Bioactive κ-Carrageenan–ε-Poly-L-Lysine Edible Coating Synergistically Enhances Quality and Shelf Life of Rainbow Trout (Oncorhynchus mykiss) Fillets under Refrigerated Storage

This study investigated the synergistic effects of the kappa-carrageenan–epsilon-poly-L-lysine (KCA–ε-PL) bioactive edible coating on the quality and shelf life of rainbow trout ( Oncorhynchus mykiss ) fillets during 15 days of refrigerated storage (4°C). The treatments included KCA, ε-PL, KCA + ε-PL, and an untreated control. The KCA–ε-PL coating significantly (p < 0.05) suppressed mesophilic bacterial growth, limiting the increase from 1.8 to 7.5 log CFU/g, whereas counts reached 10.95 log CFU/g in the control. Chemical spoilage indicators showed a similar trend: total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARS) rose more gradually in the KCA–ε-PL group (from 10.9 to 24.4 mg/100 g and from 0.3 to 1.6 mg MDA/kg, respectively) compared with the control (43.3 mg/100 g and 2.5 mg MDA/kg). Sensory deterioration was also delayed, as the KCA–ε-PL coated fillets maintained an overall acceptability score of 2.2 (still within the “acceptable” range) after 15 days, whereas the control samples declined to a score of 1, indicating complete rejection. Collectively, these results confirm that the synergistic antimicrobial and antioxidative activities of KCA–ε-PL markedly improve quality attributes and extend the shelf life of rainbow trout fillets by approximately five days under refrigerated storage.