Development and Quality of Tofu Analogue Prepared from Whole

Chapter 18

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Development and Quality of Tofu Analogue Prepared from Whole Soybeans Fuh-Juin Kao,1 Nan-Wei Su,2 and Min-Hsiung Lee*,2 1Hospitality

Management Department, School of Tourism, Ming Chuan University, Taoyuan, Taiwan 2Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan *[email protected]

Okara is the insoluble residue after filtration of soymilk. In common, every pound of dry beans makes into soymilk or tofu generates about 1.1 pounds of okara with around 80% moisture. It contains high content of fiber and appreciable amounts of oil and protein with high quality. However, okara is generally used as feed or fertilizer. With the growing awareness of the importance of dietary fiber in human health, there is an increasing interest in the utilization of whole beans as an alternative. In this study, a whole-soybean tofu was developed. Whole-soybean tofu treated with fine milling and with particle size smaller than 425 µm could be successfully made just by means of calcium sulfate addition. It was found the tofu made with water-to-bean ratio at 12:1 gave maximal protein and solid recoveries, as well as the maximal tofu yield. However, the whole-soybean tofu possessed softer, less chewy texture, and coarse appearance. Nevertheless, whole-soybean tofu was rich in fiber and low in fat. It could be considered as a healthy food.

Introduction The soybean is one of the most valuable agricultural commodities because of its unique chemical composition. On the average, moisture content of stored mature soybeans is usually about 10-13%. On a dry basis, soybeans contain about 5-10% ash, 10% crude fiber, 16-22% crude fat, 40-50% crude protein, and about © 2010 American Chemical Society In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.


20% carbohydrate (1). Besides, soybeans also contain various macronutrients such as isoflavones, its contents range from 1000-4000 ppm dependent on soybean variety (2). In the eastern Asia, soybeans had been transformed into forms of soyfoods, such as soymilk, tofu, soy sauce, and tempeh. However, tofu has been the most popular way to serve soybeans as a food. Many different types of tofu have appeared in the market. Based on the water content and textural properties, tofu is generally classified into Momen, Kinu, and packed tofu (3). Basically, these tofus are made in a similar fashion except for variations in the water-to-bean ratio, the type of coagulants used, and the amount of whey being pressed out. In Taiwan, momen tofu is subclassified into three basic types, namely regular, firm, and dry tofu according to its water content. In general, for regular tofu, the moisture content should be about 87-89%; for firm tofu, 76-87%; and for dry tofu, less than 76% (4, 5). During tofu preparation, the soaked beans are ground with fresh water and then the slurry is filtrated. The residue, known as soy pulp or okara is separated from the filtrate. Therefore, okara is considered a byproduct during soymilk or tofu preparation, most of it is dumped and burnt as waste. However, to avoid environmental consequences of its disposal, developing a reusing technique for okara is highly encouraged. In fact, dry okara generally contains protein up to 18.232.2% protein, 6.9-22.2% oil, 9.1-18.6% crude fiber (6). Not only is okara a rich source of dietary fiber, it also contains a high quality of protein. The okara protein is generally of higher quality than that obtained from other soy products both in terms of the protein efficiency ratio and the essential amino acid to total amino acid ratio (7). Notably, secondary metabolites such as isoflavones outstandingly serve as a healthy dietary supplement. According to the report of Jackson et al. (8), the estimated total mass of isoflavones lost in okara was 28% during tofu preparation. This compound is known to help preventing osteoporosis, breast and ovarian cancer, and cardiovascular diseases (9, 10). Several studies have investigated the use of the okara, including preparing protein isolate from okara by isoelectric precipitation (11), extracting emulsionizing polysaccharides from okara by hydrolysis (12) using okara as a base for growing Bacillus subtilis to produce iturin A-a fungicide effective against serious plant pathogens (13). .In terms of food application, there are various ways of using okara. In some parts of China, okara could be fermented with various microorganisms for the production of meitauza which is a natto-like or tempeh-like product (7, 14). Basically, okara could be made into various types of food, including salad, sauces, bread (15), biscuit (16), and candy (17). However okara putrefies very quickly because its high moisture content, to overcome this problem, Chundubu which is a kind of Korean whole-tofu made from microparticulated soybean powder, and no okara generated during Chundubu preparation (18). Although it offered the benefit of not creating the environmental problem, it was not popular with consumer for its rough texture. Afterward Ku et al. (19) try to use merceating enzymes to reduce the particle size of the whole soybean powder, however the effect on the reduction of particle size of okara was not significant. Therefore, the okara-containing-tofu could be developed to some tofu analogue, which is no need of smooth mouthfeel and appearance, such as Aburage or Kori-tofu. Aburage is produced by frying fresh tofu in oil, while Kori278 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.


