BROWNING OF LITCHI FRUIT PERICARP: ROLE OF POLYPHENOL OXIDASE, PEROXIDASE, PHENYLALANINE AMMONIA LYASE AND EFFECT OF GAMMA RADIATION*

ABSTRACT A dose of 0.5 kGy of gamma radiation in combination with low temperature storage (4C) helped in extending the shelf life of two Indian litchi (Litchi chinensis) cultivars ("Shahi" and "China") up to 28 days. However, during storage, pericarp browning in litchi was observed. Hence, in the current study to understand the mechanism of pericarp browning, total phenolics and the activities of polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL) were evaluated. The PPO activity and phenolics were found to be higher in "China" than in "Shahi," whereas POD and PAL activities were higher in "Shahi." PPO and phenolics played a major role in the pericarp browning. Radiation treatment increased the PAL activity and hence the level of total phenolics, whereas PPO and POD activities were inhibited. This may explain reduction in browning in irradiated fruits compared with nonirradiated fruits. PRACTICAL APPLICATIONS Browning of litchi pericarp affects the appeal of the fruit and is one of the main problems encountered by the cultivators and traders, leading to significant economic losses. Understanding the role of different enzymes and level of phenolics in the process of browning will help find suitable postharvest methods for the control of browning. As the radiation treatment is being used as a mandatory quarantine treatment in many countries for export, further understanding the effect of radiation treatment on the browning and related enzyme activities will help in postharvest management and improving international trade of litchi.