Assay of o-Diphenol Oxidizing Activity in Japahese Pear Polyphenoloxidase by Difference Spectra Spectrophotometry

Abstract

A difference spectral method was employed for determining the o-diphenol oxidizing activities in Japanese pear polyphenoloxidase (EC 1. 10. 3. 1), using a principle that ascorbic acid (AsA) reducesquantitatively the o-quinone formed from o-diphenol by a polyphenoloxidase. A linear relationship was observed between the AsA oxidation, which was expressed asE₂₄₃, and the reaction time, within about 10min. The rate of the AsA oxidation was proportional to the amount of the emyme present. These results showed that the AsA oxidation rate can be adopted for determining o-diphenol oxidizing activities. The activities during fruit development of Japanese pear were measured by this method. The strong activities of o-diphenol oxidation were found in young fruits and these activities sharply dropped as the fruits developed.