pH-responsive intelligent edible films based on sodium alginate–pectin reinforced with chitosan nanoparticles, green-synthesized TiO2 nanoparticles, and Azarshahr red onion peel anthocyanins

This study developed pH-sensitive edible nanocomposite films based on a sodium alginate–pectin matrix reinforced with chitosan nanoparticles and green-synthesized TiO₂ nanoparticles, incorporating anthocyanin extract from Azarshahr red onion peel as a natural indicator. The addition of nanoparticles significantly improved tensile strength, reduced water solubility, and lowered water vapor permeability compared to the control film. Films containing anthocyanins exhibited rapid and reversible color changes (within 1 min), transitioning from red/orange in acidic–neutral conditions to green/brown in alkaline environments, enabling real-time visual monitoring of food spoilage. The optimal formulation (10% anthocyanin extract) demonstrated strong antioxidant activity (>75% DPPH scavenging), notable antibacterial effects (inhibition zones of 13 mm against Escherichia coli and 16 mm against Staphylococcus aureus ), enhanced UV-barrier properties, and minimal water vapor transmission. Structural analyses (SEM, FTIR, XRD) confirmed uniform nanoparticle dispersion and retention of anatase TiO₂. Migration levels were below regulatory limits, and cytotoxicity tests indicated negligible toxicity. These findings highlight the potential of this sustainable nanocomposite system as an eco-friendly intelligent packaging material while valorizing agricultural waste.