tofu is fresh tofu dehydrated through repeated freeze-thaw cycle, then turn into a sponge-like structure in the end. There are few reports about the method to make utilization of okara in tofu or its analogue, because the use of okara has been difficult, for the sake of high fiber content and unsavory texture for eating. In this preliminary study, we tried to develop a process for making whole-soybean tofu with texture properties similar to the common tofu or its analogue and without okara generated during manufacturing process. The effects of preparation conditions such as okara powder size, water-to-bean ratio, and transglutaminase treatment on quality and textural properties of whole-soybean tofu were investigated.

Materials and Methods Materials Soybeans of the Ohio FG1 cultivar were obtained from a local agency. Food grade calcium sulfate dihydrate (Ako Kasei Co., Ltd. Hyogo, Japan) was used as the coagulant in the tofu production and was obtained from Gemfont Corporation (Taipei, Taiwan). Food grade antifoaming agent (containing 90% glycerin fatty acid ester, 5% calcium carbonate, 4.3% soybean phospholipids, and 0.7% silicone resin) was obtained from Riken Vitamin Co., Ltd. (Tokyo Japan). Microbial transglutaminase (MTGase) preparation (0.044 U/mg) was a gift from Ajinomoto Co., Inc. The commercial MTGase preparation consisted of 0.2% MTGase, 60% sodium caseinate, and 39.8% maltodextrin. Conventional Tofu Making The procedure used for traditional tofu making was similar to that published by Cai and Chang (20) with some modifications. Aliquots of 300 g soybeans were soaked in tap water at 4°C for 9 h to bring the soaked beans weigh to approximately 2.2 times their initial weight.. After draining the initial soaking water, tap water was added to the hydrated beans to a final weight of 3300 g to give the water-to-bean ratios of 10:1. The mixtures were then ground with a soymilk grinder (Pineapple grinder, Great Yen Electric Food Grinder Co., Ltd. Taipei, Taiwan) equipped with an automatic centrifugal filter to separate raw soymilk from the residue. After grinding, the slurry was further filtrated through a 100-mesh sieve to remove the remaining okara. After adding 1 g of the antifoaming agent, soymilk was heated to boiling with gentle stirring and kept at boiling temperature (approximately 96 °C) for 5 min. After cooling to 73°C, 50 mL of calcium sulfate solution was added to the mixture to give the final CaSO4·2H2O concentration used in this mixture was 0.4% (w/v). Immediately after the addition of coagulant solution, soymilk milk was stirred at a speed of 250 rpm for 10 sec and then incubated for 20 min to form bean curd. The soybean curd was then broken slightly and transferred into a muslin cloth- lined stainless steel mold (13 x 13 x 5.5 cm3) and then pressed at 21.8 g/cm2 for 10 min, 43.6 g/cm2 for 10 min, and 65.4 g/cm2 for 30min. At the end of pressing, the cloth was removed, and the weight of tofu was recorded. The tofu yield was expressed as 279 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.

grams of tofu per 100 g of soybeans. The tofu was transferred into a plastic bag and stored at 4°C overnight for subsequent measurements.


