Comparison of the Structural Characteristics and Functional Performances of Chitosan-Based Active Packaging Films Loaded with Three Varieties of Water Chestnut (Trapa bispinosa Roxb.) Shell Powder

Water chestnut (Trapa bispinosa Roxb.) shell is an underutilized fruit processing by-product. Here, three varieties of water chestnut shells (green, red, and black) were pulverized into powder and individually loaded into a chitosan (CS)-based matrix to develop active packaging films via solvent casting. The structural characteristics, physical and functional properties, and minced pork preservation effects of water chestnut shell powder (WCSP)-loaded films were systematically compared with those of the CS film. Results showed that WCSP was rich in lignocellulose and polyphenols. Green and red WCSP with sheet-like morphology were uniformly dispersed in the CS matrix, whereas black WCSP with a bulky, block-like morphology was locally distributed within the matrix. Compared with the CS film, WCSP-loaded films showed higher tensile strength, water vapor permeability, and antioxidant and antimicrobial activities but lower light transmittance, elongation at break, moisture content, water solubility, and swelling ratio. When minced pork was wrapped in CS film and WCSP-loaded films, its shelf life was extended to 4 and 6 days, respectively. Notably, the film incorporated with green WCSP showed the highest antioxidant and antimicrobial activities as well as the optimal pork preservation effect. This study confirms that the water chestnut cultivar significantly affects film properties, providing a new route for high-value utilization of WCSP.