Intelligent indicator films based on cold plasma-modified chitosan loaded with curcumin-resveratrol nanoemulsions: pH-responsive mechanism, colorimetric performance and application for tilapia freshness monitoring.

Food safety risks associated with spoilage and plastic packaging have driven the development of sustainable intelligent packaging systems. In this study, zein-curcumin-resveratrol‑sodium alginate nanoemulsions were incorporated into chitosan films to construct pH-responsive active indicator films. Cold plasma (CP) modification was applied to regulate surface properties and enhance sensing performance. CP modification increased surface roughness and active sites, improving the interaction between films and volatile amines. The 30 kV CP-modified film exhibited optimal comprehensive properties, with improved mechanical strength (tensile strength of 5.36 ± 0.18 MPa and elongation at break of 46.95 ± 3.14%), antioxidant activities (73.81 ± 1.50% for DPPH and 70.26 ± 1.41% for ABTS), pH responsiveness, barrier properties and UV protection. Moreover, colorimetric responses (ΔE and a* values) showed a significant positive correlation with tilapia TVB-N accumulation (R2 > 0.95), verifying the quantitative relationship between film discoloration and fish freshness deterioration. This study provides a practical intelligent packaging strategy for real-time aquatic product quality monitoring.