Transglutaminase-Treated Tofu Making The procedure used for transglutaminase-treated tofu making required some modifications, since the enzyme is not active above 70°C (21). Aliquots of 300 g soybeans were soaked in tap water at 4°C for 9 h to bring the soaked beans weigh to approximately 2.2 times their initial weight. After draining the initial soaking water, tap water was added to the hydrated beans to a final weight of 3300 g to give the water-to-bean ratios of 10:1. The mixtures were performed coarse grinding with a soymilk grinder (Pineapple grinder, Great Yen Electric Food Grinder Co., Ltd. Taipei, Taiwan) then put filtrated okara back into filtrated soymilk. After adding 1 g of antifoaming agent, the okara containing soymilk was heated to 96°C and held at this temperature for 5 min with constant stirring. The boiled okara containing soymilk was cooled to about 65°C , and then CaSO4·2H2O and the MTGase suspended in 50 mL of water were added to this soymilk to give the final CaSO4·2H2O and MTGase concentration used in this soymilk were 0.4% and 5.0 ppm, respectively (w/v). Immediately after the addition of coagulant and enzyme, the okara containing soymilk milk was stirred at speed of 250 rpm for 10 sec, and then incubated for 20 min to form okara containing bean curds. After the incubation, the curd was heated in a hot water bath (90°C) for 30 min to inactive the enzyme. This soybean curd was then broken slightly and transferred into a muslin cloth-lined stainless steel mold (13 x 13 x 5.5 cm3) and pressed at 22 g/cm2 for 10 min, 44 g/cm2 for 10 min, and 65 g/cm2 for 30 min. At the end of pressing, the cloth was removed, and the weight of okara containing tofu was recorded. The tofu yield was expressed as grams of fresh okara containing tofu per 100 g of soybeans. The okara containing tofu was transferred into a plastic bag and stored at 4°C overnight for subsequent measurements. Whole Soybean Tofu Making Three aliquots of 300 g soybeans were soaked in tap water (three times bean weight) at 4°C for 9 h to bring the soaked beans weigh to approximately 2.2 times their initial weight. After draining away the initial soak water, tap water was added to the hydrated beans to a final weight of 3300 g, 3900 g, and 4500 g to give waterto-bean ratios of 10:1, 12:1, and 14:1 (w/w), respectively. At first, the mixtures were performed coarse grinding with a soymilk grinder (Pineapple grinder, Great Yen Electric Food Grinder Co., Ltd., Taipei, Taiwan) and then put okara back into soymilk then followed by fine milling using a wet grinder with a sieve of 425 µm woven wire mesh (Super Fine Grinding machine, Tai Cheer Machinery Enterprise Co., Ltd., Taoyuan, Taiwan) to reduce okara particle size less then 425 µm. After adding 1 g of antifoaming agent, the okara containing soymilk was heated to 96°C and held at this temperature for 5 min with constant stirring. After cooling to 73°C, 50 mL of calcium sulfate solution was added to the mixture to give the final CaSO4·2H2O concentration used in this mixture were 0.4% (w/v), the mixture was stirred at a speed of 250 rpm for 10 sec, and then incubated for 20 min to form okara 280 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.

containing bean curds. The soybean curd was then broken slightly and transferred into a muslin cloth-lined stainless steel mold (13 x 13 x 5.5 cm3) and pressed at 22 g/cm2 for 10 min, 44 g/cm2 for 10 min, and 65 g/cm2 for 30 min. At the end of pressing, the cloth was removed, and the weight of okara containing tofu was recorded. Tofu yield was expressed as grams of tofu per 100 g of soybeans. The okara containing tofu was transferred into a plastic bag and stored at 4°C overnight for subsequent measurements.


