Melatonin Activates Phenylpropanoid Metabolism and Antioxidant Defense to Preserve Quality of Fresh-Cut Potatoes During Cold Storage

To develop safe and effective preservatives for fresh-cut produce, this study elucidates the multi-pathway mechanisms through which Melatonin (MT) regulates postharvest senescence in fresh-cut potatoes. Treatment with 0.1 mmol/L exogenous MT effectively inhibited browning and softening during storage. In terms of browning control, MT suppressed PPO and POD activities by 46% and ~10% at the end of storage (day 12), while enhancing enzymatic and non-enzymatic antioxidant capacity by 1.1- to 1.6-fold on average throughout storage. This alleviated oxidative damage and membrane lipid peroxidation, thereby reducing tissue browning. Regarding texture maintenance, MT downregulated PME and cellulase activities by 23% and 19% at the end of storage, activated phenylpropanoid metabolism, and inhibited starch degradation (maintaining 19% higher starch content), thus preserving cell wall structure and firmness (9.2% higher at the end of storage). Further analysis revealed that MT antagonized ethylene biosynthesis, upregulated StMYB168 expression (5.8-fold higher than control on average), and activated endogenous MT biosynthesis, establishing a self-sustaining positive regulatory cycle. Correlation analysis confirmed close relationships among physiological processes, signaling responses, and quality traits, with significant associations between firmness and starch content (r = 0.72), color indices and PPO/POD (|r| > 0.65), and MT biosynthesis genes and metabolic pathways (r = 0.65–0.75) (p < 0.01).