Abstract: In this study, to investigate the effects of melatonin on pericarp browning in rambutan fruit, postharvest ‘Baoyan7’ rambutan fruit was immersed in melatonin solutions at varying concentrations for 15 min, air-dried, and then stored at 25 ℃ for 6 days. The results demonstrated that melatonin treatment at each concentration delayed browning and the decline in the chromaticity a* value of rambutan pericarp, with the most pronounced effect being observed at 0.125 mmol/L melatonin. Physiological and biochemical analyses showed that melatonin treatment at 0.125 mmol/L repressed the increase in relative conductivity (RC) and malondialdehyde (MDA) contents, while retarding the increase in lipoxygenase (LOX), lipase (LPS) and phospholipase D (PLD) activities in rambutan fruit during storage, thereby preserving the integrity of the cell membrane. In addition, treatment with 0.125 mmol/L melatonin increased the contents of nicotinamide adenine dinucleotide (NADH) and flavin dinucleotide (FADH2), enhanced the activities of energy metabolism-related enzymes including succinate dehydrogenase (SDH), cytochromic c oxidase (CCO), H+-ATPase and Ca2+-ATPase, and maintained high levels of adenosine triphosphate (ATP) and energy charge, thus improving cellular energy status. Moreover, this treatment enhanced γ-aminobutyric acid (GABA) content, and maintained high activities of glutamate decarboxylase (GAD) and GABA aminotransferase (GABA-T), thus contributing to enhanced cellular energy supply. These findings suggest that melatonin could retard postharvest browning and senescence in rambutan fruit by modulating membrane lipid and energy metabolisms.

Key words: rambutan; melatonin; browning; membrane lipid metabolism; energy metabolism