Anthocyanin loaded composite gelatin films crosslinked with oxidized alginate for monitoring spoilage of flesh foods

In this study, we developed composite films by crosslinking gelatin with oxidized alginate and anthocyanin through Schiff base linkage, electrostatic interaction and hydrogen bonds. Physicochemical properties of the films can be adjusted by changing the concentration of oxidized alginate. The tensile strength of the film containing 10 wt% oxidized alginate reached 45 MPa, surpassing that of films with 1 wt% and 3 wt% oxidized alginate. As the concentration of oxidized alginate increased, the swelling ratio of the films decreased. The release rate of anthocyanin from the film with 10 wt% oxidized alginate in pH 7.0 water was 15.3%, significantly lower than that of the film lacking oxidized alginate (release rate 42.1%). The antioxidant properties of the composite gelatin films with anthocyanin were about 40% in DPPH radical scavenging activity. Additionally, the color of film with 3 wt% oxidized alginate changed from light pink to green in a solution with a pH range from 3 to 11 and the film was sensitive to acidic or basic vapors. This color-changing capability makes the film a potential indicator for detecting spoilage in fish, pork, and chicken, manifesting color changes from light pink to light green. Furthermore, the composite films exhibited biodegradable characteristics in soil, lakes, and simulated seawater. Notably, the film containing 10 wt% oxidized alginate demonstrated greater stability compared to the film without oxidized alginate. The gelatin film with pH responsive and biodegradable properties can be potentially used in the field of intelligent food packaging.