EFFECT OF HIGH-TEMPERATURE CONDITIONING ON ETHYLENE, PHENYLALANINE AMMONIA-LYASE, PEROXIDASE AND POLYPHENOL OXIDASE ACTIVITIES IN FLAVEDO OF CHILLED FORTUNE MANDARIN FRUIT

The susceptibility of (Fortune, citrus fruit to chilling injury (CI) w as markedly decreased by conditioning the fruit for 3 days at 37 degre es C. Rate of ethylene formation and changes in the activities of the phenolic enzymes, phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenol oxidase (PPO), were measured in conditioned and non-con ditioned mandarins during temperature storage. No correlation was foun d between the development of chilling symptoms in non-conditioned frui t and the changes in PPO and POD activities in the flavedo. The POD ac tivity was higher in high temperature conditioned mandarins than in no n-conditioned mandarins throughout the storage period. The increase in peel damage was concomitant with an increase in PAZ, activity, which followed that in ethylene production. These responses of 'Fortune' fru it to chilling were overriden by the heat treatment given before chill ing exposure. Our data suggest that the reduction in CI induced by hea t conditioning may involve changes in ethylene production, and PAL and POD activities.