Structure-reactivity relationship of monomeric flavan-3-ols in forming ethyl-linked anthocyanin pigments: an...

This study systematically investigated the reactivity of four major monomeric flavan-3-ols in wine, including (+)-catechin (C), (-)-epicatechin (EC), (+)-catechin-3-O-gallate (CG), and (-)-epicatechin-3-O-gallate (ECG), in forming ethyl-linked pigments with malvidin-3-O-glucoside in a model wine system. Kinetic analysis revealed a distinct reactivity order: C > ECG > EC > CG, indicating that both C2 stereochemistry and galloylation critically modulate the reaction rate. Quantum chemical calculations showed that the R-configuration in C favors a transition state with minimal steric hindrance, whereas galloylation exerts opposite effects depending on the core stereochemistry-introducing steric blockage in the C-series but promoting transition state stabilization in the EC-series through weak non-covalent interactions. Colorimetric evolution confirmed that ethyl-linked pigments formation significantly enhances color intensity. These findings provide molecular insights into the structure-reactivity relationships of monomeric flavan-3-ols and contribute to a deeper understanding of derived pigments formation and color evolution in red wine aging.