A novel method for proanthocyanidin polymerization profiling reveals the synergistic effects of concentration and composition on red wine astringency and salivary protein binding

Proanthocyanidins (PAs) are key contributors to wine astringency, yet their structure complexity and low concentrations hinder accurate analysis. In this study, a solid-phase extraction method was optimized and validated for quantifying PAs with degrees of polymerization (DP) 1–8 in commercial red wines. Both PA concentration and DP distribution distinguished wines with different astringency intensities, with PA proportions across DP contributing more strongly to classification model than corresponding concentrations. Artificial Saliva Precipitation Index (ASPI) analysis in model wine systems further confirmed that total PA concentration alone is not a reliable predictor of astringency, emphasizing the synergistic influence of PA concentration and proportion on perceived intensity. Moreover, salivary protein reactivity followed a defined sequence—proline-rich proteins (PRPs), lactoferrin, lysozyme, BSA, and amylase—with amylase exhibiting the lowest affinity for PAs across DP. Protein affinity for PAs was governed primarily by the accessibility of the peptide backbone (open random-coil vs. compact globular conformation) and the distribution of hydrophobic and proline-rich surface patches, rather than by molecular weight or abundance. These findings provide new mechanistic insights into wine astringency perception.