Flavanol dimer, reactions with

Similarly, direct reactions between anthocyanins and a flavanol dimer (namely epicatechin-epicatechin 3-gallate) were investigated in model solutions at pH 2 and pH 3.8 (31). Compounds with mass values corresponding to epicatechin-anthocyanin adducts and to anthocyanin-epicatechin-epicatechin 3-gallate, were detected at pH 2 and pH 3.8, respectively. Given the structure of the flavanol precursor, the former can be interpreted as F-A+ arising from cleavage of the flavanol dimer followed by addition of the anthocyanin AOH form onto the epicatechin carbocation whereas the latter is presumably an A+-F species formed by nucleophilic addition of the flavanol dimer onto the flavylium cation. Anthocyanin dimers (A+-AOH) were detected in model solutions at pH... 

The formation of xanthylium pigments may also result from non enzymatic reactions of colorless precursors such as flavanols as previously reported (/yellow derivatives by various oxidation processes. In the presence of tartaric acid and iron or copper ions, yellow pigments with absorption maxima at 440 and 460 nm were formed along with the colorless (+)-catechin carboxymethine bridged dimers 46, 47). These pigments were analysed by ID and 2D NMR and identified as non esterified and esterified xanthylium salts respectively 33, 38, 39, 42) (Figure 5). 

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