Effect of tissue destruction of soybean seeds on the inactivation of trypsin-inhibitor by heating in water

Abstract

It is well known that trypsin- inhibitor (TI) is readily inactivated by heating soybeans in boiling water. Based on the previous results that much better digestibility of parched soybean proteins by trypsin was attained with intact soybeans than with crushed ones due to TI stabilized in crushed soybeans, an investigation was conducted whether or not the similar results are obtained by heating intact or crushed- soybeans in boiling water. TI in intact- soybeans was mostly inactivated after heating 20 min in boiling water, whereas TI in crushed- soybeans was still active under the same conditions. It seems that the higher the tissue destruction of soybeans, the lower the rate of TI inactivation. In the case of soybean flour, TI activity of more than 2000 unit per gram was remained. In Japanese dishes, soybeans are thoroughly softened in boiled water under pressure to increase both digestibility and flavor. The above results, however, suggest that heating intact soybeans in boiling water for 10 to 20 min is sufficient as far as the digestibility of soybean proteins is concerned.