Abstract: In this study, melatonin solutions at different concentrations (0.25, 0.50 and 0.75 mmol/L) were sprayed on fresh shiitake mushrooms (Lentinus edodes). By evaluating the hardness, browning degree, brightness and cap opening of the mushrooms, during the 42-day storage a melatonin concentration of 0.50 mmol/L was selected to further investigate its effect on reactive oxygen species (ROS) metabolism and changes in the ultrastructure of shiitake mushroom cells after 28 days of storage. The results showed that 0.50 mmol/L melatonin treatment significantly decreased the respiration intensity, superoxide anion generation rate and hydroxyl generation capacity compared with the untreated control group, reducing these by 44%, 39.1%, and 24.4% at the end of the 42-day storage period, respectively. The melatonin treatment also decreased the accumulation of malondialdehyde (MDA) and H2O2 in the mushroom cells and maintained lower levels of carbonylation proteins and a more complete cell membrane structure. In addition, the total phenol and ascorbic acid contents, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity in the treatment group were significantly higher than those in the control group. Ultrastructural observations showed that the morphology of the cell wall and mitochondria were maintained well after the treatment. In conclusion, melatonin treatment effectively maintained the quality of postharvest shiitake mushrooms by reducing the production rate of ROS metabolites and improving the antioxidant capacity to reduce oxidative damage caused by ROS to mushrooms, and the best effect was observed at 0.50 mmol/L.

Key words: Lentinus edodes; melatonin; quality; reactive oxygen species metabolism