Network and Multivariate Evidence for Synergistic Roles of Melatonin and Chitosan in Maintaining Postharvest Quality of Purple Passion Fruit

This study evaluated the combined effects of melatonin (Me) and chitosan (Chi) on postharvest physiology, antioxidant dynamics, and quality of purple passion fruit. Fruits were treated with Me (0, 0.1, 0.2 mM) and Chi (0, 1, 2%), alone or in combination, and stored at 25°C and 90% RH for 11 days. Nine physiological and biochemical indicators were measured at 1–11 days after treatment (DAT). Membrane integrity, assessed by electrolyte leakage (EL) and malondialdehyde (MDA), deteriorated progressively in controls. Treatments consistently suppressed EL, though MDA responses were less uniform and sometimes comparable to or higher than controls, suggesting partial rather than absolute suppression of lipid peroxidation. Non‐enzymatic antioxidants showed distinct patterns: vitamin C (VC) was stable in controls but significantly enhanced in treated fruits, especially under high‐dose combinations; ABTS antioxidant activity increased during early storage and was better maintained by treatments, largely driven by melatonin; total polyphenol content (TPC) increased steadily in all fruits, but declined in combined treatments at 11 DAT, reflecting reduced stress‐induced accumulation. Quality traits, titratable acidity (TA), and total soluble solids (TSS) were consistently better preserved under treatments, particularly Me0.2 + Ch2. Correlation and PCA analyses revealed that VC, TA, and TSS formed a central “quality–antioxidant hub” under treatments, while controls clustered with stress markers (MDA, EL, POD, TPC). Collectively, these findings highlight that Me and Chi act synergistically not simply by elevating antioxidants, but by restructuring antioxidant–quality networks, with Me0.2 + Ch2 emerging as the most effective, eco‐friendly strategy for prolonging passion fruit storability.