The extractability of winged bean (Psophocarpus tetragonolobus) seed trypsin inhibitors

Abstract

AbstractThe extractability of winged bean (Psophocarpus tetragonolobus) seed trypsin inhibitors by aqueous salt solution varies with pH as well as the ionic strength of the extraction medium. With a high ionic strength extraction medium, the extractability of the seed trypsin inhibitors increases with rising pH. With a low ionic strength extraction medium, however, a region of minimum extractability of trypsin inhibitors was observed at pH 4. At pH above 7, the same maximum amount of trypsin inhibitors (1.47 million inhibitor units (i.u.) per 100 g of seed meal) was extracted with both high and low ionic strength extraction media. The solution characteristics of winged bean seed proteins exhibited similar trends. Ninety‐five per cent of the extracted seed trypsin inhibitors could be precipitated from 30–70% saturated ammonium sulphate solutions. The winged bean seed trypsin inhibitors isolated by ammonium sulphate fractionation lost all inhibitory activity when heated at 100°C for 10 min at alkaline pH.