The Fate of Anthocyanins in Wine: Are There Determining Factors?

Abstract

After extraction, grape anthocyanins undergo many reactions during winemaking and ageing. Relative amounts of anthocyanins and tannins, dissolved oxygen, pH, and presence of yeast metabolites (e.g. acetaldehyde, pyruvic acid) influence these reactions. pH controls reactivity because at low pH the electrophilic flavylium ion is the most abundant form of anthocyanin whereas at higher pH the nucleophilic hydrated is the most abundant form. Tannin to anthocyanin ratio determines the proportions of tannin derivatives, tannin anthocyanin adducts and anthocyanin polymers. Wine exposure to oxygen favors ethanol oxidation to acetaldehyde and susbsequent reactions involving acetaldehyde. Acetaldehyde-induced reactions first lead to ethyl-linked species, including flavanol oligomers, anthocyanin oligomers and tannin-anthocyanin adducts. Acid catalysed cleavage of the labile ethyl-bonds between flavanol units followed by addition of the resulting species onto flavylium ions then generates pyroanoanthocyanins. Current knowledge on the impact of wine-making processes on formation of anthocyanin-derived pigments as well as their impact on wine organoleptic properties is discussed.