Exogenous melatonin as a natural preservative: a meta-analysis of its effects on fruit shelf life and oxidative stress during storage

Damage to fruits during the postharvest period is inevitable, with oxidative stress due to environmental factors being the primary cause. This meta-analysis aimed to investigate the consistent effects of exogenous melatonin application on postharvest fruit quality and shelf life by evaluating its influence on physiological parameters, antioxidant capacities, and oxidative stress-related factors. Meta-analysis via the Hedges' g random effects model was employed to assess 52 relevant studies, with model validation performed via Egger's test. The meta-analysis results indicated that exogenous melatonin application significantly reduced fruit damage parameters such as the browning index (g = - 0.542), fresh weight loss (g = - 0.689), and decay incidence (g = - 1.23; p < 0.001). Conversely, the values for chroma (g = 0.224), hue (g = 0.488), lightness (g = 0.154), and firmness (g = 0.444) increased significantly (p < 0.05). Chemical components such as ascorbic acid (g = 0.544), cellulose (g = 0.812), and titratable acidity (g = 0.308) also significantly increased (p < 0.001), while water-soluble pectin (g = - 0.935) decreased (p < 0.001). Antioxidant-related compounds, including phenolic acids, general flavonoids, and specifically pigmented molecules such as total anthocyanins (g = 0.33), increased significantly (p < 0.01), indicating enhanced fruit antioxidant capacity. Furthermore, exogenous melatonin led to an increase in the activity of antioxidant enzymes, such as ascorbate peroxidase (g = 0.751), catalase (g = 0.815), and glutathione reductase (g = 0.918; p < 0.001), while decreasing the activity of cell wall-degrading enzymes (p < 0.01). A positive trend was observed with a reduction in hydrogen peroxide (g = - 0.8) and malondialdehyde levels (g = - 0.696), both of which are related to oxidative stress. Moreover, application of exogenous melatonin at concentrations up to 500 <mu>M consistently tended to reduce decay incidence during storage for up to 60 days. On the basis of response surface methodology (RSM), the optimal dose is 116 mu M, which is predicted to result in a fresh weight loss of only 4.4% and an increase in ascorbic acid content to 57.3 mg/100 g of fresh weight. In conclusion, exogenous melatonin serves as an effective natural preservative that improves postharvest fruit shelf life by reducing the physiological activities associated with oxidative damage and enhancing antioxidant resistance.