Optimization of Chitosan/Modified Chitosan–Silver(I) Composite Film and Application to Strawberries

Fresh fruits are prone to spoilage due to microbial contamination and moisture loss, highlighting the need for effective packaging materials with strong barrier and antimicrobial functions. In this work, a bilayer composite film with antimicrobial and preservative properties was fabricated using the solution casting method, consisting of an inner chitosan (CS) layer and an outer complex layer of chitosan-2-pyridinecarboxaldehyde-Ag(I) (CS-PCA-Ag(I)). Preparation conditions were optimized via single-factor experiments combined with response surface methodology. The resulting composite film showed significantly enhanced mechanical properties, with tensile strength of 38.52 ± 2.07 MPa and elongation at break of 67.32 ± 1.47%, as well as a low water vapor permeability of 2.81 × 10−7 g·m−1·h−1·Pa−1. It also exhibited strong antibacterial activity against Staphylococcus aureus and Escherichia coli, with inhibition zone diameters of 19.8 ± 0.3 mm and 15.6 ± 0.2 mm, respectively. Strawberry preservation tests demonstrated that the CS/CS-PCA-Ag(I) film effectively suppressed microbial growth and reduced fruit weight loss (8.27 ± 0.42% after 5 days), thereby extending the shelf life of strawberries. Cytotoxicity evaluation and silver ion migration analysis further confirmed the film’s good biocompatibility and safety. Collectively, the CS/CS-PCA-Ag(I) composite film holds considerable promise for fresh food preservation applications.