Pullulan/sodium alginate-based color-indicating film combined with Vaccinium vitis-idaea anthocyanins and ZnO nanoparticles for monitoring milk freshness.

Pullulan/sodium alginate (Pul/SA)-based smart and functional freshness indicator films were prepared by adding red anthocyanin extracts and zinc oxide nanoparticles (ZnO). The anthocyanin was extracted from Vaccinium vitis-idaea, and ZnO was synthesized using a simple hydrothermal method. The Vaccinium vitis-idaea anthocyanin (ACNs) and ZnO were evenly dispersed in the polymer matrix to form a compatible film with the Pul/SA polymer. The addition of anthocyanins and ZnO significantly increased the UV-blocking and mechanical properties of the film without significantly changing the transparency of the film. In addition, the composite film showed strong antioxidant and strong bactericidal properties, and the antioxidant function was mainly attributed to the ACNs, and the antibacterial function was attributed to ZnO. The ACNs and ACNs-added films showed excellent pH-responsive color-change properties as well as good color stability and reversibility. However the alkalized Pul/SA/ACNs/ZnO (a-Pul/SA/ACNs/ZnO) film in the freshness monitoring of pasteurized milk also showed a color difference from dark brown, brown to yellow, indicating a decrease in milk quality accompanied by a decrease in pH and an increase in acidity. The composite film was used in the development of active and intelligent food packaging.