F-A+ pigments

F-A pigments are described to result from the direct condensation between anthocyanins and condensed tannins (proanthocyanidins). The presence of these pigments in wines was confirmed recently (Salas et al, 2004a). Their formation mechanism was described to involve two fundamental steps (see Fig. 3.9) first, the acid-catalyzed cleavage of inter-flavan linkage of proanthocyanidins, yielding a carbocation in C-4 and then, the carboca-tion may react on the nucleophilic position C-8, or less likely the C-6, of the hemiacetal form of anthocyanin to form the F-A adduct. 

The F-A+ pigments formation is expected to occur very slowly during wine aging because the acid-catalyzed cleavage of the intervanoid linkage of proanthocyanidins is not straightforward at wine pH. Recently, Salas et al (2003) have demonstrated that the... 

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