Quality evaluation of egg-free cake from soft tofu

Abstract

Soft tofu was used to produce a cake to ascertain its suitability in producing egg-free cake (EFC) for vegans and individuals allergic to eggs. A conventional cake (CVC) served as control and the quality characteristics of the EFC and CVC were evaluated. Results showed the egg-free cake had physical properties which were significantly (p < 0.05) higher in weight (1611 g), density (0.81 kg/m³) and specific volume (1.23%) than Conventional cake (1516 g, 0.61 kg/m³ and 0.25%, respectively). CVC showed significantly p < 0.05 higher height (8.50 cm) and volume (2644.78 m³) which is desirable in the baked cake. EFC showed significantly p < 0.05 higher values in ash (3.13%), moisture (24.01%), fibre (2.40%) and carbohydrate (52.34%), while CVC had significant (p < 0.05) higher values in protein (7.38%) and fat (16.34%). The taste (0.55), colour (0.55), texture (0.55) and aroma (0.55) of EFC was more preferred than CVC (0.45, 0.40, 0.45 and 0.45, respectively). Soft tofu showed suitability and an acceptable replacement for egg in making Egg-free cakes for vegetarians and individuals allergic to egg.

Introduction

Cakes are one of the most typical bakery goods, which are semi-dry foam foods with air pockets contained in a protein and carbohydrate network (Shi et al. 2011). Cakes are classified into several types based on ingredients and mixing techniques which are: butter, plain, chiffon, chocolate, egg-free cake, sponge cake, among others. An egg-free cake is a cake baked with egg substitutes and is usually consumed by people with specific dietary needs such as vegetarians, vegans and people with egg allergy (Castella 2010). Because of egg’s ability to increase the number of air cells and thus contribute to the desired leavening of the product, eggs are an essential ingredient in the traditional cake-making process. For vegans, vegetarians, and cake lovers with egg allergies, the presence of egg is a deterrent to cake consumption. As a result, these groups are actively looking for healthier food options that don’t sacrifice taste or aesthetic, so therefore, food makers are continuously looking for egg substitutes in cake recipes. Egg has been replaced with mashed banana (Braveman 2019), applesauce (Honeycutt 2019), ground flaxseed (Christensen 2019) or chia seeds (Anwar et al. 2020) among others in the quest of producing egg-free cakes (MacDonell 2017). When creating a traditional cake, eggs increase the number of air cells in the batter, which helps the cake rise. Using soft tofu, a product of soybean could be a perfect substitute for egg in making egg-free cake because the texture of soft tofu is easy to trap air cells and be incorporated during the mixing of cake batter and it also shares a comparable protein content (10.02%) with egg (12.60%).

Soybean is a leguminous crop that can be processed into different soy products like soymilk, soy powder, and tofu among others. Soy milk is coagulated to make tofu which is also known as soy curd. Tofu is made with coagulants such as citric acid, CaCl₂, or MgCl₂ (Nigari) or CaSO₄ and Glucono-d-lactone (GDL) (Murugkar 2015). Tofu is characterized by texture or consistency of its water content, the more water, the softer the tofu while with less water the tofu is firmer. It is characterized as soft (87–90% water content), regular (82–86% water content), firm (76–81% water content) and dry (< 76% water content) (Cai and Chang 1997). Soft tofu is the softest type of tofu and as such it adds a creamy texture when used as an egg substitute in cheese cakes, ice cream, sour cream or puddings (Tofupedia 2015). So many authors have tried replacing egg to produce egg-free products: Rahmati and Tehrani (2015) have worked on effect of soy milk on quality and sensory characteristics of egg-free cake; production of gluten-free cookies from germinated brown rice flour. have been carried out by Bolarinwa et al. (2019); Development of gluten-free and egg-free pasta based on quinoa (Chenopdium quinoa Willd) with addition of lupine flour, vegetable proteins and the oxidizing enzyme Pox, have been carried out by Linares-García et al. (2019); Teff, buckwheat, quinoa and amaranth were used to produce gluten-free egg-free pasta (Kahlon and Chiu 2015) among others.

