Oxidation of Grape Juice Phenolic Compounds in Model Solutions

Abstract

ABSTRACT Oxidation of caftaric acid, catechin, epicatechin, epicatechin gallate, procyanidins B1 to B4 and 2‐S‐glutathionyl caftaric acid (GRP) in grape must‐like model solutions containing grape polyphenoloxidase was monitored by HPLC. Caftaric acid was degraded faster than catechin, epicatechin, and epicatechin gallate. Procyanidins and GRP were oxidized very slowly when incubated alone with the enzyme. Oxidation of two‐component mixtures in the presence of polyphenoloxidase was studied. Caftaric acid induced coupled oxidation of other compounds. The order of redox potentials was determined. Oxidation of catechin‐caftaric acid mixtures was studied, and the oxygen consumption measured. A reaction sequence including enzymatic oxidation, coupled oxidations and the formation of caftaric acid and catechin copolymers was proposed.