The inhibition of digestive enzymes by polyphenolic compounds.

The ability of polyphenolic compounds to form insoluble complexes with other macro-molecules such as proteins has long been associated with the observed reduction in nutritive value resulting from their inclusion in animal diets. Naturally occurring polyphenols, and in particular condensed tannins isolated from various plant sources, have been shown to inhibit in vitro a number of digestive enzymes including trypsin, alpha-amylase and lipase. In addition, the results of various feeding trials suggest that similar reductions in intestinal digestive enzyme activity may result from the feeding of high polyphenolic diets. The evidence for this is summarised and discussed in relation to the possible effect of enzyme inhibition on reduced nutritive value and it is concluded that the observed reduction in protein availability found in vivo on consuming high tannin diets cannot simply be explained by the formation of dietary protein tannin complexes and that the ability of polyphenolic compounds to inhibit digestive enzymes may be of greater significance than realised previously.