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

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Abstract
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%.