Polymeric proanthocyanidins are catabolized by human colonic microflora into low-molecular-weight phenolic acids

Polymeric proanthocyanidins are common constituents of many foods and bever ages. Their fate in the human body remains largely unknown. Their metabolis m by human colonic microflora incubated in vitro in anoxic conditions has b een investigated using nonlabeled and C-14-labeled purified proanthocyanidi n polymers. Polymers were almost totally degraded after 48 h of incubation. Phenylacetic, phenylpropionic and phenylvaleric acids, monohydroxylated ma inly in the meta or pam position, were identified as metabolites by gas chr omatography coupled to mass spectrometry (GC-MS). Yields were similar to th ose previously reported for flavonoid monomers. These results provide the f irst evidence of degradation of dietary phenolic polymers into low-molecula r-weight aromatic compounds. To understand the nutritional properties of pr oanthocyanidins, it is therefore essential to consider the biological prope rties of these metabolites.