ANTHOCYANIN DEGRADATION IN OXIDIZING GRAPE MUSTS

White musts with added grape anthocyanis were prepared and oxidised using known amounts of oxygen. Although malvidin and peonidin glucosides were degraded at a slower rate than o-diphenolic anthocyanins, important losses of all pigments occurred in oxidising grape musts. Degradation was inhibited by glutathione in excess, meaning that enzymically generated quinones of caffeoyltartaric acid were involved in the degradation mechanisms. Addition of anthocyanins hardly modified the kinetics of caffeoyltartaric acid oxidation and conversion to 2-S-glutathionyl caffeoyltartaric acid (grape reaction product). All musts browned considerably during oxidation. Browning of white musts was measured as an increase of redness (a*) and a decrease of lightness (L*) and yellowness (b* and hue angle) whereas browning in anthocyanin added musts appeared essentially as a loss of red colour (a*).