The objective of this work was to produce conventional and egg-free cakes and determine the effects of soft tofu on quality of the egg free cakes in comparison to conventional cake, by evaluating physical properties (height, weight, volume, specific volume and density) of the cakes, chemical composition and evaluating sensory characteristics of the cake samples.

Materials and methods

Procurement of ingredients

Wheat flour (Golden Penny), margarine (Simas), granulated sugar (Dangote), baking powder (King Crown), eggs, baking pans and calcium sulphate (Qualikems India), magnesium sulphate (May and Baker, England) and soy bean were procured from Ogige market in Nsukka, Enugu state Nigeria. Potable water was gotten from the Department of Food Science and Technology’s tap.

Processing of soy bean into tofu

Soy bean was processed into tofu using a modified method of Yang and James (2013) as shown in flow chart (Fig. 1). A 500 g of soy bean was cleaned, sorted and soaked in 1000 ml of water for 24 h in a covered bucket. The soaked soy bean was drained, dehulled, washed and milled with 2000 ml of potable water. The milled soy bean was poured into a pot and cooked for ten minutes after it started boiling at 100 °C. It was poured into a cheese cloth and allowed to cool for easy handling. Soy milk was pressed out into a sterile container and 1000 ml of soymilk was measured out and poured into another heating pot. Coagulant quantity of 0.24% (0.024 g) of calcium sulphate and magnesium sulphate were weighed and dissolved in 15 ml of warm water and mixed vigorously to dissolve. The dissolved coagulants were divided into two portions respectively, the first portion was added to the soymilk heated to 80 °C, stirred, covered and allowed to boil at (100 ± 2 °C) for five minutes. The second portion was sprinkled on the surface of the soymilk, stirred for five seconds and covered again to boil for three minutes. Soy curd forms and the pot was removed from heat source. Figure 1 represents the flow chart for soy bean processing into tofu.

Fig. 1.

Processing of soy bean into tofu.

Source: modified method of Yang and James (2013)

Preliminary analysis

Proximate analysis according to AOAC (2010) of some selected raw materials (Table 1) were conducted to know the contribution of each to the final product.

Table 1.

Proximate composition of selected raw materials used in production of the cake samples (%)

Sample	Protein	Ash	Fat	Moisture	Fibre	Carbohydrate
Wheat flour	11.55 ± 0.1b	0.99 ± 0.09b	1.65 ± 0.05b	11.67 ± 0.1a	1.30 ± 0.05b	72.84 ± 0.05c
Tofu	10.02 ± 0.05a	2.49 ± 0.05c	1.45 ± 0.05c	87.99 ± 0.05c	2.69 ± 0.05c	5.36 ± 0.05b
Whole egg	12.60 ± 0.12c	0.80 ± 0.05a	9.0 ± 0.1a	76.78 ± 0.06b	0.00a	0.80 ± 0.05a

Values represent means score ± Standard Deviation of triplicate readings. Mean values with the same superscript within the same column are not significantly different (p > 0.05)

Proximate analysis

Proximate composition of the selected raw materials were measured using official methods of AOAC (2010). To determine the moisture content and crude ash of the samples a warm air oven at 105 and 600 °C, respectively was used. Fat content was determined using Soxhlet extraction apparatus. To measure the crude protein, the nitrogen content was determined by Kjeldahl’s method was converted. Carbohydrate was calculated by getting the sum of other proximate parameters including crude protein, crude fat, crude fibre, ash and moisture content, and deducting it from 100 as nitrogen free extract (NFE) as follows:

$$\%\text{carbohydrate}\left(\text{NFE}\right)=100\%-(\text{protein}+\text{fat}+\text{fibre}+\text{ash}+\text{moisture}).$$

