Abstract
Listeria monocytogenes may persist in food production environments and cause listeriosis. In Norway, a product of concern is the traditional and popular fermented fish product “rakfisk”, which is made from freshwater salmonid fish by mild-salting and brine maturation at low temperatures for several months. It is eaten without any heat treatment, and L. monocytogenes, therefore, poses a potential hazard. We investigated the effect of salt and temperature on the growth of L. monocytogenes in rakfisk during the 91 days of maturation. The amounts of organic acids produced during fermentation were too low to inhibit growth of L. monocytogenes. Temperature was clearly the most important parameter for controlling L. monocytogenes. At 7 °C, approximately 2 log growth was observed during the first 14 days of fermentation, and the level of L. monocytogenes thereafter remained constant. At 4 °C, only a little growth potential of the pathogen was recorded. We also investigated the effect of the anti-Listeria bacteriophage P100 on rakfisk with added L. monocytogenes. The phage was introduced to the L. monocytogenes-inoculated fish before fermentation, and an average of 0.9 log reduction was observed throughout the fermentation period. This is the first study of L. monocytogenes behavior in rakfisk and points to possible measures for increasing the product safety.
Highlights
Listeria monocytogenes is a facultatively anaerobic, Gram-positive bacterium, resistant to various harsh conditions, and found ubiquitously in the environment
We examined the effects of the bacteriophage Listex P100 on L. monocytogenes in brine during the rakfisk ripening process and on vacuum-packed rakfisk fillets
The process of rakfisk is essentially generally described bacterial fermentation in combination process of rakfisk production is generally described as a bacterial fermentation in combination with so-called “autolysis”, i.e., the activity of endogenous fish enzymes that degrade and transform proteins so-called i.e., the activityanalysis of endogenous fish samples enzymesindicated that degrade andprocess transform and fat of“autolysis”, the fish [12,13]
Summary
Listeria monocytogenes is a facultatively anaerobic, Gram-positive bacterium, resistant to various harsh conditions, and found ubiquitously in the environment. L. monocytogenes causes listeriosis, a relatively rare foodborne infection affecting mainly elderly and immunocompromised persons [1]. The bacterium is found in a range of foods including dairy products, meat and egg products, seafood, freshwater fish, vegetables, and other ready-to-eat (RTE) foods [1,2], and the main cause of listeriosis is consumption of food contaminated from sources in the food processing. Foods 2020, 9, 119 environments [3] or at the retail level [4,5]. Legislation regarding L. monocytogenes in RTE food products in different countries was summarized by Jami et al [6].
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