Development of sodium alginate–gelatin films containing Toona sinensis extract for extending the shelf life of strawberries

Herein, we developed sodium alginate–gelatin films incorporated with various concentrations of Toona sinensis extracts (1:20, 1:10, and 1:5 SGTS films) and evaluated their physicochemical properties, bioactivity, and packaging potential. The incorporation of T. sinensis extracts significantly altered the films' structure and optical properties: thickness increased from 0.0521 to 0.0864 mm, lightness decreased from 88.88 to 50.56, and ultraviolet transmittance (200–380 nm) was nearly blocked. Mechanical flexibility was improved, and a reduced contact angle indicated enhanced hydrophilicity. Furthermore, bioactivity was notably enhanced: total phenol content increased from 6.56 to 47.86 mg GAE/g, DPPH-scavenging activity reached 91.8 %, and ABTS + -scavenging activity reached 92.34 %. Antibacterial effects were strengthened, with inhibition zones against Escherichia coli reaching 12.31 ± 0.98 mm (SGTS 1:10) and 13.34 ± 0.21 mm (SGTS 1:5), and against Staphylococcus aureus reaching 11.39 ± 0.70 mm (SGTS 1:10) and 12.50 ± 0.53 mm (SGTS 1:5). Scanning electron microscopy confirmed bacterial membrane disruption, and storage tests demonstrated that SGTS films effectively maintained strawberries' appearance, firmness, pH, and sensory quality while reducing weight loss. Therefore, SGTS films exhibit multifunctional antioxidant, antibacterial, and preservation capabilities as an eco-friendly bioactive packaging material.