Creating value
2013
nofima.no
12
Financed by:
The Research Council
of Norway
Partner:
KU Leuven University,
Belgium
Torstein Skåra places a sample in the steam chamber of the test rig. It is closed and steam is injected from above at given time intervals.
photo: Jan Thomas Rosnes © Nofima
Listeria monocytogenes is a pathogenic bacterium that
creates problems for the seafood industry by contami-
nating the surface of products with otherwise good
microbiological status. Chilled products with extended
shelf life, such as smoked fish or processed fish prod-
ucts, are particularly vulnerable as the bacteria grow at
refrigeration temperature.
“The main objective of my PhD project has there-
fore been to find a method that can eliminate possible
contamination by Listeria from the products just before
packing,” says Nofima Scientist Torstein Skåra.
Surface team pasteurisation:
A specially designed
test rig built at the University of Bristol was purchased
for the experiments. The Listeria bacteria are then elimi-
nated 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 sur-
faces of the products. He used spectroscopic technology
to determine the effect of the heat treatment on the
product. Models were used to compare steam pasteuri-
sation 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 find-
ings 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.
Rapid heating of the surface with steam at 100 °C can kill unwanted
bacteria on fish products.
Removing Listeria with steam
