Broccoli leaf-derived carbon dots reinforced chitosan/gelatin film as UV-blocking, antioxidant, and antibacterial films for food packaging

Abstract

Carbon dots (CDs) were synthesized from broccoli leaf waste via a hydrothermal process at 180 °C for 8 h and characterized by UV-Vis, PL, FTIR, XRD, TEM, and zeta potential analyses. The CDs exhibited quasi-spherical morphology with diameters of 5–15 nm, a polycrystalline structure composed of amorphous and graphitic domains, and diverse surface functional groups (–OH, –COOH, –NH₂, CO, and sulfur-containing moieties), conferring their great aqueous dispersibility and photoluminescent stability under varying pH (2–12) and NaCl concentrations (0.0–2.0 M). The CDs were subsequently incorporated into chitosan/gelatin films at loadings of 0–10% relative to the polymer mass. At 5% loading, the films displayed a great tensile strength of 80.32 MPa, notable 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging efficacy of ∼90%, and significantly low water solubility (∼13%). Moreover, the composite films exhibited reduced water swelling, enhanced thermal stability, greater UV-blocking capacity, and improved antibacterial activity against Escherichia coli and Staphylococcus aureus as compared to the neat chitosan/gelatin film. Practical studies demonstrated that the CDs-loaded films effectively protected green apples from UV-induced damage and significantly extended the shelf life of strawberries, outperforming commercial polyethylene (PE) film. All these results highlight the potential of broccoli leaf-derived CDs as effective nanofillers for the fabrication of multifunctional chitosan/gelatin-based food packaging films.