Abstract:

The harvested fruits of longan (Dimocarpus longana Lour.) are susceptible to pericarp browning, the most
important factor affecting the quality and shelf-life of harvested longan fruit. The difference in postharvest pericarp browning
between the longan cultivars ‘Dongbi’ (Dimocarpus longan Lour. cv. Dongbi) and ‘Fuyan’ (Dimocarpus longan Lour. cv.
Fuyan) during storage at (8 ± 1) ℃ and 85% relative humidity in relation to the metabolisms of active oxygen and phenolics
were investigated. The results showed that compared to ‘Fuyan’ longans, the browning index, superoxide anion (O₂^-·)
production rate, malondialdehyde content, and cellular membrane permeability were lower whereas the activities of active
oxygen scavenging enzymes, including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), were
significantly higher and the contents of endogenous antioxidant substances, like ascorbic acid (AsA) and glutathione (GSH),
were higher in the pericarp of ‘Dongbi’ longans during storage. In addition, lower activities of polyphenol oxidase (PPO) and
peroxidase (POD), and higher contents of anthocyanin, flavonoid and total phenolics in pericarp of ‘Dongbi’ longans during
storage were observed as compared to ‘Fuyan’ longans. From the above results, it could be concluded that ‘Dongbi’ longans
tend to be less susceptible to postharvest pericarp browning, which was due to higher active oxygen scavenging capacity,
resulting in reduced accumulation of O₂^-·, alleviated cellular membrane lipid peroxidation, maintained structural integrity of
the cellular membrane, and prevention of PPO and POD from contacting their phenolic substrates, and thus, reducing the
occurrence of enzymatic browning in the pericarp of ‘Dongbi’ fruit.

Key words: longan (Dimocarpus longana Lour.) fruit, pericarp browning, difference, cultivar, active oxygen metabolism, phenolics metabolism