In accordance to the concentration of TP, the concentration of MA, at the beginning of the storage period, is slightly higher for variety Merlot. During storage for 11 months, an almost tenfold decrease in MA concentration was observed for both varieties.Color and taste changes taking place during wine aging have long been ascribed to conversion of grape anthocyanins to polymeric pigments through addition reactions with flavanols, i.e., catechinoligomers. Three mechanisms have been postulated: The first one involves nucleophilic addition of flavanols (in C8 or C6) onto the C4 position of the anthocyanin flavylium ion yielding 4-flavanylanthocyanins,
which are also referred to as anthocyanin–flavanol (A–F) or anthocyanin–tannin (A–T) adducts. The second mechanism is based on nucleophilic addition onto the carbonium ion formed in acid solutions from flavan 3,4-diols or by cleavage of procyanidins. Anthocyanins, either in the flavene form or in the hemiketal form, are added onto the carbonium ion, leading to F–A adducts. The third mechanism proposed, involves nucleophilic addition of the flavanol onto protonated acetaldehyde, followed by protonation and dehydration of the resulting adduct and nucleophilic
addition of a second flavonoid onto the carbocation thus formed. The resulting products are anthocyanin–flavonol adducts in which the flavonoid units are linked in C6 or C8 position through a methylmethine bond. These phenomena result in reducing the fraction of monomeric anthocyanins in wine (Cheynier, 2006;Figueiredo-González, Cancho-Grande, & Simal-Gándara, 2013;
Figueiredo-González et al., 2014). In a previous experimental work