Low-Concentration Exogenous Sodium Hydrosulfide Enhances Antioxidant Defense and Delays Quality Deterioration in Ambient-Stored Tribute Citrus ( Citrus reticulata )

To elucidate the mechanism underlying the hydrogen sulfide (H₂S)-mediated delay of quality deterioration in stored tribute citrus, fruits were treated with exogenous NaHS and the physiological and biochemical changes were assessed. Over a 16-day storage period, fruits were analyzed every 4 days, and various parameters were measured in triplicate, including colorimetry, chlorophyll, and key biochemical components. High NaHS concentrations (5–30 μmol/L) accelerated senescence, whereas 0.5 μmol/L NaHS exerted significant preservative effects, markedly inhibiting color change (ΔH* = 12.3%), chlorophyll degradation (38.7%), and soluble protein loss (p < 0.01) in the peel. This treatment also maintained soluble solid content (p < 0.05) and delayed the decrease in vitamin C (p < 0.01) and soluble sugar (p < 0.01) in the pulp, thereby preserving overall nutritional quality. Concurrently, POD and CAT activities were upregulated by a maximum of 1.4- and 1.8-fold, respectively, during storage (on day 8). In summary, 0.5 μmol/L NaHS treatment effectively retards ripening and senescence, offering realistic prospects for the development of eco-friendly preservation technologies.