Performance Characteristics of Chitosan ε-Polylysine Composite Films and Their Application in Tuna Shelf-Life Extension

This study systematically evaluates the synergistic preservation effects of chitosan-ε-polylysine (ε-CS-PL) composite films on refrigerated yellowfin tuna ( Thunnus albacares ). Through quantitative analysis of myoglobin (Mb) oxidation, microbial growth, lipid stability, and biochemical spoilage indicators, we demonstrate that ε-PL significantly inhibits Mb oxidation, retaining 49.1 g/kg metmyoglobin (Met) content in the ε-PL-2 group by day 8—nearly double that of untreated controls (26.5 g/kg). The composite films reduced total volatile basic nitrogen (TVB-N) accumulation by 43% (25.6 vs. 44.7 mg/100g in controls) and suppressed microbial counts to 6.3 log CFU/g (vs. 7.8 log CFU/g in controls) through ε-PL’s broad-spectrum antimicrobial action. Lipid oxidation (TBA values: 0.55 vs. 0.73 mg/100g) and nucleotide degradation ( K value: 22.3 vs. 36.7) were markedly delayed, while color stability ( a* value: 5.79 vs. 2.97) was preserved. These results establish CS-ε-PL films as a multifunctional preservation system, combining chitosan’s barrier properties with ε-PL’s antioxidant and antimicrobial activities to extend tuna shelf life by > 40% under refrigeration (4°C).