Development of Plasma-Modified PLA/Chitosan-Zein Nanoparticle Bilayer Films for Enhanced Rainbow Trout Shelf-Life

This study evaluated quality preservation of rainbow trout (Oncorhynchus mykiss) fillets using an active bilayer film composed of cold plasma-treated polylactic acid (PLA) and chitosan-zein nanoparticles (Chit/Z-NPs). Packaging performance was compared with conventional low-density polyethylene (LDPE) over 12 days at 4°C. The bilayer film significantly delayed chemical, microbial, and sensory deterioration. By Day 12, total volatile basic nitrogen (TVB-N) reached 39.22 mg N/100 g in bilayer samples versus 68.14 mg N/100 g in LDPE controls, with LDPE exceeding EU freshness limits while bilayer samples remained acceptable. Thiobarbituric acid reactive substances (TBARS) were lower in bilayer samples (0.192 mg MDA/kg) compared to LDPE (0.265 mg MDA/kg), indicating reduced lipid oxidation. Color analysis confirmed superior visual quality preservation, with lower total color difference (ΔE ∼12 vs. ∼23), whiteness index changes (WI: 65.88-72.10 vs. 81.36), and yellowness index increases (YI: 10.54-11.38 vs. 12.98). Total viable counts in LDPE samples exceeded spoilage thresholds (10.88 log₁₀ MPN/g), while bilayer films limited microbial growth to 6.90 log₁₀ MPN/g. Sensory evaluation demonstrated that only bilayer-packaged fillets maintained acceptability above consumer rejection thresholds (4.03 vs. 2.34 for LDPE). Results demonstrate that PLA/Chit-Z-NPs bilayer films effectively preserve quality attributes, providing a sustainable alternative to conventional packaging for fresh fish.