Microbiological status of smoked fish placed on the market in Poland

Abstract

Fish and fishery products are considered to be one of the most nutrient-rich dietary products. The nutritional value of fish depends on its freshness. The greatest role in fish spoilage is played by microbial decomposition. Smoking is one of the methods of fish preservation based on the action of temperature and the penetration into the tissue of preservative substances produced by burning wood. Almost all microorganisms except some pathogenic bacteria are destroyed in the smoking process; nevertheless, fish can be a source of some pathogenic microorganisms, i.e. Listeria monocytogenes, Salmonella spp., Staphylococcus spp., which are present as the result of cross-contamination at the stage after smoking, i.e. marketing and storage (4, 5, 8). Improper and unhygienic handling practices with the ready-to-eat RTE product are also the cause of an increase of the total microbiological contamination, which can be expressed by microbiological contamination indicators, i.e. total viable count (TVC), psychrophilic bacteria count (PBC), coliform count (EBC), total yeast and mould count (TYMC) and total staphylococci count (TSC). In the performed study five smoked fish species (redfish, mackerel, codfish, sprat and herring) were tested at the marketing stage. A total number of 50 (N = 50) samples was tested according to ISO standards. The potential foodborne bacteria in the tested samples were identified using a MALDI-TOF spectrometer combined with MALDI-Biotyper 3.0 software. In the performed study, the highest microbiology contamination TVC on the level 3.63 ± 0.15 log10 cfu/g and PBC on the level 3.04 ± 0.24 log10 cfu/g has been found in redfish muscle compared to herring, codfish, sprat and mackerel muscle. A significantly lower amount of 1.26 ± 0.12 log10 cfu/g yeast and moulds of was found in the muscle tissue of herring, compared to the other tested fish. The highest staphylococcal contamination of muscle tissue of redfish on the level 2.56 ± 0.15 log10 cfu/g and mackerel on the level 2.13 ± 0.15 log10 cfu/g was found. MALDI-TOF identification of isolated bacteria not confirmed the presence of Salmonella spp., Listeria monocytogenes and pathogenic Staphylococci and confirmed the presence of E. coli in tested redfish.