Effects of carboxymethyl cellulose and chitosan bilayer edible coating on postharvest quality of citrus fruit

There is increasing public interest in development of edible natural biodegradable coatings to replace the currently used commercial synthetic waxes for maintaining postharvest quality of citrus fruit. We tested the efficacy of a newly developed polysaccharide-based edible bilayer coating comprising carboxymethyl cellulose (CMC) and chitosan in preserving postharvest quality of various citrus fruit, including 'Or' and 'Mor' mandarins, 'Navel' oranges, and 'Star Ruby' grapefruit after simulated storage and marketing. In all citrus species, it was found that the CMC/chitosan bilayer coating was equally effective as the commercial polyethylene wax in enhancing fruit gloss. Furthermore, the CMC/chitosan bilayer coating slightly increased fruit firmness, especially of oranges and grapefruit, but was mostly not effective in preventing post-storage weight loss. Both the CMC/chitosan bilayer coating and the commercial wax had no significant effects on juice total soluble solids and acidity levels, and had similar effects on gas permeability, as indicated by only slight increases in internal CO₂ levels and in juice ethanol accumulation after storage. Sensory analyses revealed that neither the CMC/chitosan bilayer coating nor the commercial wax coating had any deleterious effects on flavor preference of 'Navel' orange and 'Star Ruby' grapefruit. However, application of the commercial wax, and moreover the CMC/chitosan bilayer coating, resulted in a gradual decrease in flavor acceptability of 'Or' and 'Mor' mandarins because of increased perception of off-flavors. Overall, we showed that the CMC/chitosan bilayer edible coating sufficiently enhanced fruit gloss, but was not effective in preventing postharvest weight loss. Furthermore, flavor quality was slightly impaired in mandarins but not in oranges and grapefruit.