Effect of Postharvest Application of Melatonin on reducing Chilling Injury in Cucumber (Cucumis sativus L. "Nagin")

Low temperature is an effective method to maintain product quality during the post-harvest period, but due to the sensitivity of cucumber fruits to chilling injury, the use of proper alternative techniques to chilling control are essential. In order to evaluate the use of melatonin to control chilling damage on cucumber, a factorial experiment based on a completely randomized design was conducted with three replications. The experimental factors included: different storage times (control = harvest day, 4, 8, and 12 days after harvest) and different concentrations of melatonin (0, 1, 10, and 100 μM). Some biochemical and physiological parameters including PAL activity, antioxidant enzymes (catalase, superoxide dismutase, ascorbate peroxidase and lipoxygenase) activities, malondialdehyde, phenolics and total protein content, electrolyte leakage, total soluble solids content and fruit firmness were measured. Melatonin in storage periods increased phenolic content and catalase and lipooxigenase activity. This increase was observed in all tested concentration of melatonin alongwith increasing the storage time up to 8 days but then reduced. Concerning SOD activity and total protein content, the increase was just until the fourth day and then decreased. Also, in all tested levels of melatonin, with storage time up to 12 days, malondyldehyde and electrolyte leakage showed an increasing trend, but fruit firmness had a decreasing pathern. TSS content decreased with time in all melatonin concentrations, which was more evident in untreated fruits. Moreover, in all tested concentration of melatonin, the activity of antioxidant enzymes and fruit firmness decreased by time up to 12 days. Overall, the results showed that melatonin treatment, especially at 100 μM, could diminish chilling injury and maintain the postharvest quality of cucumber fruits during cold storage.