Effect of Melatonin Treatment on Storage Quality and Antioxidant System of Postharvest Winter Jujube (Zizyphus jujube Mill. cv. Dongzao)

Low-temperature storage is an effective method to extend the shelf life of harvested winter jujube fruit; however, the quality of winter jujube fruit decreases after refrigeration. To enhance the quality of winter jujube with minimum qualitative deterioration during cold storage, this study investigated the effects of different melatonin concentration (100, 150, and 200 µmol/L) treatments on the storage quality of winter jujube (during the white ripening stage) at 0 ± 1 °C (RH, 90 ± 5%) for 90 days. The relative indexes of the fruit quality and the antioxidant system were measured every 15 days. The results showed that different concentrations of melatonin treatments could maintain the fruit's firmness, retard the fruit's redness, and inhibit the decrease in weight, total soluble solid (TSS), titratable acidity (TA), and the contents of total phenols, flavonoids, glutathione, and ascorbic acid; they also inhibited the increase in relative conductivity, malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) content of jujube fruits and enhanced antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and peroxidase (POD)). As a whole, the 200 µmol/L melatonin treatment had the best effect. Therefore, melatonin treatment can maintain the cold-stored quality of postharvest winter jujube by improving its antioxidant capacity.