Copigmentation of procyanidin dimers with malvidin-3-O-glucoside: Impacts on color and stability in model wine

This study investigated the impacts of procyanidins B1 and B2, the predominant dimeric proanthocyanidins in red wine, on anthocyanin color and stability. A combination of spectrophotometry, thermodynamic analysis, time-dependent density functional theory calculations, and UHPLC-Q-TOF-MS was used. It was demonstrated that procyanidins B1 and B2 exhibit weak and comparable copigmentation abilities (K = 55.89 and 51.56 L mol^-1, respectively), significantly lower than monomeric flavan-3-ols. Their non-planar conformations impede optimal π-π stacking with malvidin-3-O-glucoside, resulting in minimal bathochromic shifts (up to 3 nm) and hyperchromic effects (up to 30 % at a 1:40 M ratio). Simulated aging experiments further revealed that neither dimer affected anthocyanin stability during storage. However, both procyanidin dimers induced yellow hues likely through oxidation, with procyanidin B2 exhibiting greater oxidative instability and a more pronounced yellowing effect than B1. These findings indicate that while procyanidins B1 and B2 are unlikely to directly alter anthocyanin color expression through copigmentation and may have minimal impact on anthocyanin stability, their self-oxidation represents a significant pathway for color evolution towards yellow hues.