Chitosan films functionalized with carrier-free nanoparticles: structure-property relationships revealed by...

The development of biodegradable active packaging films with both desirable functional performance and clear structure-property mechanisms is important for improving food preservation. In this study, carrier-free berberine-quercetin self-assembled nanoparticles (BQNPs) were prepared using a solvent-antisolvent method and incorporated into a chitosan matrix as active nanofillers to construct multifunctional composite films (CS@BQNP). The optimized BQNPs showed a suitable particle size (Z-Ave = 91.58 ± 0.51 nm), a narrow particle size distribution (PDI = 0.166 ± 0.016), and good stability, which favored their uniform dispersion and functional performance in the chitosan films. The incorporation of BQNPs increased the tensile strength of the chitosan film by 15.02 MPa and reduced the moisture content by 4.67%. The CS@BQNP films also exhibited improved water vapor barrier performance, stronger UV-shielding ability, and markedly enhanced antioxidant activity. In addition, the antibacterial activity of CS@BQNP films against Staphylococcus aureus and Escherichia coli increased by 23.6% and 64.3%, respectively. In the tomato preservation assay, CS@BQNP films delayed quality deterioration during storage. Multiscale simulations suggest that berberine and quercetin may form relatively stable self-assembled aggregates through a combination of electrostatic attraction, hydrogen bonding, hydrophobic interactions, and π-π stacking. After incorporation into the chitosan matrix, the simulation results indicate that BQNPs may interact with chitosan chains mainly through hydrogen bonding and hydrophobic interactions. These interactions are consistent with the formation of a more compact composite network and may contribute to the improved mechanical properties, barrier performance, and optical shielding ability of the composite films.