Sammendrag
Cold-smoked salmon are ready-to-eat products that may support the growth of pathogenic
Listeria monocytogenes during their long shelf-life. Consumption of such contaminated products can
cause fatal listeriosis infections. Another challenge and potential risk associated with CS salmon
is their high levels of sodium salt. Excess dietary intake is associated with serious health complications.
In the present study, anti-listerial bacteriocin (nisin), P100 bacteriophages (Phageguard L,
PGL) and fermentates (Verdad N6, P-NDV) were evaluated as commercial bio-preservation strategies
for increased control of L. monocytogenes in standard (with NaCl) and sodium-reduced (NaCl
partially replaced with KCl) CS salmon. Treatments of CS salmon with nisin (1 ppm) and PGL
(5 x 107 pfu/cm2) separately yielded significant initial reductions in L. monocytogenes (up to 0.7 log)
compared to untreated samples. Enhanced additive reductions were achieved through the combined
treatments of nisin and PGL. Fermentates in the CS salmon inhibited the growth of Listeria but did
not lead to its eradication. The lowest levels of L. monocytogenes during storage were observed in
nisin- and PGL-treated CS salmon containing preservative fermentates and stored at 4 C, while
enhanced growth was observed during storage at an abusive temperature of 8 C. Evaluation of
industry-processed standard and sodium-replaced CS salmon confirmed significant effects with up
to 1.7 log reductions in L. monocytogenes levels after 34 days of storage of PGL- and nisin-treated
CS salmon-containing fermentates. No differences in total aerobic plate counts were observed between
treated (PGL and nisin) or non-treated standard and sodium-reduced CS salmon at the end of
storage. The microbiota was dominated by Photobacterium, but with a shift showing dominance of
Lactococcus spp. and Vagococcus spp. in fermentate-containing samples. Similar and robust reductions
in L. monocytogenes can be achieved in both standard and sodium-replaced CS salmon using the
bio-preservation strategies of nisin, PGL and fermentates under various and relevant processing and
storage conditions.
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