45G-4 |
Changes of oxalate levels in soybeans during storage |
J. Y. L. KUAN, Food Science and Human Nutrition, Iowa State University, 2312 Food Sciences Building, Ames, IA 50011 and L. A. Wilson, Dept. of Food Science & Human Nutrition, Iowa State Univ., 2541 Food Science Bldg., Ames, IA 50011-1061. Oxalate is a salt or ester derivative of oxalic acid, which is naturally occurring in plants, vegetables and nuts. Oxalates are capable of forming an insoluble salt with calcium and thus interfere with its absorption by the body. Human consumption of soybeans and products made from them has been increasing of late, due to its many nutritional benefits. Despite its nutrient content, the nutritional consequences of the oxalate content of soybeans and it’s binding with calcium have been overlooked due to the lack of study on the oxalate content of soybeans and other legumes commonly consumed. Soy foods contain about 10mg of calcium oxalate per serving. Studies have shown that storage affects the tofu yield with the amount of coagulant added to the soymilk. The objective of this study is to determine whether the oxalate content is affected by storage conditions such as time, temperature and humidity, thus influencing the level of coagulant needed for optimum tofu yield. Soybean samples were ground, filtered and incubated before being assayed using a modified protocol from the SIGMA Urinalysis Diagnostics Kit Procedure No. 591. Each sample was assayed for total, soluble and insoluble oxalates using the absorbance data. The soybeans were stored for 8 months in both a dry condition at temperatures of –20°C, 4°C and 25°C and wet condition at –20°C. The level of soluble oxalates remained constant through 6 months of storage at all treatments. However, by 8 months of storage, soluble oxalate levels increased significantly for all treatments. Within that group, the dry soybeans stored at –20°C had the highest increase. Insoluble oxalates had very insignificant changes for all treatments. The results could be used to determine the optimum storage conditions based on the level of oxalates to improve tofu yields.
Session 45G, Fruit & Vegetable Products: Vegetables (Fresh)
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