MECHANISMS OF ANTHOCYANIN DEGRADATION IN GRAPE MUST-LIKE MODEL SOLUTIONS

Oxidative degradation of o-diphenolic leg cyanidin-3-glucoside) and non-o-diphenolic leg malvidin-3-glucoside) anthocyanins in the presence of caffeoyltartaric acid and grape polyphenoloxidase was studied in model solutions. Both anthocyanins reacted with the enzymically generated caffeoyltartaric acid o-quinone. Kinetic studies indicated that cyanidin-3-glucoside was degraded mostly by coupled oxidation whereas malvidin-3-glucoside formed adducts with caffeoyltartaric acid quinone. In solutions containing equimolar amounts of the anthocyanins, both reactions took place but coupled oxidation of cyanidin-3-glucoside occurred at a faster rate, partly protecting malvidin-3-glucoside. The occurrence of coupled oxidation resulted in sparing of caffeoyltartaric acid. Several oxidation products, including red pigments, were detected by HPLC. The UV-Vis spectra of the coloured condensation products suggested that they contained both caffeoyltartaric acid and anthocyanin moieties. All these pigments were gradually degraded to colourless compounds either by enzymatic oxidation or by further reaction with quinones.