Determination of Moisture and Solid Content The moisture content of the tofu and the total solid content of the soymilk were determined according to the procedure of the AOAC (22). Weighed quantities (4-5 g) of samples were oven-dried at 105°C until a constant weight was obtained. Determination of Protein and Solid Contents and Their Recoveries The protein contents in soybean and tofu were determined in triplicate by the micro-Kjeldahl method (22). The solid contents of soybean and tofu were determined by drying a 5 g homogenized sample in an oven at 105°C until constant weight was obtained. Protein recovery in tofu was expressed as the amount of protein in tofu divided by the amount of protein in raw soybean multiplied by 100% on a dry weight basis. The same calculation was applied to solid recovery. Determination of Water Retention Ability (WRA) of Tofu WRA was determined by a modification of the water holding capacity method (WHC) of Puppo and Añón (23). About 5 g (w1) tofu was placed on a cotton clothmembrane maintained in the middle position of a 250 mL centrifuge tube (62 mm × 120 mm). Recording the sample weight after centrifugation at 120 ×g for 5 min at 15°C (w2) and subsequently heating to a constant weight (w3) at 105°C. The WRA of tofu was calculated as following equation: WRA= ((w2-w3)/(w1-w3))×100% Determination of Textural Properties The textural properties of tofu were measured by a texture analyzer (Model TA-XT2, Stable Micro systems, Haslemere, Surrey, UK). A 5 kg load cell was used with the crosshead controlled at 1.5 mm/sec. A cylindrical plunger with a diameter of 35 mm was used to compress the tofu cakes (35 mm dia. × 22 mm ht.) to 50% deformation. Hardness, cohesiveness, gumminess, springiness, and chewiness were calculated using the Textural Profile Analysis curve (24). Hardness was defined as the height of the force peak on the first compression cycle, which was the force necessary to attain a given deformation. The ratio of the positive force areas during the second compression to that under the first compression was defined as cohesiveness. Gumminess was defined as the product of hardness and cohesiveness. The springiness was the degree of recovery to its original height after decompression and accordingly was expressed as the horizontal distance (mm) between the point when the second curve started and 281 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.

the point when the second curve reached a peak. Chewiness was defined as the product of gumminess and springiness. The data were means of 20 replicate measurements at room temperature.


Sensory Evaluation Test (Acceptance Test) The panel was made up of thirty adult males and females who were lifelong tofu consumers and familiar with tofu products. The list of attributes selected by the authors as appropriate for defining the quality of the tofu are appearance, flavor, texture, and overall acceptability. However, the appearance attribute includes color, surface smoothness and homogeneity. The flavor attribute covers aroma and taste. The texture attribute contains firmness and elasticity. And the results were expressed on a 9-point hedonic scale. The sensory scores were 9, like extremely; 8, like very much; 7, like moderately; 6, like slightly; 5, neither like nor dislike; 4, dislike slightly; 3, dislike moderately; 2, dislike very much; 1, dislike extremely. Samples for sensory evaluation were cut into cubic samples (2.0 cm) and cooked in boiling water for 5 min, then removed out and placed on sieves to drain followed by keeping at room temperature before evaluation. All samples were coded and always presented in a randomized arrangement. Data Analysis All results were analyzed by analysis of variance (ANOVA) using the general linear model (25). Duncan’s multiple range test was used to determine differences among the samples. Significant levels were defined as probabilities of 0.05 or less. All processing treatments were in triplicate.

Results and Discussion The Effects of Grinding-Treatment on Whole-Soybean Tofu Quality Tofu of good quality is judged in terms of appearance, texture, aroma, taste and mouthfeel and high yield. Smoothness and texture are important attributes influencing acceptability of tofu by consumer. While, the yield of tofu is an important consideration for tofu manufactures to select processing conditions. Table 1 shows the effects of okara particle size on the quality of whole-soybean tofus prepared by coarse milling or fine milling (reduced okara particle size less then 425 µm). As compared with conventional tofu, the employ of okara caused significant increase in soymilk solid content, protein and solid recoveries for two kinds of whole-soybean tofu, hence, caused the increase in tofu yield. Regarding the increase in moisture content of tofu, it resulted from the high water binding ability of okara. Ma et al. (26) found that protein in okara possessed good water binding properties and was comparable to that of commercial protein source, in addition, polysaccharide in okara might be also responsible for the high water hydration ability of okara (27). However, the employ of okara significantly decreases the WRA of tofu (Table 1), result from okara destroys the uniformity of microstructure of tofu. In our previous studies (28) we suggested that the tofu 282 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.


