Listeria monocytogenes Control Strategies Applied to Fresh and Cold-Smoked Salmon

Introduction:  Salmon products with high levels of Listeria monocytogenes represent a potential health threat for consumers and is a serious microbial challenge for the salmon industry. Hygienic processing is essential for Listeria control, but cannot ensure absence in salmon and salmon products. Therefore, the salmon industry has shown an increasing interest in methods with documented effects for elimination or reduction of Listeria, when applied directly on salmon and salmon products.

Purpose:  This investigation was undertaken to evaluate selected methods/technologies that are used in the industry, or are regarded to have potential for industrial use, for their effect and limitations on Listeria elimination or reduction on fresh and cold-smoked salmon.

Methods:  Salmon was contaminated with a 10-strain mixture of L. monocytogenes. Control strategies providing both Listeria kill and growth inhibiting effects were tested on fresh, raw salmon and cold-smoked salmon. Tested methods included UVC and pulsed UV light, H₂O₂-based desliming, and treatments using organic acid salts/fermentates and acidified sodium chlorite. Analyses determined Listeria reductions, growth inhibition, and investigated parameters affecting robust Listeria reductions under industry-relevant conditions.

Results:  Reductions of L. monocytogenes on salmon treated with UVC and pulsed UV light were similar (0.5-1.5 log), with higher effects on the skin of raw salmon and on fillets of smoked salmon compared to fresh salmon fillets. Organic acid salts and fermentates provided concentration and temperature dependent growth inhibition on cold-smoked salmon during storage. Growth inhibition, without killing Listeria, was also obtained on fresh salmon rinsed in fermentate solution. Limited effects were obtained using desliming and rinsing of fresh salmon in acidified sodium chlorite.

Significance:  The results provide the industry with knowledge-based information for selection of cost-effective, Listeria control strategies for raw and processed salmon.