Indicator films based on nano-ZnO, purple tomato anthocyanins and polyvinyl alcohol for application in chicken packaging

Nano-ZnO/purple tomato anthocyanin (PTA)/polyvinyl alcohol (PVA) composite films were prepared by solution casting, with nano-ZnO content varied from 0% to 10% relative to the PVA matrix. The influence of nano-ZnO content on the films was evaluated, covering mechanical properties, moisture content, water vapor transmission rate, swelling rate, antioxidant activity, color response, X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), and thermal stability, to assess their potential as smart food labels. The results revealed that the composite films displayed pH-responsive behavior. With increasing nano-ZnO concentration, the tensile strength of the films increased from 29.2 MPa to 39.2 MPa, while the elongation at break was enhanced by 26.4%. The antibacterial inhibition rates of films containing 0%-10% nano-ZnO against Staphylococcus aureus and Escherichia coli ranged from 30.54% to 93.82% and from 23.41% to 88.31%, respectively. Moisture content, water vapor transmission rate, thermal stability, and antibacterial activity exhibited gradual improvement, whereas antioxidant capacity and swelling rate decreased from 68.1% to 38.3% and from 127% to 42%, respectively. When applied in chicken breast packaging, composite films with 0% and 5% nano-ZnO showed noticeable color difference changes across different spoilage stages of the chicken breast, indicating their potential as freshness indicator labels.