Natural deep eutectic solvent-based pectin-chitosan composite hydrogel films: A novel pH-responsive color indicator for food packaging systems

This study presents a novel intelligent, biodegradable hydrogel film for food packaging, based on a pectin–chitosan matrix, integrated with Hibiscus sabdariffa extract and a natural deep eutectic solvent (DES; choline chloride–lactic acid). Anthocyanins from H. sabdariffa enabled reversible color changes (red–purple–yellow) across pH 2–10, allowing real-time freshness monitoring. Mechanical testing revealed that DES enhanced film flexibility by increasing elongation at break and reducing tensile strength. FTIR and XRD analyses supported these findings by showing reduced hydrogen bonding interactions and a more disordered amorphous structure, which are structural features commonly associated with improved polymer chain mobility. FESEM revealed a compact morphology, with increased roughness due to chemical compounds in the extract. Antioxidant activity improved with H. sabdariffa, as shown by DPPH and ABTS assays, suggesting potential for oxidative stability enhancement in food packaging applications. However, DES raised water vapor permeability by 194 %, indicating a considerable reduction in barrier performance. These hydrogel films are envisioned for use as direct-contact layers in perishable food packaging, enabling consumers to monitor freshness through visible color changes. This synergistic system offers excellent pH responsiveness, antioxidant functionality, and mechanical flexibility, supporting its application in smart food packaging.