Biopreservation: Control of Listeria monocytogenes Growth in Hot and Cold Smoked Salmon by Carnobacterium maltaromaticum CB1

Introduction: Recent outbreaks of Listeria monocytogenes in Canada and the US have captured significant attention by media and public to the risks of consuming minimally processed ready-to-eat foods. The risks associated with the consumption of L. monocytogenes in post-process contaminated smoked salmon are increased by their intrinsic properties, high water activity, pH, and salt, and minimal smoking, favoring the growth of L. monocytogenes. Health authorities require that manufacturers must validate no more than 0.5 log growth of L. monocytogenes over the product’s shelf-life.

Purpose: To determine if the application of a live bioprotective bacterium Carnobacterium maltaromaticum CB1 inhibits the growth of L. monocytogenes when applied to the surface of hot or cold smoked salmon.

Methods: Hot and cold smoked salmon was obtained from a commercial manufacturer and shipped on ice to the testing facility. A four-strain cocktail of biocompatible L. monocytogenes was used to inoculate the salmon surface at approximately 10³ CFU/g. The product was additionally inoculated with the bioprotective culture C. maltaromaticum CB1 at 10⁴ CFU/g. Product was vacuum packaged and stored at 4 °C for 28 days. Samples were enumerated every 3 or 4 days for total plate counts, L.  monocytogenes, and Carnobacterium spp., by plating onto the surface of Plate Count, PALCAM,  and Cresol red Thallium acetate Sucrose Inulin agars, respectively.

Results: C. maltaromaticum CB1 inhibited the growth of the cocktail of L. monocytogenes on hot and on cold smoked salmon for at least 7 days compared to control product. C. maltaromaticum CB1 grew well on the hot smoked salmon, but minimally on the cold smoked product. The slow growth of C. maltaromaticum CB1on the cold smoked salmon did not suppress its ability to control the growth of the cocktail of L. monocytogenes. 

Significance: The bioprotective culture C. maltaromaticum can extend the commercial shelf life of both hot and cold smoked salmon when growth of L. monocytogenes by 0.5 logs is used as the measure of shelf life.