Tannic acid mediated surface functionalization of polylactic acid nanofiber films for in situ AgNPs immobilization: antioxidant, antibacterial and fresh-keeping properties

The application of biodegradable and environment-friendly packaging materials with antioxidant and antibacterial activities is urgent and essential for food fresh-keeping. In this work, surface-functionalized biodegradable electrospun polylactic acid (PLA) nanofiber films were fabricated via a simple two-step strategy, which integrated the bioinspired coating of tannic acid (TA, a naturally occurring plant polyphenol) and the subsequent in situ immobilization of silver nanoparticle (AgNPs). The TA coating endowed the nanofiber films with excellent antioxidant activity, while simultaneously functioning as reductant and stabilizer for the in situ synthesis of AgNPs from silver source (silver nitrate), and consequently, the reduction process did not necessitate the incorporation of extra reducing or stabilizing agents. The surface morphology and chemical composition of the functionalized PLA nanofiber films were characterized by SEM, EDX and XPS. The TA-mediated surface modification increased the nanofiber diameter compared to pristine PLA film, and the generated AgNPs made the nanofibers much rougher. The fabricated PLA-TA@AgNPs nanofiber films exhibited enhanced mechanical properties, with tensile strength increasing and ∼ 193 % compared to pristine PLA films. Furthermore, the introduction of TA coating impressively imparted the films with excellent antioxidant activity, demonstrating a potent scavenging effect on DPPH and ABTS free radicals. In vitro antibacterial assay showed excellent antibacterial ability of the PLA-TA@AgNPs nanofiber films against Escherichia coli and Staphylococcus aureus. Furthermore, the functional PLA-TA@AgNPs nanofiber films extended the shelf life of strawberries to at least 8 days at room temperature, as indicated by the appearance, weight loss and firmness loss, demonstrating great potential for use in fresh-keeping packaging applications.