Preparation of cake batters and the cakes

The batter was prepared by adopting a modified method of Connelly (2010) with a recipe as shown in Table 2. Wheat flour (500 g) and baking powder (15 g) were sieved together in a bowl. In a separate mixing bowl, margarine (500 g) and sugar (250 g) were creamed using a mixer until light and fluffy. Tofu (400 g) was introduced into the mixing bowl in small quantities, until all had been added. A Mixture of flour and baking powder were sequentially added to ensure a homogenous mixture. The batter obtained was poured in a greased baking pan (12 inches) and baked at 150 °C for 1 h 30 min using Julianti (2016) approach. When properly baked with indication of skewer inserted in the middle of the cake coming out dry and no batter sticking to the skewer, the cake was removed from oven, allowed to cool, wrapped using cling film and aluminum foil and labeled. The conventional cake was also prepared following the same procedure but egg (500 g) was used to replace tofu.

Table 2.

Recipe formulation for Conventional and Egg-free cake

Ingredients	Conventional egg (g)	Egg-free cake (g)
Flour	500	500
Egg	500	–
Tofu	–	400
Sugar	250	250
Baking powder	15	15
Margarine	500	500

Source: Modified recipe of Connelly (2010)

Physical analysis

The physical analysis of the cake which include the cake weight, volume, specific volume, density and height, were assessed using Ho et al. (2013) approach.

Cake weight

Cake weight was ascertained using a laboratory weighing scale calibrated in grams.

Volume of cake

The volume of cake was calculated using the expression (Eq. 1) according to Ho et al. (2013).

$$cakevolume\left({\text{cm}}^3\right)=\pi r^{2}h$$ 1

where: r = radius of the cakes, h = height of the cakes, π = pi.

Specific volume of cake

The expression (Eq. 2), was used to calculate the specific volume according to Ho et al. (2013).

$$Specificvolume\left({\text{cm}}^3/\text{g}\right)=\frac{cakevolume}{cakeweight}$$ 2

Cake density

The expression (Eq. 3) was used to calculate the density of the cakes according to Ho et al. (2013).

$$Density\left(\text{g}/{\text{cm}}^3\right)=\frac{cakeweight}{cakevolume}$$ 3

Height of cake

Using the centimeter rule, the cake height was computed as the average of three height measurements: the middle point height and two extreme highest points.

Proximate analysis of cake samples

The AOAC (2010) technique was used to determine the proximate composition of the cake samples Difference from all the other variables was used to calculate carbohydrate content.

$$\%\text{carbohydrate}=100-\left(\%\text{moisture}+\text{crude protein}+\text{crude fibre}+\text{ash}+\text{fat}\right)$$

Sensory evaluation of the cakes

Sensory evaluation of the cakes (egg-free and conventional cake) were evaluated. Twenty untrained panelist from The Department of Food Science and Technology, University of Nigeria, Nsukka were used. The panelists were chosen based on habitual cake eaters who were not sick or allergic to any foods. The sensory qualities of color, taste, texture, aroma, and general acceptability were evaluated using a paired comparison score card by panelists who had been trained in the use of the sensory evaluation methodologies. To avoid flavor transfer during the tasting, panelists were instructed to rinse their mouths with water after each rating.

Experimental design

The experimental design was completely randomized. Using SPSS (Statistical Package for Service solution) software version 22.0, the data were subjected to an independent paired comparison test (T-test). Duncan’s New Multiple Range Test (DNMRT) was used to compare the means and separate the standard deviations according to Steel and Torrie (1980) significance was accepted at p < 0.05.

Results and discussions

Physical properties

Plate 1, 2 and 3 shows the tofu sample, Conventional cake and egg-free cake images, respectively.