had the better uniform and homogeneous microstructure, resulted in the better WRA. In addition, Puppo and Añón (23), who also showed that a protein gel with a homogeneous and fine structure gave high WRA as compared to the gel with a nonhomogeneous structure, which had a high degree of syneresis. By the way, the whole-soybean tofu treated with coarse milling was not solidified by the CaSO4. 2H2O, even if a gel matrix was formed, it was very fragile and tended to collapse when subject to slight shaking. However, the whole-soybean tofu treated with fine milling was observed that formed a stable and firm tofu gel after addition of calcium sulfate.

Analysis of Quality and Texture Properties for Transglutaminase Treated Tofu The coagulation of soymilk is an important step during tofu manufacturing. Salts (e.g. CaSO4, CaCl2, MgCl2 and MgSO4) and acid (glucono-δ-lactone; GDL) have been used as the coagulant to prepare tofu. Besides those coagulants, MTGase (EC .2.3.2.13) enzyme could also result in the coagulation of soymilk to produce tofu, and the formed tofu is more retort-resistant as compared with those tofus induced by other kinds of coagulants (29). MTGase is reported that has ability to catalyze the formation of covalent cross-linking between soy proteins in soymilk, besides, Kwan and Easa (30) pointed out that tofu treated with MTGase could reduce retort-induced syneresis of GDL tofu. Since the whole-soybean tofu treated with coarse-milling couldn’t solidified by traditional coagulants, MTGase was used to induce gel formation of this whole-soybean tofu. As shown in Table 2, MTGase significantly increased WRA and protein recovery of “whole-soybean tofu” manufactured through coarse milling. Apparently, the coagulation of okara containing soymilk by means of MTGase addition could increase the WRA and consequently result in low syneresis and less loss of soluble protein and other soluble substance. These events would seem to account for higher protein recovery. Table 3 shows the impact of MTGase on the textural properties of “wholesoybean tofu “treated with coarse-milling. As compared with conventional tofu, the employ of okara significantly decrease the springiness and cohesiveness of tofu without MTGase treated. The decrease in cohesiveness resulted from the presence of okara causing less uniform and homogeneous microstructure. These observations were in agreement with our previous findings (28) that tofu with a less intensive network give less cohesiveness. Meanwhile, MTGase treatment was expected to cause significantly increases in hardness, springiness, cohesiveness, gumminess and chewiness of tofu texture (Table 3). The much firmer texture was due to excessive formation of cross-linking (21), while subsequently found to decrease the acceptability of tofu by consumer. Besides, the coarse texture couldn’t meet the requirement of consumers.

283 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.

Table 1. Effect of particle size of okara on the moisture, WRA, protein recovery, solid recovery and tofu yield of “whole-soybean tofu”a Protein Recovery (%)

Solid Recovery (%)

Tofu yield (g tofu/ 100 g soybean)

77.2 ± 0.1 a

70.9 ± 0.7 b

55.9 ± 0.8 b

253.3 ± 2.9 c

84.3 ± 0.8 b

52.4 ± 0.7 c

79.3 ± 0.9 a

78.8 ± 3.9 a

451.1 ± 1.5 b

86.2 ± 0.4 a

55.3 ± 1.5 b

80.5 ± 1.0 a

76.1 ± 1.8 a

495.4 ± 6.5 a

Soymilk Solid Content (%)

