The effect of microwave roasting on soybean protein composition and components with trypsin inhibitor activity

Abstract

The effect of microwave roasting on protease inhibitor activity and Soluble protein content and composition in cracked soybeans was investigated in relation to the duration of treatment. Soybeans of Hodgson var. were cracked to 1/6-1/8 of the size of whole bean, dehulled and were exposed to microwaves at a frequency of 2.450 MHz. Soluble protein content of hexane defatted samples were determined and PAGE, SDS-PAGE and densitometric analyses were used to determine the change of major soybean protein subunits as a function of roasting time. Residual protease inhibitor activities and isoinhibitor composition were also determined. Microwave treatment is an effective way for inactivation of protease inhibitor activity in cracked soybeans. Roasting for only two minutes reduced the trypsin inhibitor activity to 13.33% of the initial value. Both types of inhibitors, Kunitz (KTI) and Bowman-Birk (BBI) were responsible for residual inhibitor activity. The duration of microwave roasting had strong influence on soluble protein content and polypeptide composition. Microwave treated samples were characterized by dominant content of glycinin, and high stability of acidic (-A(1,2,3)-, -A(5)-) and basic (-B-1,B-2,B-3,B-4-) glycinin subunits were established.