Alginate-Based Emulsion with Oregano Essential Oil for the Preservation of Frozen–Thawed Ready-to-Cook Hake Fillets as a Model System

Fish are nutritionally valuable foods but are also highly perishable, representing a major research focus for the development of effective preservation strategies to delay spoilage while maintaining microbiological acceptability. In this context, edible coatings have gained increasing attention as clean-label tools to extend the shelf life of perishable foods. In this study, an alginate-based emulsion containing oregano essential oil (OEO) was applied to commercial frozen–thawed ready-to-cook (RTC) hake fillets, intentionally selected as a reproducible model system to evaluate coating performance under refrigerated conditions. Coated and uncoated fillets, stored at 4 °C for up to 7 days, were monitored over time for microbiological and physicochemical parameters, including microbial loads, pH, weight loss, and lipid oxidation (TBARS). Compared to uncoated samples, fillets treated with the alginate–OEO emulsion exhibited a marked delay in spoilage-related microbial growth, with a consistent inhibition of Pseudomonas spp. throughout the experimental period, while maintaining microbiological acceptability. Emulsion-based coated fillets also exhibited reduced lipid oxidation, a more uniform surface appearance with only minor visible color changes, and the absence of unpleasant off odors during the refrigerated storage. Overall, the results demonstrate that the alginate–OEO coating could represent an effective strategy for improving the microbiological and oxidative stability of RTC fish fillets under refrigerated conditions, with potential implications for extended shelf life and a reduction in food waste.