Table 3 shows the measurements of cake height, weight, density, volume and specific volume for the two samples EFC and CVC. The mean height for EFC and CVC were 6.0 and 8.5 cm, respectively. Sample CVC had a significantly (p < 0.05) higher value in height (8.5 cm). In reference to Sahi and Alava (2003), who reported on Functionality of emulsifier in sponge cake production, the significant (p < 0.05) differences in height for samples EFC and CVC could be due to the viscosity of EFC’s batter, which limited expansion during baking. Proteins are important in the production and stabilization of bubbles. The ability to be rapidly adsorbed at the air–water interface during bubbling, as well as undergo rapid conformational change and rearrangement at the interface, are the most basic characteristics for a protein to be a good foaming agent (Deak and Johnson 2007). A High amount and quality of proteins results in high foaming ability. Egg has a higher quality and protein content (12.60%) when compared with tofu (10.02%) therefore, sample CVC (conventional cake) having a higher quality and protein content and more gases in its air cells resulted in expanding the stretchy gluten in the flour more than is obtained in sample EFC (egg-free cake).

Table 3.

Physical evaluation of the cake samples baked using tofu and egg respectively

Sample	Height (g)	Weight (g)	Density (kg/m3)	Volume (m3)	Specific volume (%)
EFC	6.50b ± 0.05	1611a ± 0.05	0.81a ± 0.11	1866.90b ± 0.1	1.23a ± 0.05
CVC	8.50a ± 0.05	1516b ± 0.1	0.61b ± 0.05	2644.78a ± 0.1	0.25b ± 0.1

Values represent means score ± Standard Deviation of triplicate readings. Mean values with the same superscript within the same column are not significantly different (p > 0.05)

EFC Egg-free cake, CVC Conventional cake

The weight of sample EFC was 1611 g, which was significantly (p < 0.05) higher than the weight of sample CVC, which was 1516 g. This is probably because of the higher moisture content of tofu in egg-free cake than egg in CVC contributing its weight. According to Connelly (2010) proteins have the basic function of lowering interfacial tension, increasing the viscosity and elasticity of the liquid phase, and forming strong films. Expansion, setting, and browning are the three phases of baking. The gases in the air cells expand the stretchy gluten from the flour as the batter temperature rises, while the chemical leavening agents release carbon dioxide. When the batter hits 60 °C, water vapor forms, expanding the air cells even more. Around 90% of the subsequent expansion of the batter is attributable to carbon dioxide and water vapour, with the remaining 10% due to thermal expansion. As the egg and soy (tofu) proteins coagulate, the starch granules absorb water, swell, and form a gel, and the gluten loses its flexibility, the raised batter takes on its permanent shape at around 80 °C. The texture created at this moment is maintained until the cake is set by the coagulation of the egg, soy, and flour proteins found in the various cakes, resulting in the characteristic porous crumb structure. Batter with higher moisture content will be heavier as the starch granules absorb more water.

For the cake density, the mixing action added air into the batter, resulting in the production of little bubbles, which affected the cake density. The emulsifiers in both cake samples fulfill their role by trapping these bubbles (Rahmati et al. 2014; Ronda et al. 2011). During baking, the little air bubbles act as an early core to develop porosity. The density of cakes recorded for EFC and CVC was 0.81 and 0.61 kg/m³ respectively. The density of both cake samples had significant differences (p < 0.05). The density of the batter is an important physical feature to consider when determining the final density of a baked cake. The amount of air bubbles introduced into the batter is determined by the surface tension and viscosity of the cake batter, as well as the mixer design and speed. The lower the batter density, the more air bubbles will be integrated into the cake batter (Hedayati and Tehrani 2018). Egg yolk proteins reduce surface and interfacial tensions during batter mixing, resulting in the production of a stable emulsion (Wilderjans 2013). As a result, the sample CVC held more air bubbles and had a lower density. This result confirmed what was reported by Rahmati and Tehrani (2015), the cake density increased with increase in egg replacement having the highest density at 0.558 g/cm³ for the cake prepared with full replacement.

