Effect of Condensed Grape Tannins on the In Vitro Activity of Digestive Proteases and Activation of Their Zymogens

Only at concentrations substantially higher than those likely to occur in human diets did grape tannins have a significant adverse effect on the in virro digestion of bovine serum albumin (BSA). The activities of pepsin and chymotrypsin were at such levels (concentrations greater than 0.1%) significantly reduced. In contrast, that of trypsin increased markedly due to denaturation of BSA by the tannins. Tannin concentrations in excess of 0.5% strongly inhibited the activation of chymotrypsinogen, while the activation of trypsinogen by enterokinase was drastically reduced at concentrations as low as 0.05% due to precipitation of the substrate. BSA digestion was markedly reduced in sequential multizymogen experiments at tannin concentrations of 0.5% but not at 0.1%.