Absorption and metabolism of proanthocyanidins

Proanthocyanidins are found in fruits, tree nuts, cereals, legumes, wine, and chocolate. They affect nutritional value, appearance, taste, and texture of these foods and promote better health by preventing cardiovascular diseases, cancers, urinary tract infections, and other aging-related metabolic complications. The bioavailability of proanthocyanidins is largely influenced by their degree of polymerization. The absorption rate of proanthocyanidin dimers is 5-10% of that of (−)-epicatechin. Trimers and tetramers had lower absorption rates than dimers. Absorbed intact dimers, trimers, and tetramers undergo limited phase II metabolism in the intestine and liver in rats compared with (−)-epicatechin. Proanthocyanidins with a degree of polymerization over 4 (DP > 4) are not absorbable because of their large molecular size and gut barrier. Depolymerization of proanthocyanidins in the gastrointestinal tract was negligible. The majority of proanthocyanidins reaches the colon intact and is degraded into phenylvalerolactones and phenolic acids by colon microbiota. These microbial metabolites may contribute to the health promoting properties of proanthocyanidins in vivo. Future research of proanthocyanidin bioavailability will likely focus on identification of new microbial metabolites and investigation of how proanthocyanidins influence human health by affecting the composition of human gut microbiota.