Thermal stabilization of the trypsin-inhibitor by crushing -flaking of soybeans

Abstract

The author had evaluated the digestion of proteins of parched soybeans by trypsin and observed high digestibility after parching of intact whole soybeans but very low digestibility after parching of crushed soybeans, previously this was because the trypsin inhibitor (TI) that is present in intact whole soybeans is readily inactivated by parching, whereas the TI in crushed soybeans has become thermostable and is not inactivated by parching. In this paper, changes in TI activity after tissue destruction and heating of soybeans were evaluated. The TI activity in parched (150°C, 20 min.) intact whole soybeans was decreased by heat to about 1/20 of the initial level. On the other hand, TI activity in soybean flour or soybean flakes was less inactivated with a higher degree of tissue destruction. The TI activity in parched soybean flour with a particle diameter less than 1 mm was similar to that in raw soybeans. Proteins in raw soybeans, parched intact whole soybeans, and parched soybean flour were digested with trypsin. The digestion rate increased with the added amount of trypsin even when the amount of trypsin was lower than the unit amount of the residual TI. The digestion rate reached about 50% with an amount of trypsin the same as the unit amount of TI and increased thereafter in proportion to the added amount of trypsin, being the maximum with an amount of trypsin twice the unit amount of TI.