Effect of Soybean Varieties on the Yield and Quality of Tofu l H. L. WANG, E. W. SWAIN, and W. F. KWOLEK, Northern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Peoria, IL 61604; and W. R. FEHR, Department of Agronomy, Iowa State University, Ames, IA 500 II ABSTRACT Cereal Chern. 60(3):245-248 Tofu was made on a laboratory scale from five U.S. and five Japanese high protein content also produced tofu with a higher ratio ofprotein to oil soybean varieties grown under the same environmental conditions. With than did varieties with smaller amounts of protein. The yield of tofu was one exception, all the tofu samples had a bland taste. fine texture, and positively correlated with protein recovery during processing. but not with creamy white color. Weber variety with a black hilum yielded tofu with a the protein content of the beans. The hardness of tofu varied according to less attractive color. Differences observed among the 10 varieties were not \vater content. Conditions in processing tofu greatly affect yield and quality. attributable to the country of origin. Protein contents of soybeans and the Varietal differences affected the composition and color of tofu. Varieties resultant tofu (dry basis) were positively correlated. Soybean varieties with that have a light hilum and high protein content are preferred. Tofu, a traditional oriental soybean food composed principally tofu producers, western consumers prefer tofu with a firm, chewy of protein and oil. is growing rapidly in popularity in the West. texture. According to data from the Soyfoods Center (Shurtleff 1982). the For centuries. the process of making tofu has been controlled by number of nonoriental tofu producers in North America rose from tradition and long experience: without the benefit of scientific oin 1975 to 167 in 1981. More than 11.000 tons ofsoybeans are used knowledge, tofu "craftsmen" have skillfully carried on the process. yearly in making tofu in the United States. Although the bulk of the In recent years. studies have been made on gel formation of soybean crop is still used for animal feeds and oil, the use of whole proteins isolated from defatted soybean meal as well as from water soybeans for human consumption is increasing steadily. extract of whole soybeans. Processing conditions, such as type and Tofu is made by precipitation of the proteins with a calcium or concentration of coagulants, temperature, mode of mixing. and magnesium salt from a hot-water extract of whole soybeans. It is pressure applied, that affect the quality and quantity of gel usually sold in the form of a wet cake with a creamy white color. formation in tofu have been investigated (Lu et al1980, Saio 1979. smooth fine texture. and bland taste. Tofu is a highly hydrated. Tsai et al1981. Wang and Hesseltine 1982, Watanabe et aI1960). gelatinous product. Its water content can be varied to produce an Scientists have just begun to comprehend the centuries-old process array of tofu with different characteristics. The typical type in the of making tofu. Orient has an approximate composition of 85% water and 7.5% In addition to processing conditions, soybean variety has been protein (Smith et al 1960, Table of Taiwan Food Composition reported to affect the yield and quality of tofu. Watanabe et al 1971, Tsai et al 1981). This type of tofu has a soft, cheeselike texture (1960) found that Japanese varieties were more desirable than U.S. but is firm enough to retain its shape after slicing. Tofu with water varieties. But Smith et al (1960) reported that the most important content as high as 87-90% (Standard Tables of Food Composition differences between Japanese and U.S. soybeans, as viewed 1954. Tsai et al 1981) and a smooth, fragile texture is especially according to Japanese custom, were in texture and color of the tofu popular in Japan. In China, however, many types of firm, chewy produced from them. Although yield and composition of tofu tofu products with water content as low as 50-60% are popular. varied with soybean variety. the average yield from U.S. soybeans Tofu in U.S. markets contains 75-80% water. According to U.S. was the same as that from Japanese beans. However. the same authors cautioned that the differences in composition of beans probably reflected the effect of location as much as varietal :Joint contribution: USDA, Agricultural Research Service. Northern Regional differences. More recently, Skurray et al (1980) used 15 soybean Research Center. Peoria. IL: and Journal Paper J-I0815 (Project 2475) of the- Iowa Agriculture and Home Economics Experimental Station, Ames 5001 I. varieties grown under the same agricultural conditions for making Reference to a company or product does not imply approval or recommendation of tofu and found that the amount ofcalcium used had a greater effect the product by the USDA to the exclusion of others that may be suitable. on the quality of tofu than did the variety of soybeans. This article is in the public domain and not copyrightable. It may be freely Nevertheless, the problem persists in selecting the most suitable reprinted with customary crediting of the source. The American Association of variety for making tofu. Cereal Chemists. Inc .. 