How safe from Listeria monocytogenes are frozen ready-to-eat fish products, either cooked or smoked, when stored under refrigeration after purchasing?

Abstract This research aimed to access the incidence of Listeria sp. and L. monocytogenes in frozen ready-to-eat (RTE) fish products immediately after purchasing, and after refrigerated storage. Out of 72 kani-kama samples, 17 (23,6%) and 16 out of 48 samples (33,3%) of smoked salmon samples, tested positive for Listeria sp. by the traditional culture method, whereas 45,8% and 56.2% were positive by PCR, for kani-kama and smoked salmon samples, respectively. Applying qPCR, 21 samples of kani-kama out of 72 (29.2%) and 23 out of 48 samples of smoked and sliced salmon (47.9%) were positive for L. monocytogenes . Quantification was performed by culture to account only for viable cells, and confirmation was carried out via PCR and qPCR for Listeria sp. and L. monocytogenes , respectively. The average counts of L. monocytogenes did not exceed 2 Log CFU/g, both in kani-kama or smoked salmon. However, 15.3% of individual kani-kama samples and 14,6% of smoked salmon samples showed counts of up to 3.2 Log CFU/g, some even immediately after purchasing. Higher number of positive samples was observed during refrigerated storage compared to the number of samples analysed immediately after purchasing, indicating that refrigeration for a long time can pose an additional health threat. Unlike kani-kama, which is a heat-processed product, a higher background microbiota count was detected in smoked salmon. However, this background microbiota apparently did not influence the growth of Listeria spp.