Postharvest Melatonin Treatment Promotes Phenolic Compounds and Endogenous Melatonin Accumulation in Yellow-Flesh Peach ( Prunus persica L.)

BACKGROUND: The postharvest quality of yellow-flesh peach is compromised by rapid deterioration, necessitating effective preservation strategies. OBJECTIVE: This study investigated the efficacy of exogenous melatonin in enhancing the postharvest quality, phenolic compounds, and endogenous melatonin levels in yellow-flesh peaches. METHODS: Fruits were treated with 0.1 mM melatonin and stored for 28 days at 4°C and 90% relative humidity. Key quality parameters, phenolic profiles, gene expression, and enzyme activities were analyzed. RESULTS: Melatonin treatment significantly enhanced ascorbic acid content and elevated the levels of specific phenolic compounds, including gallic, chlorogenic, p-coumaric, and caffeic acids, as well as the flavonoids rutin and catechin. This biochemical improvement was underpinned by the upregulated expression of phenolic biosynthesis genes PpPAL, PpC4H, and Pp4CL. Concurrently, the treatment boosted the activities of key enzymes in the melatonin biosynthesis pathway, including tyrosine decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), and N-acetylserotonin methyltransferase (ASMT), leading to a significant accumulation of endogenous melatonin. CONCLUSION: Postharvest melatonin application is a promising technique for preserving quality and stimulating the biosynthesis of bioactive phenolic compounds and endogenous melatonin in yellow-flesh peaches. HIGHLIGHTS: Postharvest melatonin treatment improved peach fruit quality by elevating ascorbic acid and phenolic compounds, specifically enhancing four phenolic acids and two flavonoids. Mechanistic analysis revealed these improvements were driven by upregulated phenolic biosynthetic genes (PpPAL, PpC4H, Pp4CL) and concurrent activation of melatonin pathway enzymes (TDC, T5H, SNAT, ASMT), which collectively enhanced both phenolic and endogenous melatonin biosynthesis.