Relation between Polyphenol Oxidase and Postharvest Pericarp Browning in Different Litchi Cultivars

The relationship between pericarp browning and polyphenol oxidase(PPO) activity among postharvest fruits of ‘ Feizixiao’,‘ Ziniangxi’ and ‘ Wuhe’,with different storability,were investigated in this paper.The results indicated that ‘Ziniangxi’ was the strongest storability cultivar and ‘Feizixiao’ followed.During postharvest storage,PPO activity increased firstly and then decreased in pericarp of ‘ Feizixiao’ and ‘ Ziniangxi’ no matter which treatment conducted,while adverse trend at low temperature in pericarp of ‘Wuhe’,of which PPO activity showed a decreasing trend at room temperature.During the early stage of postharvest storage,‘ Wuhe’ and ‘Ziniangxi’ showed the highest and lowest PPO activity of free form,bound form and total enzyme,respectively.On the first day of postharvest fruits,there were four,three and two PPO bands of isoenzymes in pericarp of ‘ Wuhe’,‘ Feizixiao’ and ‘ Ziniangxi’,respectively.No effect was found on different treatments and numbers of isoenzymes in pericarp of ‘ Feizixiao’ and ‘ Ziniangxi’,however,the numbers of PPO isoenzyme declined in pericarp of ‘Wuhe’ at low temperature.The results suggested that PPO and numbers of isoenzyme may contribute to the difference of postharvest browning process at early storage stage in pericarp.