The role of active oxygen metabolism in hydrogen peroxide-induced pericarp browning of harvested longan fruit

Effects of hydrogen peroxide (H2O2), as exogenous reactive oxygen, on browning and active oxygen metabolism in pericarp of harvested ‘Fuyan’ longan fruit were investigated. The results showed that as compared with the control fruit, there was a higher browning index in pericarp of H2O2-treated fruit. The fruit treated with H2O2 resulted in increased rate of superoxide anion (O2−) production, reduced activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), decreased amounts of ascorbic acid (AsA), glutathione (GSH) and carotenoid, and increased malondialdehyde (MDA) content. These results indicated that H2O2-induced browning in pericarp of harvested longan fruit might be due to a reducing capacity of active oxygen scavenging and an increase of accumulation of O2−, which might stimulate membrane lipid peroxidation, disrupt cellular membrane structure, and cause the loss of cellular compartmentalization, in turn, resulting in the contact of polyphenol oxidase (PPO) and peroxidase (POD) with phenolic substrates and subsequently oxidation phenolics to form brown polymers.