Colonic metabolites of berry polyphenols: The missing link to biological activity?

Abstract

The absorption of dietary phenols, polyphenols and tannins (PPT) is an essential step for biological activity and effects on health. Although a proportion of these dietary bioactive compounds areabsorbed intact, depending on their chemical structure and the nature of any attached moiety (e.g. sugar, organic acid), substantial amounts of lower molecular weight catabolites are absorbedafterbiotransformation by the colon microflora. The main products in the colon are (a) benzoic acids (C6-C1), especially benzoic acid and protocatechuic acid; (b) phenylaceticacids(C6-C 2), especially phenylacetic acid per se; (c) phenylpropionic acids (C6-C3), where the latter are almost entirely in the dihydro form, notablydihydrocaffeicacid, dihydroferulic acid, phenylpropionic acid and 3-(3́-hydroxyphenyl)-propionic acid. As a result of this biotransformation, some of these compounds can each reach mmconcentrations in faecalwater. Many of these catabolites are efficiently absorbed in the colon, appear in the blood and are ultimately excreted in the urine. In the case of certain polyphenols, such asanthocyanins, these catabolites are major products in vivo; protocatechuic acid is reported to represent a substantial amount of the ingested dose of cyanidin-3-O-glucoside. The major catabolites of berries, and especially blackcurrants, arepredicted based on compositional data for polyphenols from berries and other sources. Since microbial catabolites may be present at many sites of the body in higherconcentration than the parent compound,it is proposed that at least a part of the biological activities ascribed to berry polyphenols and other PPT are due to their colonic catabolites. © The Authors 2010.