Influence of Tannin on Phaseolus vulgaris Protein Digestibility and Quality

The influence of tannin on protein digestibility and quality of black beans was evaluated using an enzyme‐ Tetrahymena thermophila bioassay. In vitro digestibility and t‐PER ( Tetrahymena ‐based PER) were inversely related to tannin content. Bioavailability, expressed by Tetrahymena growth, of black bean globulin G 1 in the presence of black bean condensed tannins correlated well (r=0.95) with the in vitro digestibility of the protein. Black bean condensed tannins complexed readily with black bean globulin G 1 to form insoluble precipitates from pH 2.0 to pH 8.0. Bean tannin‐G 1 precipitates, at tannin‐to G 1 ratios of 0.55 or greater, were resistant to pepsin digestion at pH 2.0. Digestion of bean tannin‐G 1 precipitates was 69–74% at pH 8.0, using a multienzyme system of trypsin, chymotrypsin and peptidase.