Performance characteristics of chitosan ε-polylysine composite films and their application in tuna shelf-life extension

Introduction Yellowfin tuna ( Thunnus albacares ) is highly susceptible to microbial spoilage, lipid oxidation, and myoglobin (Mb) oxidation during refrigerated storage, which severely limits its shelf life. The development of natural, multifunctional preservation systems is therefore essential for maintaining tuna quality. Methods Chitosan-ε-polylysine (CS-ε-PL) composite films with different ε-PL concentrations were applied to refrigerated yellowfin tuna. Preservation efficacy was systematically evaluated by monitoring Mb oxidation, microbial growth, lipid oxidation, nucleotide degradation, color stability, and biochemical spoilage indicators during storage at 4 °C. Results The CS-ε-PL composite films significantly delayed quality deterioration compared with untreated controls. ε-PL markedly inhibited Mb oxidation, with the ε-PL-0.15 group retaining 49.1 g/kg metmyoglobin (Met) by day 8, nearly double that of the control group (26.5 g/kg). Lipid oxidation (TBA: 0.55 vs. 0.73 mg/100 g) and nucleotide degradation ( K value: 22.3 vs. 36.7) were substantially suppressed, while color stability was better maintained ( a * value: 5.79 vs. 2.97). The accumulation of total volatile basic nitrogen (TVB-N) was reduced by 43% (25.6 vs. 44.7 mg/100 g). Moreover, microbial growth was effectively controlled, with total viable counts limited to 6.3 log CFU/g compared with 7.8 log CFU/g in the control group. Discussion The enhanced preservation performance of CS-ε-PL films is attributed to the synergistic effects between the physical barrier properties of chitosan and the broad-spectrum antibacterial and antioxidant activities of ε-polylysine. This multifunctional composite system effectively retards oxidative reactions and microbial proliferation, thereby significantly extending the refrigerated shelf life of yellowfin tuna.