Anthocyanins direct condensation between

Fig. 2.103. Structures of all the compounds found in fraction B (a) anthocyanins and acylated anthocyanins direct condensation products between flavanols and anthocyanins (c) dimers resulting from the condensation mediated by acetaldehyde between anthocyanins and flavanols. Reprinted with permission from C. Alcalde-Eon el al. [236].

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. 

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