Melatonin alleviated chilling injury of cold-stored passion fruit by modulating cell membrane structure via acting on antioxidant ability and membrane lipid metabolism.

Fresh passion fruit is sensitive to chilling injury (CI) during storage at improper low temperature of 5 °C, which lowers the fruit quality and limits its shelf life. The present study aimed to determine the impacts of melatonin on CI development of passion fruit in relation to antioxidant ability and membrane lipid metabolism during refrigeration. In present study, passion fruit was treated with 0.50 mmol L^-1 melatonin and distilled water (control) for 20 min, hereafter stockpiled at 5 °C. The results indicated that, in storage, melatonin-treated passion fruit showed the lower CI index and cell membrane permeability, lower superoxide anion production rate and malondialdehyde level, greater activities of catalase, superoxide dismutase and ascorbate peroxidase, higher levels of ascorbic acid and glutathione, and higher 1, 1-diphenyl-2-picrylhydrazyl radical scavenging capacity than control passion fruit. Besides, lower membrane lipid-degrading enzyme activities, lower contents of phosphatidic acid and saturated fatty acids (SFAs), higher levels of phosphatidylcholine, phosphatidylinositol and unsaturated fatty acids (USFAs), and greater ratio of USFAs to SFAs and index of USFAs were revealed in melatonin-treated passions than control passions. Thus, these results indicated that melatonin retained cell membrane structure via boosting antioxidant capacity and restricting membrane lipid degradation, accordingly increased the chilling resistance and delayed the CI development in fresh passion fruit.