ABSTRACT
Catechin is a three-ring chemical structure characterized by a 15-carbon membered (C6-C3-C6 ¼ 6-carbon ring, 3-carbon ring, 6-carbon ring) flavan skeleton (Fig. 1), composed of a chromane nucleus (C6-C3) (rings A and C), also shared by the tocopherols, bonded to an aromatic ring (the B-ring) with hydroxyl group (–OH) substitutions. The substitution of –OH, at carbon-3 (Cring, Fig. 1) of the flavan confers it the name flavan3-ol, known by its trivial name catechin (Fig. 3). The condensation of two such flavan molecules by carboncarbon (–C-C-) linkage forms a 30-carbon containing unit, a dimer, the smallest member of the procyanidin class (Fig. 4). The treatment of a procyanidin (or generically, any proanthocyanidin)withmineral acid ruptures the carbon-carbon (–C-C-) linkage and generates cyanidin (an anthocyanidin), a brilliant, bright colored pigment associated with colored grape varieties, colored fruits, etc. Hence the name procyanidin (proanthocyanidin).
