Monomeric flavan-3-ols are important copigments in red wines, due to their superior copigmentation ability and high concentration. In this work, a systematic study was conducted on the copigmentation effects of eight common monomeric flavan-3-ols with malvidin-3-O-glucoside, using experimental and theoretical methods. The results revealed that the addition of a hydroxy group to the B ring and the attachment of a galloyl group at the 3-O position of monomeric flavan-3-ols both contributed to enhance copigmentation, with the latter exerting a more pronounced effect. Regarding stereoisomerism, it was observed that the cis-configuration of the B ring and 3-O-hydroxy group favored copigmentation. However, the cis-configuration of the B ring and 3-O-galloyl group was disadvantageous due to steric hindrance, in contrast to when these moieties occupied opposing sides (i.e., the 2,3-trans configuration). These results highlight the crucial role played by both substitution patterns and conformational arrangements in determining the copigmentation ability of monomeric flavan-3-ols.
Keywords: Flavan-3-ols; IGMH analysis; Intermolecular copigmentation; Stereoisomers; Thermodynamics.
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