KINETICS AND MECHANISM OF QUERCETIN OXIDATION

Abstract

The kinetics of quercetin oxidation in air were determined spectrophotometrically in the pH region 4 to 7 in 50% alcohol solution at 50° C. The rate at constant pH, found to be first order with respect to quercetin, exhibited pH dependence, with the rate rising with decreasing hydrogen ion concentration. Decrease in oxygen concentration was found to decelerate the reaction. Experiments using diphenyl picrylhydrazyl indicated the presence of free radicals. The mechanism of quercetin oxidation could be fitted into the model consistent with initial ionization of quercetin to its anion and its subsequent reaction with oxygen in a fast step, followed by a unimolecular decomposition to the oxidized quercetin and hydroxyl ion via a one electron transfer mechanism. The primary step in the formation of chill haze in beer appears to be the oxidation of the phenolic entity. 1972 The Institute of Brewing & Distilling