Influence of procyanidin structures on their ability to complex with oenin

Intermolecular copigmentation between malvidin-3-O-glucoside (oenin) and several procyanidins of a homogeneous series in a wine model solution (pH 3.6, in hydroalcoholic (12%) citrate-phosphate buffer at a ionic strength of 0.2 M) was studied by UV-Vis spectroscopy. The effects of structural factors and stereochemistry of flavan-3-ol on their ability to interact with oenin were analysed. The presence of a galloyl group in the flavan-3-ol structures increased the strength of copigmentation. The strength of the interaction was not related to the degree of polymerisation for (−)-epicatechin, dimer B2 on trimer C1. Dimers with a C4-C6 interflavonoid linkage associated more strongly with oenin than did their C4-C8 analogues. Above all, the extent of copigmentation was influenced by the conformation of each procyanidin and its ability to establish a hydrogen-bonded network with the water medium.