Inhibitory effects of propyl gallate on browning and its relationship to active oxygen metabolism in pericarp of harvested longan fruit

The inhibitory effects of propyl gallate, an active oxygen scavenger, on browning and active oxygen metabolism in the pericarp of harvested ‘Fuyan’ longan fruit were investigated. The results indicated a lower browning index in the pericarp of propyl gallate-treated fruit when compared with the control fruit. The fruit treated with propyl gallate displayed a decreased rate of superoxide anion (O2·¯) production, maintained higher activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), had higher contents of ascorbic acid (AsA), glutathione (GSH) and carotenoid, and had lower malondialdehyde (MDA) content. These results give convincing evidence that the retardation of pericarp browning of harvested longan fruit is due to an increased capacity to scavenge active oxygen species and decrease the accumulation of O2·¯. Controlling the level of active oxygen species will reduce membrane lipid peroxidation, maintain cellular membrane structure and the integrity of compartmentalization. Preventing polyphenol oxidase (PPO) and peroxidase (POD) from contacting their respective phenolic substrate will reduce the occurrence of enzymatic browning in the pericarp of harvested longan fruit. It is possible that propyl gallate treatment could be a feasible technique for controlling pericarp browning and extend the storage life of harvested longan fruit.