The cake volume for sample EFC was recorded as 1866.90 cm³ while that of sample CVC was 2644.78 cm³. Both samples had a significant difference in volume (p < 0.05). In general, a decrease in batter density was linked to an increase in cake volume. This is because, when cake batter is heated, the trapped air bubbles expand, resulting in an increase in cake volume (Sahi and Alava 2003). However, mixtures with a high density lack adequate air bubbles, limiting cake rise during baking. (Majzoobi et al. 2014). This can be due to the eggless cake’s (sample EFC) batter being excessively viscous before baking, resulting in an undesired relative decrease in volume. The final volume of the cake is not entirely determined by the batter density. The distinctive foaming, emulsifying, and heat coagulation capabilities of egg proteins, as well as water vaporization, could explain an increase in the volume of sample CVC (conventional cake). The decrease in volume of egg-free cake is consistent with a report by Rahmati et al. (2015), who found that increasing the percentage of soy milk in the cake formulation decreased the volume of egg-free cake. In addition, when comparing the gluten and whey protein isolate cakes to the control cake made with whole egg, Kohrs et al. (2010) found that the gluten and whey protein isolate cakes had smaller volumes.

The specific volume of the cake samples was significantly different (p < 0.05). The specific volume recorded for sample EFC (egg-free cake) was 1.23% while sample CVC (conventional cake) recorded 0.25%. The difference in the specific volume of both products is probably attributed to high density of cake batter obtained for sample EFC and a less density value for sample CVC.

Proximate composition

Table 4 shows the proximate composition for egg-free cake and conventional cake. Protein content of samples CVC and EFC were significantly (p < 0.05) different with values of 7.38 and 6.09% respectively. This is because the raw egg had a higher protein value of 12.60% compared to soft tofu (10.02%). The higher ash content of tofu (raw material) also reflected on the egg-free cake which recorded a substantial significant (p < 0.05) higher value of ash (3.13%) and when compared to the value of (2.25%) reported for conventional cake. Analysis of the raw material (tofu and egg) showed that tofu contained more ash (2.49%) than raw egg (0.80%). The egg-free cake and conventional cake recorded fat content of 13.50 and 16.34% respectively. This is as a result of higher fat content which was observed in egg (9.0%) as compared to tofu 1.45%. The crude fibre content of the cake products were 2.40 and 2.19% for samples EFC and CVC, respectively. The high fibre content is attributed to the incorporation of tofu which is a plant-based protein. Egg has a no fibre content when compared to tofu.

Table 4.

Proximate composition of the egg-free cake and conventional cake (%)

Sample	Protein	Ash	Fat	Moisture	Fibre	Carbohydrate
EFC	6.09b ± 0.1	3.13a ± 0.05	14.34a ± 0.05	21.70b ± 0.1	2.40a ± 0.05	52.34a ± 0.1
CVC	7.38a ± 0.05	2.25b ± 0.03	13.50b ± 0.05	24.01a ± 0.05	2.19b ± 0.1	50.67b ± 0.05

Values represent means score ± Standard Deviation of triplicate readings. Mean values with the same superscript within the same column are not significantly different (p > 0.05)

EFC Egg-free cake, CVC Conventional cake

Samples EFC and CVC had a moisture content of 24.01 and 21.70% respectively. In both samples, there was a significant (p < 0.05) difference. The changes in cake moisture content are most likely attributable to high moisture absorption capacity by processed protein-rich legume (tofu) and also tofu contained more moisture (87.99%) than egg. Sample EFC baked longer than sample CVC which is another indicator of the higher moisture content of tofu. Sample EFC had a substantially greater carbohydrate content (p < 0.05) than sample CVC, with values of 52.34 percent and 50.67 percent, respectively. The differences in carbohydrates can be attributed to higher carbohydrate content of the raw material tofu. Tofu recorded a carbohydrate content of 5.36% compared to 0.80% for raw egg.

