36E-23 |
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J. Y. L. KUAN and L. A. Wilson. Dept. of Food Science and Human Nutrition, Iowa State Univ., 2312 Food Sciences Building, Ames, IA 50011 Post-harvest modification of soybeans is very pronounced in the summer months, especially during storage and transporting across continents. Over prolonged storage, soybean seed quality and quality of edible products made thereof decreases. The objective of this study was to observe the biochemical changes that occur during soybean storage and its effects on soy food quality, particularly soymilk and tofu. Three different soybean cultivars from two crop years were stored at different temperature (20, 30, 40o C) and humidity (75% RH, 32% RH) combinations for 0-12 months. Soybeans were analyzed for color (HunterLab), oxalates (enzymatic assay), antioxidants (PhotoChem), sugars (HPLC), and processed into soymilk and tofu (Japanese method). With increased storage time, temperature and humidity, soybeans had lower Hunter L values (darker), as browning of the soybean seed coat was observed. This in turn carried over into soymilk and tofu produced from these soybeans. At elevated temperatures and humidities, most proteins have degraded, confirmed by the soymilk not coagulating after 6-9 months of storage. Environmental factors and genotype accounted for the differences in oxalate concentration in the soybeans. Antioxidants in soybeans, when stored at a higher temperature and humidity, had an increased concentration, which could be attributed to the conversion of isoflavones (an antioxidant) from the malonyl to aglycone form. Soybean soluble sugars, although present in small amounts, are important, especially oligosaccharides and reducing sugars. Glucose was only found under high temperature and humidity storage conditions, which suggests complex oligosaccharide breakdown. Sucrose remained relatively stable at all storage conditions, indicating that sucrose was not consumed in Maillard browning reactions. Biochemical changes were also observed within each cultivar based on crop year and environmental factors. Based on these results, storing soybeans under low moisture and temperature conditions are recommended in order to have quality soy products with good functional properties and economic viability.
Session 36E, Fruit & Vegetable Products: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |