Melatonin treatment mitigates chilling injury in cold-stored guava fruit by regulating the metabolisms of reactive oxygen species and membrane lipid

Melatonin enhanced chilling tolerance and reduced chilling injury in cold-stored guava. • Melatonin preserved cell membrane integrity in cold-stored guava. • Melatonin enhanced ROS-scavenging ability of cold-stored guava. • Melatonin reduced ROS accumulation and membrane lipid peroxidation in guava. • Melatonin lowered activities of membrane lipid-degrading enzymes in cold-stored guava. Guava fruit is highly susceptible to chilling injury during low-temperature storage. Melatonin acts as an effective approach to mitigate chilling injury in fresh produce during cold storage. In this work, the effects of 100 μmol/L melatonin treatment on chilling injury and the metabolisms of reactive oxygen species (ROS) and membrane lipid in guava fruit during storage at 4 ºC were explored. The results indicated that, compared to the control group, the melatonin-treated guavas exhibited the lower chilling injury incidence and cell membrane permeability, along with lower levels of O 2 -. , H 2 O 2 , and MDA. Additionally, the treated fruit showed the enhanced activities of SOD, POD, CAT, and APX, higher contents of AsA, lycopene, and GSH, and higher levels of DPPH radical scavenging ability, and reducing power. Furthermore, melatonin application lowered the activities of lipase, LOX, and PLD, resulting in higher levels of phosphatidylinositol, phosphatidylcholine, and USFAs, but lower levels of phosphatidic acid, and SFAs. Consequently, the indices of IUFA and U/S were also higher in the melatonin-treated guavas. Therefore, melatonin treatment mitigated chilling injury in cold-stored guavas through enhancing the ROS-scavenging system to reduce ROS generation and accumulation, as well as through inhibiting the activities of membrane lipid-degrading enzymes to maintain higher levels of phosphatidylinositol, phosphatidylcholine, and USFAs, thereby preserving the integrity of cell membrane.