Moisture (%)

6.0 ± 0.0 b

80.5 ± 0.5 c

Coarse milling

8.0 ± 0.1 a

Fine milling

8.0 ± 0.1 a

Tofu variety

Conventional tofu

WRA (%)

Wholesoybean tofu Downloaded by UNIV OF GUELPH LIBRARY on June 24, 2012 | http://pubs.acs.org Publication Date (Web): December 14, 2010 | doi: 10.1021/bk-2010-1059.ch018

b

a Mean scores bearing the same letters among the same column are not significantly different (p < 0.05). b The tofu made at the water-to-bean ratio of 10:1 and with 0.4% calcium sulfate in soymilk.

Table 2. Effect of transglutaminase on the moisture, WRA, protein recovery, solid recovery and tofu yield of “whole-soybean tofu” a Protein Recovery (%)

Solid Recovery (%)

Tofu Yield (g tofu/ 100 g soybean)

77.2 ± 0.1 a

70.9 ± 0.7 c

55.9 ± 0.8 b

253.3 ± 2.9 b

84.3 ± 0.8 a

52.4 ± 0.7 c

79.3 ± 0.9 b

78.8 ± 3.9 a

451.1 ± 1.5 a

83.5 ± 0.8 a

70.4 ± 1.8 b

83.7 ± 1.0 a

83.2 ± 4.0 a

453.2 ± 3.9 a


Moisture (%)

6.0 ± 0.0 b

80.5 ± 0.5 b

Without mtgase

8.0 ± 0.1 a

With mtgase

8.0 ± 0.1 a

Tofu Variety

Conventional tofu

WRA (%)

Whole-soybean tofu b

a Mean scores bearing the same letters among the same column are not significantly different (p < 0.05). b This whole-soybean tofu was manufactured with coarse milling.


Table 3. Effect of transglutaminase on the textural properties of “whole-soybean tofu” a Tofu Variety

Hardness (Kg)

Springiness (mm)

Cohesiveness (mm)

Gumminess (Kg)

Chewiness (Kg.mm)

0.71 ± 0.11 c

9.76 ± 0.04 b

0.45 ± 0.02 a

0.32 ± 0.02 b

3.11 ± 0.25 b

Without MTGase

1.06 ± 0.09 b

7.74 ± 0.33 c

0.27 ± 0.01 c

0.29 ± 0.03 b

2.22 ± 0.25 b

With MTGase

3.68 ± 0.13 a

10.59 ± 0.18 a

0.38 ± 0.03 b

1.40 ± 0.12 a

14.81 ± 0.98 a

Conventional tofu Whole-soybean tofu


b

a Mean scores bearing the same letters among the same column are not significantly different (p < 0.05). b This whole-soybean tofu was manufactured through coarse milling.

Effects of Water-to-Bean Ratios on the Quality and Texture of “Whole-Soybean Tofu” Manufactured through Fine Milling As mentioned earlier, the whole-soybean tofu manufactured through fine milling could form a stable and firm tofu gel just by means of calcium sulfate addition. As compared with coarse milling, this tofu gave better homogeneous appearance and smoother texture. Table 4 shows the tofu made with water-to-bean ratio of 12:1 had the maximal protein and solid recoveries, and the best WRA as well as the maximal tofu yield. As stated previously, the employ of okara resulted in increase in moisture content and subsequently caused decrease in tofu hardness (Table 5). In addition, okara might have a role to destroy the uniformity of tofu microstructure owing to its poor dispersion in soymilk, in turn, consequently, resulted in less cohesiveness. The results of Table 5 indicated that hardness, springiness, cohesiveness, gumminess, and chewiness decreased as the water-to-bean ratio increased. However, as compared with conventional tofu, the whole-soybean tofu treated with the water-to-bean-ratios in the range of 10-14, all possessed softer, less elastic and less chewy texture (Table 5). Figure 1 shows the surface and cross-section photographs of conventional tofu and whole-soybean tofu manufactured via fine milling as we suggested above. The whole-soybean tofu was darker in color, had coarse surface and coarse crosssection, and rough mouthfeel as compared to conventional tofu. As stated earlier, Aburage and Kori- tofu were two tofu analogues, both with coarse appearance and rough mouthfeel but chewy texture. Therefore, we suggest this whole-soybean tofu could be served in following ways: cooked in soup, fried in oil (close to Aburage tofu), or further developed into Kori-tofu.



