Construction of caffeic acid-modified chitosan immobilized nanosilver system and its application in strawberry preservation

Caffeic acid-modified chitosan (CCS) was successfully prepared as a dispersant and reducing agent for nanosilver. • AgNPs@CCS has excellent antimicrobial activity and biocompatibility. • APCCS composite films exhibit strong antioxidant properties. • The APCCS-2 composite film achieves long-lasting antimicrobial activity and can inhibit bacterial reproduction within 60 h. • APCCS composite films extended the shelf life of strawberries to the 9th day under 4 °C storage conditions. The massive release of silver nanoparticles poses a cumulative toxicity threat to the environment and living organisms. In this study, we have for the first time utilized the strong chelating effect of catechol groups in caffeic acid-modified chitosan (CCS) toward Ag + to achieve the immobilization and reduction of nanosilver (AgNPs@CCS) via a green synthesis method. This approach enables controlled Ag + release and enhances the biocompatibility of AgNPs@CCS: Ag + release was only 0.298 ± 0.004 μg/mL after 72 h. Hemolysis rates remained below 5% at 1024 μg/mL, and cell viability exceeded 80% at 250 μg/mL. Furthermore, to investigate the application of AgNPs@CCS in fruit preservation, we incorporated it as an antimicrobial filler into CCS and polyvinyl alcohol matrices to prepare composite films with excellent antimicrobial and preservation properties. Results demonstrated that the incorporation of AgNPs@CCS significantly enhanced the composite the mechanical properties, antioxidant capacity, and barrier performance of film. The APCCS-2 composite film exhibited antibacterial inhibition rates exceeding 97% against both E . coli and S . aureus , effectively suppressing bacterial proliferation for up to 60 h. Finally, the APCCS composite film extended the shelf life of strawberries stored at 4 °C to 9 days. And the weight loss rate of all APCCS composite films was greater than 19% on the 28th day, indicating that they have excellent degradation performance. It is a highly promising freshness-preserving packaging film. Download: Download high-res image (346KB) Download: Download full-size image