Sodium alginate/chitosan-based intelligent bilayer film with antimicrobial activity for pork preservation and freshness monitoring

A pH-sensitive bilayer film with antioxidant and antibacterial activities was successfully prepared by anchoring anthocyanins (ACNs) with sodium alginate (SA) as the sensing inner layer and incorporating TiO2 in chitosan (CS) as the protective outer layer. ACNs in the inner layer were immobilized under acidic conditions while released under alkaline conditions because of the pH sensitivity of SA molecules. The incorporation of TiO2 improved the color stability of the ACNs, and the film exhibited a wide range of color variations at pH 2-13 with Delta E>5. FT-IR confirmed the existence of hydrogen bonds among the components, and the tensile strength (TS) and elongation at break (EB) of the film reached 24.32 MPa and 38.58%, respectively. Moreover, the bactericidal rates of the film towards E. coli and S. aureus were 99.23% and 97.49%, respectively. The bilayer film could extend the pork's shelf life for 40 and 96 h at 20 degrees C and 4 degrees C, and monitor the pork quality in real-time. Therefore, the ACNs@SA + CS/TiO2 bilayer film is promising for meat preservation and freshness monitoring.