Table 4. Effect of water-to-bean ratios on the moisture, WRA, protein recovery, solid recovery and tofu yield of “whole-soybean tofu”a,b Water:Bean Ratio


Moisture (%)

10

8.0 ± 0.1 a

86.2 ± 0.4 a

55.3 ± 1.5 b

80.5 ± 1.0 c

76.1 ± 1.8 b

495.4 ± 6.5 b

12

7.2 ± 0.1b

85.7 ± 0.1a

60.9 ± 1.1 a

87.4 ± 0.5 a

80.7 ± 0.6 a

507.1 ± 6.1 a

14

6.0 ± 0.0 c

86.0 ± 0.3 a

59.9 ± 0.9 a

85.3 ± 0.5 b

78.0 ± 0.2 ab

501.1 ± 2.7 ab

WRA (%)

Protein Solid Recovery Recovery (%) (%)

Tofu Yield (g tofu/ 100 g soybean)

a Mean scores bearing the same letters among the same column are not significantly different (p < 0.05). b This whole-soybean tofu was manufactured through fine milling.

Table 5. Effect of water-to-bean ratios on the textural properties of “whole-soybean tofu” a Water:Bean Ratio

Hardness (kg)

Springiness (mm)

Cohesiveness (mm)

Gumminess (kg)

Chewiness (kg.mm)

0.71 ± 0.11 a

9.76 ± 0.04 a

0.45 ± 0.02 a

0.32 ± 0.02 a

3.11 ± 0.25 a

10

0.62 ± 0.04 b

6.97 ± 0.65 b

0.35 ± 0.02 b

0.22 ± 0.01 b

1.53 ± 0.02 b

12

0.59 ± 0.09 b

6.47 ± 0.40 bc

0.35 ± 0.02 b

0.21 ± 0.02 b

1.36 ± 0.11 b

14

0.55 ± 0.05 b

5.97 ± 0.25 c

0.30 ± 0.04 c

0.17 ± 0.01 c

0.99 ± 0.10 c

Conventional tofu Whole-soybean tofu b

a Mean scores bearing the same letters among the same column are not significantly different

(p < 0.05).

b

This whole-soybean tofu was manufactured through fine milling.



Figure 1. Photograph of conventional tofu (A) and whole-soybean tofu manufactured via fine milling (B).

Sensory Evaluation Study In this acceptance test of this new tofu, sample was served in cooked form, in the future study we would like to analyze the acceptance in the Aburage and Kori-tofu form. Tofu samples were evaluated by a panel for appearance, flavor, texture and overall acceptability on a 9-point hedonic scale. Conventional tofu and whole-soybean tofu were evaluated, and the results are shown in Table 6. With the employ of okara, there were trends of decrease acceptance for appearance, texture, and overall acceptance except for flavor. Appearance acceptance decreased in whole-soybean tofu for the sake of darker color and less smoother surface, while increase in flavor acceptance resulted from having a savory cooked flavor. A survey revealed that cooked okara could contribute pleasant cooked flavor to puffed okara/rice cake (31) supported our results. Regarding to texture acceptance, preference varies from place to place, in China and Taiwan there is a preference for a firmer and chewier mouthfeel (20, 32, 33). Therefore, the hardness and chewiness measured by texture analyzer were in agreement with our sensory evaluation result (Table 5, Table 6).


