Norwegian scientists are working on a project investigating the separate or combined effect and suitability of different methods to reduce the presence of Listeria in salmon and trout.
The DeList project is funded by FHF, the Norwegian Seafood Research Fund, and will run until the end of January 2025.
Several recent studies have found Listeria monocytogenes in up to 10 percent of Norwegian salmon slaughterhouses and processing plants. Discoveries are often made in the environment and on equipment, but sometimes also on fish products.
The discovery of Listeria in seafood products has led to several recalls in recent years. In addition to the potential exposure of consumers, product recalls place a financial burden on those affected and can also lead to increased food waste.
Testing possible methods
“In our experiments we used several methods that have not yet been approved by the Norwegian authorities. That’s the nature of research. If you don’t try new methods, you won’t know what works and what doesn’t. We need to conduct experiments to get results that will lead to a new method being approved or not,” says senior researcher Tone Mari Rode, who leads the DeList project.
In the tests, brown trout are first exposed to Listeria bacteria and then dipped into various treatment baths to determine what can remove or reduce the bacteria in the fish fillet.
“We used acetic acid, a low pH value and antimicrobial bacteria-inhibiting substances. Nisin, which is approved in Norway for use in dairy products, is one of them,” said Rode.
Researchers are testing which measures can be implemented at a slaughterhouse. Listeria can be present on boats, in facilities and on slaughter equipment for farmed fish. They combine different methods, such as high pressure and bathing, with different additives.
“We compare the test fish with trout that has not been dipped in Listeria to compare what bacteria-inhibiting methods do to the color, texture and microbiology, in other words, the shelf life. The fish is also stored over time to monitor the effect the treatment has on the development of both quality and bacterial growth. Listeria can grow even at refrigerator temperatures. Even if there are only ten bacteria in a product, and they can be removed, that represents a significant potential profit,” said Rode.
The results will provide knowledge on decontamination methods and technologies that kill and inhibit Listeria in salmon and trout products.
Cleaning essential in Listeria battle
Nofima experts also shared insights into how cleaning can prevent and control Listeria in food production environments.
This report is based on a major international research of the experiences of food companies and their cleaning product suppliers with Listeria. Three key points were the correct use of cleaning products, designing equipment and buildings with cleaning in mind and documenting the impact of existing products.
Increasingly stricter requirements are being imposed on the control of Listeria in food production. Due to environmental and safety requirements, it is expected that some active ingredients currently used in cleaning products will be phased out.
To avoid problems, it is recommended that food manufacturers implement a Listeria control plan that includes sanitary design, effective hygiene routines, a robust cleaning program and a sampling program; ensure regular maintenance and modernization of equipment; and quickly identify the source and take action if Listeria is found in the production environment or products.
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