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

## TL;DR

This study shows that chitosan-ε-polylysine films can significantly extend the shelf life of yellowfin tuna by reducing spoilage and oxidation during refrigeration.

## Contribution

The paper introduces a novel chitosan-ε-polylysine composite film with synergistic antibacterial and antioxidant properties for seafood preservation.

## Key findings

- CS-ε-PL films reduced metmyoglobin levels by nearly double compared to controls after 8 days of storage.
- Lipid oxidation and nucleotide degradation were significantly suppressed in treated tuna samples.
- Microbial growth was effectively controlled, with lower viable counts in the treated group.

## Abstract

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.

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.

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.

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.