Melatonin treatment delays postharvest senescence of ‘Dayagan’ hybrid citrus fruit by enhancing reactive oxygen species-scavenging capacity and preserving higher unsaturated fatty acid content

This study sought to investigate whether melatonin (MT)-induced alterations in membrane fatty acid and reactive oxygen species (ROS) metabolism are associated with senescence of citrus fruits during storage. The findings demonstrated that applying 1 g L⁻¹ MT reduced the respiration rate, delayed weight loss and decay, and maintained better inner fruit quality. MT alleviated oxidative damage and protected membrane stability by lowering malondialdehyde and electrolyte leakage levels. MT increased the antioxidant content (ascorbic acid, total phenols, and total flavonoids) along with enhancing the ferric ion-reducing antioxidant power and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and promoted the activity of enzymes like superoxide dismutase, peroxidase, and catalase, thereby decreasing ROS accumulation. MT-treated fruits had higher unsaturated fatty acid (USFA) content by regulating lipase and lipoxygenase, which contributed to improving the ratio of USFAs to saturated fatty acids and the double-bond index. Furthermore, a significant relationship between membrane stability and postharvest fruit senescence was confirmed. These results suggest that MT inhibits postharvest physiological senescence and enhances the storage performance of citrus fruits by enhancing ROS-scavenging capacity and preserving higher unsaturated fatty acid content to alleviate membrane oxidative damage and maintain membrane stability.