Reduction and inhibition of Listeria monocytogenes in cold-smoked salmon by Verdad N6, a buffered vinegar fermentate, and UV-C treatments

Abstract

Contamination, survival and growth of Listeria monocytogenes in cold-smoked salmon represent serious health hazards to consumers and major challenges for salmon processors. Verdad N6, a commercially available buffered vinegar, was evaluated as an ingredient in cold-smoked salmon with regard to anti-listerial effects under processing and storage, sensory quality and consumer preference, effects on background microbiota and yield during production. Cold-smoked salmon with Verdad N6 added in the dry-salting process was produced. Salmon fillets were surface contaminated with a mix of L. monocytogenes. Levels of L. monocytogenes were determined during vacuum pack refrigerated storage for 29 days. The use of Verdad N6 resulted in increased lag times and reduced growth rates of L. monocytogenes. The inhibitory effects were dependent on Verdad N6 levels (0-2%), storage time and temperature (4 or 8 °C), type of contamination (between slices or on non-sliced salmon) and degree of smoking. The presence of dextrose (1%) in the recipe had no significant effects on L. monocytogenes levels after storage. On sliced salmon, complete growth inhibition at 4 °C storage could be obtained using 1% Verdad N6 compared to a 3 log increase in L. monocytogenes counts in control salmon. At abuse temperatures (8 °C), corresponding L. monocytogenes levels increased <2 log and 5-6 log during 29 days storage. On non-sliced salmon, 1% Verdad N6 provided complete growth reductions at 4 and 8 °C storage while L. monocytogenes in control salmon increased 2.3 and 4.6 log, respectively, in the same period. The use of Verdad N6 in combination with bactericidal UV-C treatments (fluence 50 mJ/cm²) provided an initial 0.8 log reduction and complete L. monocytogenes growth inhibition on subsequent storage at 4 and 8 °C. Salmon with Verdad N6 showed reduced levels of total counts during storage and a shift in the dominating bacteria with reduced and increased relative levels of Photobacterium and lactic acid bacteria, respectively. A consumer test showed no consistent differences in liking of salmon with and without Verdad N6. In summary, Verdad N6 is an option for the production of high quality cold-smoked salmon with enhanced food safety through its robust listeriostatic effects. The application of Verdad N6 in combination with listericidal UV-C light treatment can further reduce the listeria-risks of this ready-to-eat food product category.

Keywords: Cold-smoked salmon; Food safety; Listeria monocytogenes; Organic acid salts; UV-light.