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 oxidase (PPO) was studied in model solutions. The reactions were monitored by spectrophotometric, 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 pigment. 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 μmol of oxygen per μmol of CG oxidised, which is close to the stoichiometry calculated from the oxidation of CG alone (0.63 μmol of oxygen per μmol). The initial phase of the pigment degradation showed a delay which did not correspond to cresolase activity. This phase could be explained by a quinone/anthocyanin reaction which is dependent on the chlorogenoquinone concentration and/or a reaction involving secondary products of oxidation (formed from the chlorogenoquinone) and Pg 3-glc.