POLYPHENOL OXIDASE OF d'ANJOU PEARS (Pyrus communis L.)

Abstract

ABSTRACT Stability, substrate and inhibitor specificity and electrophoretic properties of a crude polyphenol oxidase (PPO) preparation extracted from d'Anjou pears (Pyrus communis L.) were investigated. The pH optimum of PPO occurs at 7.0. Heat inactivation of PPO followed first order kinetics and approximately 50% of PPO activity was inactivated after heating for 11.7, 6.25, 2.24 and 1.1 min at temperatures of 70°, 75°, 80° and 85°C, respectively. Crude PPO extract was active towards o ‐dihydroxyphenols, but inactive towards monophenols. Disc electrophoresis revealed eight active isozymes toward catechol, 4‐methyl catechol, chlorogenic acid, caffeic acid, dopamine, d‐catechin and DL‐dopa. Similar electrophoretic patterns were observed with all substrates. No differences in the electrophoretic patterns were observed between fresh PPO preparations and preparations which had been frozen or dialzyed. Pear PPO was relatively sensitive to most inhibitors tested with the exception of sodium chloride. Of the inhibitors studied L‐cysteine and diethyldithiocarbamate were the most effective against pear PPO.