Sensory results

The results for sensory analysis for cake samples EFC and CVC are shown in Table 5. Sample EFC’s colour (0.55) was preferred to sample CVC (0.45) although no statistically significant (p > 0.05) difference exist between them. The bright color of sample CVC was due to fat-soluble carotenoids in the egg, namely xanthophyll and moderate levels of carotenes, which were responsible for the cake’s vivid yellow-orange color and matched Ratnayake’s et al. (2012) findings. The aroma of Sample EFC (0.55) was preferred above Sample CVC (0.45), which could be due to the tofu utilized, which provided a novelty aroma that was more pronounced than that of sample CVC, despite the fact that there was no statistically significant (p > 0.05) difference between the two samples. Although there was no significant (p > 0.05) difference between EFC and CVC, sample EFC (0.55) had a better taste than sample CVC (0.45). Taste consistently outranks all other product criteria, according to an annual poll performed by the International Food Information Council Foundation. Consumers who purchase meals and beverages are influenced by taste or flavor. Despite the fact that eggs contain over 100 volatile flavor components, the overall effect is weak or bland (Vaclavik and Christian 2007).

Table 5.

Sensory scores of the baked cake samples

Sample	Colour	Aroma	Texture	Taste	Aftertaste	Mouthfeel	Overall acceptability
EFC	0.55a ± 0.05	0.55a ± 0.1	0.55a ± 0.05	0.55a ± 0.1	0.50a ± 0.05	0.50a ± 0.1	0.50a ± 0.11
CVC	0.40a ± 0.05	0.45a ± 0.05	0.45a ± 0.11	0.45a ± 0.1	0.50a ± 0.01	0.50a ± 0.05	0.50a ± 0.11

Values represent means score ± Standard Deviation of triplicate readings. Mean values with the same superscript within the same column are not significantly different (p > 0.05)

EFC Egg-free cake, CVC Conventional cake

Although there was no significant (p > 0.05) difference between the cake samples, sample EFC had a better texture than sample CVC. This is mainly because: soy lecithin caused more air bubbles to be incorporated into the batter, resulting in a softer texture in the cakes. The steam released during baking aids in the formation of additional air cells and the baking of porous, low-density cakes (Rahmati and Tehrani 2015). As revealed by Rahmati and Tehrani (2015), a higher ability of soy milk water absorption limits the amount of water available to produce steam, resulting in fewer air cells being produced in the cake crumb. This could probably be the reason for a lower, less porous texture in sample EFC. The after taste, mouthfeel and overall acceptability of sample EFC (0.50) was the same with sample CVC (0.50).

Conclusion

Acceptable nutritious egg‐free cake can be prepared using soft tofu for vegetarians. Vegans and individuals allergic to egg. Physical evaluation of the egg-free cake showed a high significant difference in density, weight and specific volume than in conventional cake while values for conventional cake in height and volume, was significantly higher than egg-free cake. Values for egg-free cake was significantly higher in ash, fat, fibre, moisture and carbohydrate (with exception of protein) than conventional cake. Taste or flavor is the determining factor for customers purchasing meals and beverages, outranking any other product sensory trait. A food product with high nutritional quality but poor sensory qualities may be minimally patronized by consumers, Likewise, a food product with poor nutritional quality but good sensory qualities will be acceptable and patronized by consumers. EFC having a higher sensory acceptability level in taste, colour and aroma, compared to CVC makes Soft tofu acceptable and suitable in making egg-free cakes for vegetarians, vegans and persons allergic to egg despite CVC having a higher protein content compared to that of EFC.

Author’s contribution

This research was carried out under the supervision of Nwosu, Adaora who originated the idea. The research was carried out as a B.Sc. project by Onyia-Akaa, Ugochi Christabel. The paper was edited and co-written by Azuka, Chinenye.

Funding

The research was carried out with personal funds.

Declarations

Conflict of interest

There is no conflict of interest.

Consent for publication

All authors have given consent for this work to be published I in JFST.