Oxidation of Chlorogenic Acid, Catechins, and 4-Methylcatechol in Model Solutions by Combinations of Pear (<i>Pyrus communis</i> Cv. Williams) Polyphenol Oxidase and Peroxidase:  A Possible Involvement of Peroxidase in Enzymatic Browning

Abstract

To clarify the role of pear peroxidase (POD) in enzymatic browning, oxidation of 4-methylcatechol, chlorogenic acid, and (−)-epicatechin catalyzed by purified polyphenol oxidase (PPO), purified POD, or combinations of the two enzymes was followed by HPLC. It was shown that pear POD had no oxidative (oxygen dependent) activity. However, in presence of PPO, POD enhanced the phenol degradation. Moreover, when PPO was entirely inhibited by NaCl after different oxidation times, addition of POD led to a further consumption of the phenolic compound. Two mechanisms have been proposed to explain this additional consumption. First, our results have demonstrated that, whatever the substrate used, PPO oxidation generated H 2 O 2, the amount of which varies with the phenolic structure. Second, quinonic forms are used by POD as peroxide substrate. These two mechanisms associated with the kinetic properties of pear PPO and POD are consistent with an effective involvement of pear POD in enzymatic browning. Keywords: Enzymatic browning; pear; peroxidase; polyphenol oxidase