Abstract:

Cucumber is a kind of vegetable with short storage time（2–3 days）at ambient temperature. The objective of this study was to optimize postharvest melatonin handling conditions to reduce the quality loss and extend the shelf life of cucumber. The cucumbers were dipped in 0，50，100 or 500 μmol ? L-1 melatonin solution immediately after harvest. Changes in quality index，chlorophyll concentration，vitamin C，tissue electrolyte leakage，MDA content，active oxygen content and activity of antioxidant enzymes were monitored periodically during storage at 10 ℃ for15 days. Results indicated that exogenous melatonin treatment slowed down the decrease of chlorophyll，vitamin C，and the content of titration-acid and soluble protein of postharvest cucumber during storage. The further study showed exogenous melatonin treatment reduced the fruit relative conductivity，MDA content，active oxygen content and activity of antioxidant enzymes（SOD，CAT，POD，APX），and also inhibited the respiration intensity and the ethylene production，reduced the oxidative damage to cells and maintained a more complete cell structure. 100 μmol ? L-1 melatonin solution dip showed the highest overall quality，lowest tissue electrolyte leakage，MDA content，and maximum reduction of oxidative damage on the cells.

Key words: cucumber, postharvest, melatonin, quality, shelf-life