon cake did not change the foam stability significantly (at P ≤0.05), whereas addition in the yolk batter portion significantly (P ≤0.05) in-creased the emulsion activity. Cake batter with 1.0% TGase in the yolk batter portion slightly reduced its specific gravity value. The addition of 1.0% TGase in the yolk portion significantly increased both foam stability and emulsion activity of cake batter, whereas the TGase addition in the foam portion only increased the emul-sion activity of cake batter significantly (P ≤0.05).
As the addition level of TGase either in the foam portion or in the yolk batter portion rose from 0 to 1.0% (w/w, TPB), the spe-cific volume of chiffon cake increased. Cakes with 1.0% TGase in the foam portion had the maximum specific volume, 7.078 mL/g, and had the softest texture. TGase treatment in the yolk batter portion could also significantly (P ≤0.05) reduce the firmness of cake. No significant change on cake springiness was found after TGase addition. TGase addition in the foam portion resulted in the partial formation of large-molecular-weight protein polymers that did not enter the separating gel. The effect of TGase on pro-tein fractions from the yolk batter portion was more evident com-pared with that on the protein fractions from the foam portion. However, there was no significant difference between the protein fractions of cake batters with the same level of TGase in the foam portion and yolk portion, which might suggest that the main sub-strates of TGase were yolk protein and wheat protein, instead of egg white protein. Therefore, more studies are needed to deter-mine the specific proteins of each portion that were polymerized by TGase and sensory evaluation of the products to guide the addition of TGase in cake making processes according to those specific proteins. The positive functional roles of TGase, as a novel enzyme, in a cake system will make a good technical con-tribution to the cake baking industry.
ACKNOWLEDGMENTS
We are grateful for financial support from the National High Tech-nology Research and Development Program of China (863 Program, 2012AA022200), the National Natural Science Foundation of China (31071595 and 20576046), the National Agricultural Science and Tech-nology Achievement Transfer Fund Project of China (2011GB2C100017), the Joint Chan-Xue-Yan Project of Guangdong Province and the Ministry of Education of China (2011B090400592), Key Science and Technology R&D Program of Jiangsu Province, China (BE2011380), and MagiBake International, Inc. (Wuxi, China).
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[Received October 31, 2012. Accepted March 26, 2013.]
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