Manifolds of Melatonin Application with a Chitosan–CarboxyMethyl Cellulose Biocoating for Postharvest Ripening in Pepper Fruit: Cell Wall Degradation, Membrane Integrity, and DNA Damage

Melatonin (MT) is well known in plants for its antioxidative and promotive residues, sensitizing growth and developmental processes. For postharvest preservation of fruits, natural biodegradable coating materials have been used in combination with different growth-substitutive substances. In brief, exogenous MT application following coating in chitosan–carboxymethyl cellulose (CHT–CMC) demonstrated its effects on the shelf life extension of pepper fruit. The aim of the work is also to present a CHT–CMC biocoating to extract the roles of MT in the minimization of oxidative stress, controlling ripening through storage. The concentration of MT at 100 μM was most effective with a coating of CHT–CMC in a 1:2 proportion on 7 days (D) for postharvest storage to delay the ripening. The recovery of fruit firmness (34%), loss of respiratory CO2 (45%), titrable acidity (48%), and fruit decay (75%) were significant compared to the 7-D control group. Reduction of cell wall hydrolysis was recorded through downregulation of endoglucanase (51%) and polygalacturonase (92%) gene expression against 7-D control under optimum MT concentration, which correlated with lipid peroxidation of the membrane. The viability of the fruit tissue was restored with the regulation of reactive oxygen species (ROS) and DNA loss in the optimized concentrations of MT. Greenness of fruit coat under storage was sustained by photochemical activities, malate decarboxylating reaction, alteration of sugar–acid conversion, and carbohydrate profiles. MT showed a higher efficiency in redox stabilization of the fruit, with significant upregulation of antioxidative enzymes and an improved ratio of ascorbate and glutathione. Conclusively, the formulation of MT in combination with CHT–CMC is proven to be an efficient biocompatible agent with potential in the extension of shelf life, leading to quality control of pepper under postharvest storage.