Chitosan-alginate-cellulose nanocrystal bio-nanocomposite coating with isotropic-anisotropic microdomains enhances papaya shelf life and inhibits Colletotrichum gloeosporioides

This study developed a chitosan-alginate edible bio-nanocomposite (EBNC) coating, reinforced with a cellulose nanocrystal (CNC)-stabilized ginger essential oil (GEO) Pickering emulsion, for postharvest preservation of papaya (Carica papaya L.). The EBNC showed a particle size of 825.32 ± 35.58 nm (PDI 0.491) and a zeta potential of -34.2 ± 3.63 mV, while FTIR and DSC indicated extensive hydrogen bonding and thermal stability. Microscopy revealed a hybrid isotropic-anisotropic microstructure, in which CNC-induced anisotropic domains are proposed to increase diffusion tortuosity and thereby improve barrier performance. Cytocompatibility was concentration- and time-dependent, with >80% NIH-3T3 viability at ≤250 μg/mL after 48 h. On papaya stored under ambient conditions, the coating significantly reduced weight loss (p 1000 μg/mL), and fungal regrowth after subculture indicated a predominantly fungistatic effect. Mechanistic assays showed membrane permeabilization (PI uptake 44.58 ± 9.67%), nucleic acid leakage (51.02 ± 8.67%), and limited ergosterol inhibition (10.83%), identifying the membrane, rather than ergosterol biosynthesis, as the principal target. Overall, the EBNC combines barrier-related quality preservation with moderate fungistatic activity, offering a promising postharvest strategy for papaya. However, the findings are limited to ambient storage and in vitro antifungal assays; in vivo disease challenge, sensory acceptability, and food-safety assessment remain to be established.