Valorization of freshwater crab shell residues to chitosan for postharvest quality of mango (Mangifera indica L.) by fruit coating

Freshwater crab shells (Somanniathelphusa dugasti) are abundant in inland areas and rich in chitosan, which can be extracted and utilized. This study investigated the characteristics of chitosan from freshwater crab shells (FC-chitosan) and its impact on extending the shelf life of Nam Dok Mai mangoes (Mangifera indica L.). The FC-chitosan had a high degree of deacetylation (99.15 %), thereby enhancing solubility and reactivity for a uniform coating, and a low ash content (0.75 %), minimizing the interference effects on mechanical strength and transparency, both of which could contribute to its potential use as a well-adhering coating material. The FC-chitosan film exhibited superior properties as a coating film, with relatively higher transparency (25.09 % T/mm), tensile strength (21.57 MPa), and elongation (76.09 %) compared to commercially available marine crab chitosan. Mango fruits coated with 2.0 % (w/v) FC-chitosan demonstrated appropriate postharvest quality, with lower weight loss and maintained peel color, fruit firmness, titratable acidity, and ascorbic acid during storage at room temperature (30 ± 5 °C) for up to 11 days. The results suggest that FC-chitosan is effective as a coating material for delaying ripening and extending the shelf life of mangoes. The novelty of using chitosan derived from freshwater crab shells lies in its unique properties and its sustainable use of underutilized byproducts.