Postharvest Melatonin Applications in Soft Fruits: Mechanisms and Factors Determining Treatment Efficacy

Abstract

Soft fruits are highly perishable due to their delicate surface barriers, rapid cell-wall disassembly, turgor loss, oxidative imbalance, and tightly coordinated ripening and senescence processes that collectively accelerate water loss, softening, and decay after harvest. This review examines how melatonin (MLT) interacts with these deterioration processes in blueberries, raspberries, strawberries, grapes, and sweet cherries. Current evidence identifies redox regulation as the most consistent mechanism of MLT action, including modulation of reactive oxygen species, enhancement of antioxidant enzymes and the ascorbate–glutathione cycle, and maintenance of phenolic and other non-enzymatic antioxidants. These responses are linked with lower lipid peroxidation, reduced membrane leakage, delayed cell-wall degradation, and improved firmness, water retention, and decay resistance. More limited and species-specific evidence suggests that MLT may influence cuticular wax metabolism, endogenous MLT biosynthesis, H2S signaling, GABA and polyamine metabolism, phenylpropanoid pathways, and host-defense responses. However, direct evidence for effects on cuticular permeability, cellular compartmentation, and hormonal signaling remains limited. Overall, MLT should be regarded as a context-dependent regulator of redox homeostasis, tissue integrity, ripening, and defense rather than as a universal anti-senescence treatment, because its effects vary with species, cultivar, concentration, maturity stage, and storage conditions and still require validation under commercial conditions.