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United States Department of Agriculture

Agricultural Research Service

Research Project: MICROBIAL MODELING AND BIOINFORMATICS FOR FOOD SAFETY AND SECURITY Title: Modelling Transfer of Listeria Monocytogenes During Slicing of "gravad" Salmon

Authors
item Aarnisalo, Kaarina - VTT TECH RES. FINLAND
item Sheen, Shiowshuh
item Raaska, Laura - VTT TECH RES. FINLAND
item Tamplin, Mark - UNIV. OF TASMANIA

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2007
Publication Date: August 15, 2007
Citation: Aarnisalo, K., Sheen, S., Raaska, L., Tamplin, M. 2007. Modelling transfer of listeria monocytogenes during slicing of "gravad" salmon. International Journal of Food Microbiology. 118(1):69-78.

Interpretive Summary: The transfer of an antibiotic (rifampicin) resistant mutant of Listeria monocytogenes strain F2365 from a contaminated (or inoculated) slicing blade to slices of 'gravad' salmon (Salmo salar), and from contaminated (or inoculated) salmon fillet to the slicing machine and subsequently to slices of uninoculated fillet was studied. The effect of slicing temperature (at 0 degree C, 10 degree C and room temperature), contamination (or inoculum) level [approximated 1000, 100000 and 100000000 Colony Forming Units (CFU) per blade], and attachment time of inoculum to blade (10 minute and 2.5 hour) were investigated and a predictive model of the transfer was developed. No statistically significant (p<0.05) differences in logarithmic reductions in the number of L. monocytogenes on slices were found between the different tests. Based on statistical parameters, an exponential model [y = a exp(-x/b)] fit the data most suitably for the different test conditions and could be used for predicting an expected number of L. monocytogenes on the salmon slices. The number of L. monocytogenes in slices from tests of transfer from inoculated blade to salmon was reduced by 95% (or 1.5-1.6 log CFU reduction) after slicing of 39 slices. A similar result was observed in tests of transfer from contaminated salmon to uninoculated blade and further to uninoculated salmon. The predictive models described herein can assist salmon processors and regulatory agencies in assessing possible cross-contamination from contaminated slicing machine to product and in designing risk management strategies.

Technical Abstract: Transfer of a rifampicin-resistant mutant of Listeria monocytogenes strain F2365 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 degree C, 10 degree 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 as an example, a predictive model of the transfer was produced. No statistically significant (p<0.05) differences in logarithmic reductions in the number of L. monocytogenes on slices were found between the different tests. Based on statistical parameters, an exponential model [y = a exp(-x/b)] fit the data most suitably for the different test conditions and could be used for predicting an expected number of L. monocytogenes on the salmon slices. The number of L. monocytogenes in 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 1.6 log CFU during slicing of 39 slices and 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. The predictive models described herein can assist salmon processors and regulatory agencies in assessing possible cross-contamination from contaminated slicing machine to product and in designing risk management strategies.

Last Modified: 10/21/2014
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