Deterioration of Soybean during Storage under High Moisture and Temperature

Abstract

U.S. soybeans (1975 crops, IOM) were stored under the conditions of 40°C and R.H. 75.2% for around one month to investigate on the changes of the quality as well as suitability for making Tofu. The following results were obtained; (1) Nitrogen Solubility Index (NSI) and solubility of solid decreased, while organic and fatty acids increased as storage period progressed. The pH of the water extract slightly shifted to acidic range. (2) The levels of solid, nitrogen, sugar and phosphorus in the soaking water in which stored soybeans were soaked overnight definitely increased, while solid and nitrogen in the soybean milk prepared from the soaked soybeans decreased, resulting in the formation of softer Tofu. This fact was principally due to the reduction of soymilk concentration resulted from the reduction of extractability from soaked soybeans, (3) The reduction of protein extractability of the stored soybeans was nearly restored by the extraction with dilute alkaline or/and mercaptoethanol solution or even repeated water extraction. (4) The protein components extracted with water from the soybeans after storage consisted of higher ratio of 7S to 11S proteins, when compared with those before storage.