Dry Curing of Seabass and Cod: Product Characterisation and Listeria monocytogenes Challenge Test.

Dry-Curing of Sea Bass and Cod: Process Characterisation and Listeria monocytogenes Challenge Test The seafood industry continuously seeks innovative and sustainable preservation strategies capable of improving product stability and safety while maintaining nutritional and sensory quality. Among the available technologies, dry curing has gained increasing attention as a mild preservation technique based on the combined effects of dehydration, salt diffusion, and controlled environmental conditions. In this study, sea bass (Dicentrarchus labrax) and cod (Gadus morhua) fillets were subjected to a 96-hour (h) dry-curing process using a patented cabinet specifically designed for fishery product transformation. The protocol included salting (48 h), dripping (4 h), drying (18 h), and aging (4 h) phases under controlled climatic conditions. Samples collected at different time points (T0, T48, T52, T70, T96) were analysed to evaluate physicochemical (pH, aw) and microbiological changes, including total mesophilic count, total psychrotrophic count, Enterobacteriaceae, and lactic acid bacteria (LAB). A challenge test was performed to assess the behaviour of Listeria monocytogenes during processing. Fish fillets were inoculated with adapted reference strains according to ISO 20976-1:2019 guidelines, reproducing contamination scenarios potentially occurring during handling operations, and pathogen dynamics were monitored throughout transformation. During processing, pH values remained stable in both species. Water activity progressively decreased in cod, showing statistically significant differences between T0 and T96, with values decreasing from 0,990 to 0,960. A greater reduction was observed in sea bass, where aw declined from 0,999 to 0,939 over the processing period. Microbiological analyses revealed dynamic changes in microbial populations. In sea bass, mesophilic and psychrotrophic bacterial counts initially decreased after salting, likely due to the combined effects of salt, temperature, and ventilation, before increasing toward the final stages of processing. LAB showed a similar pattern, whereas Enterobacteriaceae resulted mostly below the detection limit. In cod, mesophilic and psychrotrophic bacteria progressively increased throughout transformation, while Enterobacteriaceae and LAB were generally undetectable. Challenge test results showed an initial reduction of L. monocytogenes counts occurred in both species (ΔT48-T0 = −27.57% in sea bass; ΔT48-T0 = −30.06% in cod), suggesting an inhibitory effect of salting and environmental conditions. In the subsequent stages, L. monocytogenes counts showed stable trends in sea bass, with no statistically significant differences, whereas cod exhibited a moderate increase in L. monocytogenes counts from 3.55 to 4.45 log CFU/g (ΔT52-T0 = +25.35%), possibly related to the higher aw values observed in this species. Overall, the results indicate that dry curing contributed to limiting the growth of L. monocytogenes during the early stages of transformation; however, pathogen persistence throughout processing highlights the need for appropriate control measures. As dry-cured fishery products fall within the category of ready-to-eat foods capable of supporting the growth of L. monocytogenes under Regulation (EC) No 2073/2005, strict hygiene management and process validation are essential to ensure product safety.