A Smart Food Freshness Indicator Film for Shrimp and Pork with the Higher Visuality, Barrier, Flame Retardancy, and Antibacterial Effects

A fully natural and biodegradable film (MC₅/ZA₅-DE_3%) was developed using methylcellulose (MC) (a plant-based biopolymer with excellent film-forming properties and biocompatibility), zinc alginate (ZA) (derived from brown seaweed, served as a biodegradable component with excellent film-forming properties and enhanced mechanical strength through cross-linking with Zn²⁺), and anthocyanin-rich dragon fruit peel extract (DE) (a natural antioxidant with pH sensitivity and colorimetric properties). The film exhibited distinct color changes from purple to green across a range of pH-buffered solutions, demonstrating its pH sensitivity. The antimicrobial activity of the film showed a significant inhibition zone against Staphylococcus aureus and Escherichia coli, with a 99.99% bacterial reduction. The incorporation of Zn²⁺ also improved the flame retardancy of the film, reducing flammability by 34.5%. Optical analysis showed that the MC₅/ZA₅-DE_3% film exhibited excellent UV-blocking performance due to the synergistic effect of Zn²⁺ and anthocyanins, which enhanced UV absorption (200–400 nm) and reduced visible light transmittance, making it an effective UV barrier with acceptable transparency for packaging. Furthermore, the film served as an intelligent indicator of food spoilage, changing color from purple to green with increased storage time, indicating elevated total volatile basic nitrogen (TVB-N) levels. The MC₅/ZA₅-DE_3% film is non-toxic and suitable for large-scale industrial production, highlighting its potential for intelligent food packaging applications.