Intelligent active double-layer film based on ɛ-polylysine-anthocyanin co-pigmentation effect and Zn‑carbon dot construction: Effects on pork preservation, freshness monitoring and soil microbiology

Abstract

In this study, a double-layer film system was constructed with potato starch/k-carrageenan (PC) loaded with ε-polylysine-anthocyanin (ɛPL-ACN) co-pigmentation as the inner indicator layer and chitosan/gelatin (CG) loaded with ZnO-doped carbon dots (ZnCDs) as the outer protective layer. The system was designed to realize the triple functions of long-lasting bacterial inhibition, dynamic monitoring and environmental regeneration for meat packaging. When the loading concentration of ZnCDs was adjusted to 7%, the film exhibited the highest antioxidant activity (DPPH: 75.80 ± 4.01% and ABTS: 78.09 ± 2.29%), antibacterial effect (S. aureus inhibition rate: 95.27 ± 2.17% and E. coli inhibition rate: 92.23 ± 2.24%), mechanical strength (tensile strength: 21.44 ± 0.47 MPa and elongation at break: 20.53 ± 0.81%), and light stability (ΔE: 14.71 ± 0.71). In particular, the PC-ɛPL-ACN/CG-ZnCDs-7% film exhibits excellent pH and ammonia response, which allows for the visual determination of pork freshness by color change. In terms of freshness, it extends the shelf life of pork by 4 d at 4 °C and 12 h at 20 °C. In addition, the film color difference value (ΔE) was strongly correlated with pork pH, total volatile base nitrogen and total viable count (R² > 0.95), which combined with smartphone RGB analysis technology can realize real-time monitoring of pork freshness. Compared with polyethylene films, PC-ɛPL-ACN/CG-ZnCDs-7% films not only have good biodegradability, but also effectively regulate the soil microbial community structure and promote the growth of crops such as Brassica rapa L., demonstrating significant environmental sustainability advantages.