PO28 | LISTERIA MONOCYTOGENES BEHAVIOUR DURING 30 DAYS OF SHELF-LIFE IN DRY-CURED SEABASS AND COD FILLETS

Giulia Polizzi¹, Elena Zanato¹, Laura Prandini¹, Federica Savini¹, Alessandra De Cesare¹, Valentina Indio¹, Lia Bardasi², Lucia Buratti², Mattia Ramini², Andrea Serraino¹, Alessandro Seguino¹ | ¹Dip. di Scienze Mediche Veterinarie, Università di Bologna, Ozzano dell'Emilia (BO), Italy; ²Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia-Romagna, Bologna, Italy.

Aim. Among innovative preservation strategies in the fishery products industry, dry curing has emerged as a mild preservation technology based on the combined effects of salting, dehydration, and controlled environmental conditions, capable of improving product stability and safety while enhancing sensory quality. However, scientific information on the microbiological safety of dry-cured fishery products remains limited. The present study aimed to evaluate the shelf-life evolution and the behaviour of Listeria monocytogenes in dry-cured sea bass (Dicentrarchus labrax) and cod (Gadus morhua) during refrigerated storage.

Methods. Three independent batches of sea bass and cod, each comprising seven fillets per species, were subjected to a 96-h dry-curing process in a patented cabinet specifically designed for fishery product transformation. At the end of the process, the products were portioned, vacuum packaged and subjected to a 30-day shelf-life study. Samples were analysed at days 0, 7, 14, 22, and 30 for pH, water activity (a_w), total mesophilic and psychrotrophic bacterial counts, Enterobacteriaceae, lactic acid bacteria (LAB). In parallel, half of the fillets were experimentally inoculated with Listeria monocytogenes according to ISO 20976-1:2019 and EURL Lm (2021) guidelines to evaluate pathogen behaviour during refrigerated storage. L. monocytogenes enumeration was performed at the same sampling times.

Results. Throughout storage, pH remained substantially stable in both species, averaging 6.38 ± 0.21 in cod and 6.16 ± 0.11 in sea bass. Water activity increased during the first week of storage and subsequently stabilised, remaining above 0.94 in both products. Total mesophilic and psychrotrophic bacterial populations remained relatively stable throughout shelf life, with counts ranging between 7.3 and 8.9 log CFU/g. Enterobacteriaceae were generally below the detection limit in cod and progressively decreased in sea bass (Δ%_{T30 -T7} = −73.4%), whereas LAB showed an initial decline until T14 followed by growth, reaching increases of 1.36 and 2.16 log CFU/g in sea bass and cod, respectively, by the end of storage.
Challenge test results demonstrated that L. monocytogenes survived and grew throughout refrigerated storage in both species. In sea bass, counts increased from 3.14 to 5.04 log CFU/g, while cod showed a rise from 3.12 to 4.05 log CFU/g over the 30-day period. Similar trends were observed under both refrigeration scenarios, indicating limited influence of storage temperature on pathogen behaviour. The relatively high aw values maintained throughout storage likely contributed to the persistence and growth of L. monocytogenes.

Conclusions. Dry curing alone was insufficient to inhibit the growth of L. monocytogenes during refrigerated storage of vacuum-packaged sea bass and cod. 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, challenge testing, and process validation are essential to ensure product safety.