Formation of Pigment Precursor (+)-1′′-Methylene-6′′-hydroxy-2H-furan-5′′-one-catechin Isomers from (+)-Catechin and a Degradation Product of Ascorbic Acid in a Model Wine System

The present study investigates the contribution of ascorbic acid to the formation of pigment precursors in model white wine systems containing (+)-catechin as the oxidizable phenolic substrate. The two main colorless products in these systems were structurally characterized as isomers of (+)-catechin substituted at either C6 or C8 on the A ring with a furan-type unit, namely, (+)-1′′-methylene-6′′-hydroxy-2H-furan-5′′-one-6-catechin and (+)-1′′-methylene-6′′-hydroxy-2H-furan-5′′-one-8-catechin. A known degradation product of ascorbic acid, l-xylosone, was separately prepared and, when reacted with (+)-catechin, generated the same (+)-furanone-catechin isomers as in model white wine systems. Incubation of these isomers in wine-like conditions yielded yellow xanthylium cation pigments. This study has shown that undesirable spoilage reactions (yellow coloration) can occur from a breakdown product of ascorbic acid−l-xylosone.