Proanthocyanidins and tannin-like compounds - nature, occurrence, dietary intake and effects on nutrition and health

Proanthocyanidins (syn condensed tannins) are complex flavonoid polymers na turally present in cereals, legume seeds and particularly abundant in some fruits and fruit juices. They share some common structural features-phenoli c nature and high molecular weight-with phenolic polymers found in black te a and red wine (called here tannin-like compounds). The polymeric nature of proanthocyanidins makes their analysis and estimation in food difficult. F or this reason, little is known about their consumption, although they like ly contribute a large part of the daily polyphenol intake. They also share common physicochemical properties: they form stable complexes with metal io ns and with proteins and are, like other polyphenols, good reducing agents. Many of their biological effects of nutritional interest derive from these properties. As metal ion chelators, they influence the bioavailability of several minerals. The nutritional significance of the non-specific complexa tion of proteins is less clear. As reducing agents, they may participate in the prevention of cancers, both of the digestive tract, and inner organs. They may also protect LDLs against oxidation and inhibit platelet aggregati on and therefore prevent cardiovascular diseases. In vitro, animal and huma n studies on the prevention of these chronic diseases are reviewed with par ticular attention to wine and tea polyphenols. The lack of data on their bi oavailability and the paucity of human studies are emphasised. (C) 2000 Soc iety of Chemical Industry.