Effect of Ethanol Treatment on Flesh Darkening and Polyphenoloxidase Activity in Japanese Persimmon, cv. 'Hiratanenashi'

Abstract

California, Davis, California 95616, U.S.A. Ethanol vapor treatment on the tree to intact fruit of Japanese persimmon cv. 'Hiratanenashi' removed its astringency quickly and induced flesh darkening within 3 weeks. Ethanol treatment did not promote the browning reaction of fruits stored at 1°C. The crude polyphenol oxidase (PPO) preparation obtained from the mesocarp as an acetone powder was much more active when extracted at 24° than when extracted at 5°C. of the 5 common substrate polyphenols tested, 4-methyl catechol was oxidized most rapidly by the enzyme. PPO activity increased sharply just after the loss of astringency coincidentally with the initial appearance of darkening in the calyx end. This high activity was maintained while the darkening was progressing throughout the entire flesh.