The influence of storage conditions on soybean components and its relation to soymilk and tofu quality
The objective of this study was to observe the changes that occur during soybean storage and its effects on soymilk and tofu quality. Three food grade soybeans, Vinton 81, IA2032 LS, and Proto, from the 2002 and 2003 crop years were used in this study. The soybeans were stored at temperatures of 200C, 300C, 400C, with two humidity conditions, 32 and 75% RH, and were evaluated every 3 months. The difference in the lengths of soybean storage was based on failure of the extracted soymilk to coagulate, which occurred at the highest temperature and humidity storage condition, at 6 months in 2002, and at 12 months in 2003. The soybeans were evaluated for moisture, protein and oil, color, total and soluble oxalates, antioxidant capacity, and soluble sugars. The soybeans were subsequently processed into soymilk and tofu using the traditional Japanese method, and were evaluated for yield, color and texture. Soybean oxalate content was not affected by different storage conditions, although there was a difference between total oxalate content and soybean cultivars. The oxalates did not make a difference in affecting tofu yield or texture. Antioxidant capacity of soybeans was found to increase when stored at a high temperature and humidity condition. Glucose was only found under high temperature and humidity storage conditions. With increased storage time, temperature and humidity, soybeans had lower Hunter L values and browning of the soybean seed coat was observed. This in turn carried over into soymilk and tofu produced from these soybeans, and was also observed by the gradual increase in + a values with increasing temperature and humidity. Soymilk solids level is a good indicator of its ensuing tofu quality. There was a very distinct color difference in different soybean cultivars at all storage conditions. Therefore, color can be used as a predictor of soybean storage conditions and its resulting product quality.