Chapter 2: Occurrence, Bioavailability and Metabolism of Berry (Poly)phenols

Berries are a rich dietary source of (poly)phenols, including anthocyanins, flavan-3-ols, flavonols, ellagitannins and phenolic acids. In populations with low consumption of berries, their contribution to the overall ingestion of (poly)phenols can, nonetheless, be high in comparison to other food sources. For many years, (poly)phenols were considered to be poorly bioavailable in humans, with the limited appearance of their phase II metabolites in the circulatory system occurring post-absorption in the proximal gastrointestinal tract. Nowadays, there is a growing realization that berry (poly)phenols are highly bioavailable as a consequence of them passing from the small to the large intestine, where, as a result of the action of the resident microbiota, they are degraded to phenolic catabolites, which are absorbed into the bloodstream in substantial amounts. As a result of different degradation steps, class-specific colonic catabolites, such as phenyl-γ-valerolactones and urolithins, can form. Other catabolites, namely phenylpropanoic acids, phenylacetic acids, benzoic acids and phenol derivatives, are common breakdown products of almost all (poly)phenolic classes. The complexity of the composition of the colonic microflora has been associated with inter-individual variability and the classification of subjects as non-, low- and high-producers of phenolic catabolites.