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Modelling transfer of Listeria monocytogenes during slicing of 'gravad' salmon


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Aarnisalo, K, Sheen, S, Raaska, L and Tamplin, ML 2007 , 'Modelling transfer of Listeria monocytogenes during slicing of 'gravad' salmon' , International Journal of Food Microbiology, vol. 118, no. 1 , pp. 69-78 , doi: 10.1016/j.ijfoodmicro.2007.06.017.

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Transfer of a rifampicin-resistant mutant of Listeria monocytogenes from an inoculated slicing blade to slices of 'gravad' salmon (Salmo salar), and from inoculated salmon fillet to the slicing machine and subsequently to slices of uninoculated fillet was studied. The effect of slicing temperature (0°C, 10°C and room temperature), inoculum level (approx. 3, 5 and 8 log CFU/blade), and attachment time of inoculum to blade (10 min and 2.5 h) were investigated and predictive models of the transfer were produced. The number of L. monocytogenes on slices from tests of transfer from inoculated blade (8.1-9.0 log CFU/blade or 5.9 log CFU/blade) to salmon was reduced on average 1.6 log CFU during slicing of 39 slices; the lowest reduction occurred at 0°C, being 1.3 log CFU. In tests of transfer from contaminated salmon (7.6 CFU/fillet) to uninoculated blade and further to uninoculated salmon, the reduction in number of L. monocytogenes in slices was 1.5 log CFU/39 slices. E.g. 5.3 CFU/g was transferred to second slice when the inoculum level was 8.4 log CFU/blade, but clearly (p<0.05) lower total numbers of L. monocytogenes were transferred to slices when the inoculum level was lower, the temperature was colder or the attachment time was longer. There was a progressive exponential reduction in the quantity of L. monocytogenes transferred and, based on statistical parameters, an exponential model (y=a*e(-x/b)) fit the data from different test conditions and was suitable for predicting an expected number of L. monocytogenes on the salmon slices. Based on the predicted values, the logarithmic reduction in numbers of L. monocytogenes in slices was highest at room temperature with an inoculum level of 8.4 log CFU/blade (attachment time 10 min); the other test conditions differed significantly from this (p<0.05). After slicing 156 slices (i.e. approximately three fillets), the numbers of L. monocytogenes in slices were predicted to be <1 log CFU/g in all conditions. The predictive models described herein can assist salmon processors and regulatory agencies in assessing cross-contamination from contaminated slicing machines to product and in designing risk management strategies

Item Type: Article
Authors/Creators:Aarnisalo, K and Sheen, S and Raaska, L and Tamplin, ML
Keywords: Listeria monocytogenes, 'gravad' salmon, transfer, predictive modelling
Journal or Publication Title: International Journal of Food Microbiology
ISSN: 0168-1605
DOI / ID Number: 10.1016/j.ijfoodmicro.2007.06.017
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