Kunitz trypsin inhibitor in soybean: contribution to total trypsin inhibitor activity as a function of genotype and fate during processing

Abstract

Detrimental effects of trypsin inhibitor activity (TIA) in soybean on human health have been attributed to Kunitz trypsin inhibitor (KTI) polypeptide. Literature is replete with reports pertaining to TIA in soybean seeds, however, the studies on the contribution of KTI polypeptide to total TIA have not been carried out. Further, very limited information is available on the quantitative changes occurring in this polypeptide due to different processing methods. In the present investigation, KTI polypeptide in soybean seeds was resolved by native polyacrylamide gel electrophoresis (PAGE) and substantiated by western blotting. Densitometry was employed to quantify KTI polypeptide in 102 soybean genotypes and assess the inactivation of this polypeptide due to boiling, autoclaving, microwave irradiation and sprouting. KTI concentration exhibited wide genetic variation, ranging from 0.07 to 15.9 mg/g soy flour, which corresponded to 1.0–79.8% of total TIA. Boiling and autoclaving for 15 min both resulted in complete inactivation of KTI. Microwave irradiation induced significantly higher reduction for KTI in soaked than dry seeds. Sprouting for 4 days caused 71.4% inactivation of KTI. The study showed that KTI contribution to total TIA was genotype-dependent and the inactivation of this polypeptide was a function of processing methods.