Pyranoanthocyanin-flavanol

He, J., Santos-Buelga, C., Silva A.M.S., Mateus N., De Freitas, V. (2006a). Isolation and qualification of oligomeric pyranoanthocyanin-flavanol pigments from red wines by combination of column chromatographic techniques. /. Chromatog. A 1134, 215-225. 

Finally, reactions of flavonoid and nonflavonoid precursors are affected by other parameters like pH, temperature, presence of metal catalysts, etc. In particular, pH values determine the relative nucleophilic and electrophilic characters of both anthocyanins and flavanols. Studies performed in model solutions showed that acetaldehyde-mediated condensation is faster at pH 2.2 than at pH 4 and limited by the rate of aldehyde protonation. The formation of flavanol-anthocyanin adducts was also limited by the rate of proanthocyanidin cleavage, which was shown to take place at pH 3.2, but not at pH 3.8. Nucleophilic addition of anthocyanins was faster at pH 3.4 than at pH 1.7, but still took place at pH values much lower than those encountered in wine, as evidenced by the formation of anthocyanin-caffeoyltartaric acid adducts, methylmethine anthocyanin-flavanol adducts,and flavanol-anthocyanin adducts. The formation of pyranoanthocyanins requiring the flavylium cation was faster under more acidic conditions, as expected, but took place in the whole wine pH range. Thus, the availability of either the flavylium or the hemiketal form does not seem to limit any of the anthocyanin reactions. 

More complex structures consisting of both malvidin 3-glucoside and flavanol units connected by different types of linkages, including direct, ethyl and A-type bonds have been partially characterized by mass spectrometiy in model solutions (72). Additionally, some of these compounds also contain pyranoanthocyanin moiety. 

Previous studies regarding the composition and amount of several pyranomv3glc-flavanol compounds in 3-, 4-, and 6-year-old Port wines have shown that pyranoan-thocyanin-procyanidin dimers were more abundant than pyranoanthocyanin-catechin monomers (He et al, 2006b). No relationship between the concentration of these compounds and the wine age was ascribed and their contribution to the red wine color remains unclear. 

---