Carbon dots and cellulose nanocrystal-incorporated chitosan composite films with enhanced gas selectivity and photodynamic antibacterial properties for fruit preservation.

Winter jujube is prone to rapid ripening and deterioration during postharvest storage and transportation. This study developed a multifunctional chitosan (CS) composite film incorporating dialdehyde cellulose nanocrystal (DCNC) and carbon dots (CDs) derived from walnut green husks. DCNC functioned as cross-linking filler, while CDs served as active nanofillers. The CS composite film containing 3 wt% DCNC and 3 wt% CDs (CS/DCNC/CDs-3 %) exhibited significant improvements in UV-blocking, mechanical strength, gas barrier, and thermal stability, attributing to the formation of a dense film structure and synergistic effect of Schiff base and hydrogen bonding interactions among film components. Notably, this composite film demonstrated a high CO2/O2 selectivity of 14.1, facilitating the creation of an ideal atmosphere inside the package. This composite film exhibited remarkable antioxidant activity and displayed potent antibacterial capacity through photocatalytic ROS generation, achieving inhibition rates of 90.8 % against S. aureus and 86.8 % against E. coli. Additionally, this film showed favorable biosafety and biodegradability, addressing food safety and environmental concerns. Postharvest preservation tests confirmed that this film assisted by light exposure effectively regulated physiological metabolism and delayed the ripening of winter jujube, highlighting its potential as an active modified atmosphere packaging material for perishable fruit preservation.