Abstract: In order to study the effects of treatment with different concentrations of exogenous melatonin (MT) on the quality and antioxidant activity of mulberry fruits, ‘Luyou 7’ mulberry fruits were sprayed postharvest with MT solution at concentrations of 0, 100, 200, and 300 μmol/L. Fruit quality and physiological indicators were measured at regular intervals during storage. Additionally, principal component analysis (PCA) and entropy-weighted TOPSIS were used to comprehensively evaluate the preservation effects. The expression of key anthocyanin synthesis-related genes and antioxidant enzyme genes was detected. The results showed that MT treatments at all concentrations reduced the decay incidence, delayed fruit softening and water loss of mulberry fruits, increased the contents of soluble solids, vitamin C, 1-deoxynojirimycin, and maintained the stability of titratable acidity. Exogenous MT upregulated the expression of key anthocyanin synthesis-related genes (MaPAL, Ma4CL-2, MaDFR, and MaANS), and consequently delayed the decrease in anthocyanin content and promoted the accumulation of total flavonoids and total phenols, thereby enhancing DPPH free radical scavenging activity. Moreover, exogenous MT increased the relative expression levels of antioxidant enzyme genes (MasodC, MaSOD-Mn, MaPOD1, and MaCAT1), thus enhancing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) and inhibiting the accumulation of malondialdehyde (MDA). Two principal components, namely “quality deterioration-antioxidant activity” and “antioxidant enzyme-sugar metabolism”, were extracted, altogether explaining 80.48% of the total variance. Collectively, PCA and the entropy-weighted TOPSIS comprehensive score showed that treatment with 200 μmol/L achieved the highest score, indicating the best preservation effect. In summary, treatment with an appropriate concentration of exogenous MT significantly delayed the postharvest senescence of mulberry fruits and maintained their sensory and nutritional quality, with the most pronounced effect observed at 200 μmol/L.

Key words: mulberry fruits; melatonin; postharvest; storage performance; comprehensive evaluation