Bentonite and gallotannin-mediated silver nanoparticle-modified chitosan biofilms for food preservation

In view of the increasingly severe environmental hazards posed by traditional plastic packaging materials, this study develops a biodegradable chitosan (CS) film to address deficiencies in water solubility and mechanical properties, thereby promoting its wide application in the field of food packaging. A novel antioxidant, antibacterial, and biodegradable food packaging film was synthesized using natural bentonite (Bt) and gallic acid (GA) - mediated silver nanoparticles (AgNPs). This is the first study to integrate Bt, GA, and in-situ-synthesized AgNPs into chitosan films for synergistic antioxidant/antibacterial enhancement. Specifically, chitosan was modified with gallic acid, which significantly improved the water solubility of chitosan. Subsequently, GA reduces Ag⁺ in situ to form AgNPs using the modified chitosan. SEM analysis indicated that the diameter of the synthesized AgNPs ranged from 30 to 100 nm. By means of the solution casting method, the modified chitosan was compounded with AgNPs and Bt. CSGA/Bt/AgNPs film exhibited excellent water vapor and ultraviolet (UV) barrier properties. In terms of mechanical properties, the strength of the pure CS film was 17.28 MPa, while that of the CSGA/Bt/AgNPs film reached 18.56 MPa, indicating a good interaction among CS, GA, Bt, and AgNPs. Experimental results demonstrated that the film had significant antibacterial activity against S. aureus and E. coli, demonstrating great application potential in the field of food packaging.