Project Year 2013

Removing Listeria with steam

Rapid heating of the surface with steam at 100 °C can kill unwanted bacteria on fish products.

Listeria monocytogenes is a pathogenic bacterium that creates problems for the seafood industry by contaminating
the surface of products with otherwise good microbiological status. Chilled products with extended shelf life, such as smoked fish or processed fish products, are particularly vulnerable as the bacteria grow at refrigeration

“The main objective of my PhD project has therefore been to find a method that can eliminate possible contamination by Listeria from the products just before packing,” says Nofima Scientist Torstein Skåra.

SURFACE STEAM PASTEURISATION: A specially designed test rig built at the University of Bristol was purchased for the experiments. The Listeria bacteria are then eliminated using steam pasteurisation for a few seconds. The unique feature of surface steam pasteurisation is that it only affects the outermost part of the surface and, consequently, has a minimal impact on appearance or nutritional status.

Skåra performed a number of systematic experiments with various contamination levels of bacteria. This made it possible to quantify steam killing of Listeria on the surfaces of the products. He used spectroscopic technology to determine the effect of the heat treatment on the product. Models were used to compare steam pasteurisation with water bath treatment.

IMPROVED FOOD SAFETY WITH CORRECT USE: Skåra has studied the choice of various model organisms and compared the growth of Listeria monocytogenes strains isolated from the fish processing industry. These findings are important when using mathematical models to see how various organisms grow and how quickly they die. This work resulted in a new method for determining how efficiently steam kills Listeria.

“With correct use of this technology, the food safety of seafood products with extended shelf life may be improved considerably,” says Skåra.

KU Leuven University, Belgium

The Research Council of Norway

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