Table 6. Nine point scale sensory evaluation of conventional tofu and whole-soybean tofu a

Conventional tofu Whole-soybean tofu b

Overall Acceptability

Flavor

Texture

6.8 ± 1.3 a

6.3 ± 1.2 b

5.6 ± 1.4 a

6.5 ± 1.3 a

6.5 ± 1.4 b

6.5 ± 1.4 a

5.3 ± 1.2 b

6.2 ± 1.4 b

Appearance

Tofu Variety


a Mean scores bearing the same letters among the same column are not significantly different (p < 0.05). b This whole-soybean tofu was made at the water-to-bean ratio of 12:1 and fine milling.

Table 7. The general compositions of soybeans, tofu, okara and whole-soybean tofu Solids

a

Sample

Moisture (%)

raw soybean

10.1 ± 0.5

conventional tofu

lipid (%)

ash (%)

carbohydrate (%)

40.6 ± 2.1

22.0 ± 1.9

6.1 ± 0.5

23.7 ± 0.3

7.6 ± 2.3

80.5 ± 2.5

50.2 ± 0.5

34.1 ± 2.1

7.2 ± 0.3

8.5 ± 0.4

0.0 ± 0.0

okara

79.2 ± 3.1

22.5 ± 2.1

8.0 ± 2.1

5.0 ± 0.4

45.2 ± 4.1

19.3 ± 0.3

wholesoybean tofua

86.3 ± 2.6

46.4 ± 3.1

23.2 ± 1.8

6.4 ± 0.2

14.9 ± 2.0

9.1 ± 0.6

protein (%)

crude fiber (%)

This whole-soybean tofu was made at the water-to-bean ratio of 12:1 and fine milling.

Food Chemical Analysis of Soybean, Okara, Tofu, and Whole-Soybean Tofu Results of the food chemical analyses are presented in Table 7. The conversion of soybeans into tofu and okara led to the following changes in the proximate composition, protein and lipid were concentrated in tofu, while carbohydrate and crude fiber were almost concentrate in okara. Regarding the whole-soybean tofu, as compared with conventional tofu, the employ of okara was found to result in the increase in carbohydrate and crude fiber content. While, as compared with raw soybean, there was a decrease in carbohydrate content that might be due to the loss of soluble carbohydrate, including monosaccharides and oligosaccharides, during tofu-manufacturing. Besides, the poor WRA might be the reason to cause the loss of soluble carbohydrate. In conclusion, okara is the byproduct during soymilk or tofu manufacturing. It’s high in nutrients and possesses great potential to be applied to functional human food. The object of this study was to develop whole-soybean tofu or its analogue 288 In Chemistry, Texture, and Flavor of Soy; Cadwallader, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.


and could commercialize it in the future, thus, it would improve human health and decrease the risk levels of ecological damage. In this study, we found that wholesoybean tofu with fine-milling could form a stable firm gel just after addition of calcium sulfate, while tofu with coarse milling couldn’t be successful made until by means of MTGase addition. On the other hand, MTGase treatment was expected to increase significantly hardness, springiness, cohesiveness, gumminess and chewiness of tofu texture, as well as WRA. Regarding to the whole-soybean tofu with fine milling, it was found that tofu made with water-to-bean ratio of 12:1 gave the maximal protein and solid recoveries, as well as the maximal tofu yield. However, this whole-soybean tofu possessed softer, less chewy texture, and coarse appearance. Therefore, MTGase will be still needed to modify tofu texture in the following research. This whole-soybean tofu could be served in the following ways: cooked in soup, fried in oil, or further developed into Kori-tofu. Above all, whole-soybean tofu was rich in fiber and low in fat, it could be considered as a healthy food.

Acknowledgments The authors thank the National Science Council of the Republic of Chins, Taipei, Taiwan, for the financial support of this research under the project NSC89-2214-E-002-076 and NSC-90-2214-E-002-028.

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Development and Quality of Tofu Analogue Prepared from Whole

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