Degradation of pelargonidin 3-glucoside in the presence of chlorogenic acid and blueberry polyphenol oxidase

Oxidation of both chlorogenic acid (CG) and pelargonidin 3-glucoside (Pg 3- glc) as well as their mixture, in the presence of blueberry polyphenol oxid ase (PPO) was studied in model solutions. The reactions were monitored by s pectrophotometric, polarographic and HPLC methods. In the absence of CG, Pg 3-glc is not oxidised by blueberry PPO, but pigment degradation is induced by the presence of chlorogenic acid. Kinetic studies showed that Pg 3-glc was degraded by a mechanism involving a reaction between chlorogenoquinone and/or secondary products of oxidation formed from the quinone and the pigm ent. Therefore, no coupled oxidation mechanisms occurred with Pg 3-glc, as expected of its structure. The oxidation of CG by PPO in the presence of Pg 3-glc involved the consumption of 0.6 mu mol of oxygen per mu mol of CG ox idised, which is close to the stoichiometry calculated from the oxidation o f CG alone (0.63 mu mol of oxygen per mu mol). The initial phase of the pig ment degradation showed a delay which did not correspond to cresolase activ ity. This phase could be explained by a quinone/anthocyanin reaction which is dependent on the chlorogenoquinone concentration and/or a reaction invol ving secondary products of oxidation (formed from the chlorogenoquinone) an d Pg 3-glc. (C) 1999 Society of Chemical Industry.