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.