1983. In this study, soybean varieties originating in the United States Vol. 60. No.3. 1983 245 and Japan and grown in the same location under the same Analytical Methods environmental conditions were used to determine varietal Moisture content was determined by drying samples to constant variability in making tofu. weight at I 10° C. Protein and oil contents of beans were measured by near-infrared reflectance. Protein and oil contents of freeze­ MATERIALS AND METHODS dried samples of soy milk and tofu were determined by micro­ Kjeldahl analysis (AOAC 1970) and hexane extraction, Soybean Samples respectively. Ten soybean varieties-five U.S. and five Japanese-were Tofu preparation was done twice for each sample from each grown in two replications ofa randomized complete block design at replicate. Data were examined by analysis of variance. Variations Ames, lA, in 1981. The five Japanese commercial varieties were attributable to origin and varieties within country of origin were sent to Iowa from Hokkaido, Japan. in 1980. Seed harvested from estimated and tested for significance. Correlation coefficients were Iowa in 1980 was used to plant the same experiment in 1981 to determined to measure the degree and significance of association eliminate any possible effect of seed source. The five U.S. varieties among the various measurements. are commercially grown in Iowa. The Vinton variety was released specifically for food uses because of its high protein content and RESULTS AND DISCUSSION large seed. It is not recommended for planting, except when the farmer has a contract for sale of the beans to someone who sells Tables I and II summarize the results statistically. Means are the soybeans to food processors, primarily tofu manufacturers. Yield average of four measurements, two for each replicate of the variety, of Vinton is lower than that of other available varieties. except those for protein and oil contents of the beans, which represent the average of two measurements, one for each replicate. Preparation of Tofu Tofu was prepared by the method of Wang and Hesseltine Origin of Soybean Varieties (1982). Fifty grams of beans was washed and soaked in water at Using the same coagulation conditions, satisfactory tofu was room temperature (20-22° C) for 16 hr to reach complete made from all soybean samples. Significant variation among hydration. The soaked beans were drained, rinsed, and homo­ varieties was observed for protein and oil content ofthe beans. size genized for 2 min in a Brinkman homogenizer with enough added of the beans (weight of 100 beans), amount of water absorbed at water to give a water-dry beans (before soaking) ratio of 10: 1 complete hydration, protein concentration of soy milk. fresh tofu (weight basis). The slurry was brought to a boil and kept at boiling yield, tofu protein on dry basis. and tofu hardness, but none of temperature for 15 min. The hot slurry was then filtered through these differences was associated with the origin of the soybean four-layer cheesecloth to separate the milk from the pulp. Pressure varieties (U.S. vs Japanese). was applied to the pulp with a press to harvest the maximum amount of milk. When the milk was cooled to about 70°C. 400 ml Tofu as Affected by Physical Properties of Soybeans was forcefully poured into a calcium sulfate (CaS04'2H:O, Terra Tofu prepared from all soybean varieties tested had a bland taste, Alba) suspension to achieve a mixing action. The calcium sulfate smooth texture. and creamy white color. However. tofu made from suspension consists of40 ml of water (10% volume of the milk) and soybeans with a black hilum (Weber variety) had a less attractive 1.52 g of CaS04' 2H:O, so that the final concentration of the salt in color. with a gray cast over the traditional creamy white. the milk is 0.02M. After settling for 10 min, the curds were At complete hydration, the amount of water absorbed by the transferred to a cheesecloth-lined wooden box (7.5 X 7.5 X 7.5 cm) beans was approximately 1.3 times the original bean weight. Larger and pressed by placing weight (10 g/ cm:) on the top for I hr. beans absorbed more water in proportion to size, but neither the size of the beans nor the amount of water absorbed by the beans Texture Evaluation was significantly associated with the yield and quality of tofu. The hardness of tofu was evaluated with an Instron Universal testing machine as previously described (Wang and Hesseltine Composition of Tofu as Affected by Soybean Variety 1982).