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 fish products have not been prevalent.
The discovery of Listeria in seafood products has led to several recalls in recent years. In addition to possible consumer exposure, product recalls are a financial burden for those affected, and they may also lead to increased food waste.
Testing potential methods
“In our experiments, we’ve used several methods not yet approved by 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 either lead to a new method being approved – or not,” said senior researcher Tone Mari Rode, who leads the DeList project.
In the tests, brown trout are first exposed to Listeria bacteria and then dipped in various treatment baths to determine what can remove or reduce the bacteria in the fish fillet.
“We’ve used acetic acid, low pH, and antimicrobial – bacteria-inhibiting – substances. Nisin, 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 are combining different methods, such as high pressure and baths, with various additives.
“We compare the test fish with trout that hasn’t been dipped in Listeria to compare what bacteria-inhibiting methods do to color, texture, and microbiology – in other words, shelf life. The fish is also stored over time to check the effect the treatment has on the development of both quality and bacterial growth. Listeria can grow – even at refrigerator temperature. Even if there are only ten bacteria in a product, and these can be removed, that represents a significant potential gain,” said Rode.
Results will provide knowledge about decontamination methods and technologies that kill and inhibit Listeria in salmon and trout products.
Cleaning vital in Listeria fight
Nofima experts have also shared insight into how cleaning can prevent and combat Listeria in food production environments.
This report is based on a large international survey of food companies’ and their cleaning product suppliers’ experiences with Listeria. Three key points were the correct use of cleaning agents, the design of equipment and premises with cleaning in mind and documenting the impact of existing products.
There are increasingly strict requirements to tackle Listeria in food production. Due to environmental and safety requirements, some active substances currently used in cleaning products are expected to be phased out.
To avoid problems, it is recommended that food manufacturers implement a Listeria control plan that includes hygienic design, effective hygiene routines, a robust cleaning program, and a sampling program; ensure regular maintenance and upgrading of equipment; and quickly identify the source and take measures if Listeria is found in the production environment or products.
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