An advance for removing antinutritional protease inhibitors: Soybean whey purification of Bowman-Birk chymotrypsin inhibitor by combination of two oppositely charged polysaccharides

Abstract

Two successive and selective coacervations induced by chitosan (Ch) and carrageenan (CG) were applied to remove antinutritional protease inhibitors and purify Bowman–Birk protease inhibitor (BBI) from soybean whey. At the first coacervation induced by Ch (66.7, 200, and 510kDa), only Kunitz trypsin inhibitor (KTI) and BBI complexed with Ch were extracted, while β-amylase and soybean agglutinin remained in supernatant. The binding constants for the interaction increased on the order Ch-66.7<Ch-200<Ch-510. At the second selective complexation, we observed a competitive binding behavior between KTI/BBI and CG. At a mixing weight ratio of 3:1 (pH 3.0 for ι-CG, and pH 3.11 for λ-CG), the preferential binding of KTI to CG led to the single enrichment of BBI in the supernatant. Our results indicated that the purified BBI was a good source for further study of its anti-carcinogenic properties, due to its high bioactivity (669.5U/mg chymotrypsin-inhibitory activity and 2260U/mg trypsin-inhibitory activity).