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Listeria in salmon killed by smoke treatment: Study

By Mike Stones , 23-Oct-2009

Smoking salmon at sufficiently high temperatures reduces the risk of Listeria monocytogenes, according to a new study from the Journal of Food Science, published by the Institute of Food Technologists.

Greater inactivation rates of Listeria monocytogenes occurred in samples processed at higher temperatures and in samples containing higher concentrations of salt and smoke compound, reported researchers from United States Department of Agriculture’s Agricultural Research Service (ARS) in Wyndmoor, Pennsylvania. They had focused on the survival of L. monocytogenes after treating with salt, smoke compound and temperature during the cold and hot-smoking of salmon.

Inactivation effect

The inactivation rate increased tenfold when the temperature increased by 5° C, indicating that smoking temperature is a main factor affecting the inactivation of the pathogen,” said the report. “In addition, salt and smoke compounds also contribute to the inactivation effect,” it added.

Smoked salmon is produced by salting, smoking and trimming or slicing the fish before n vacuum-packaging the product.

Able to grow at low temperatures, L. monocytogenes can contaminate fish if it is not processed and handled correctly. L. monocytogenes is a human pathogen that causes listeriosis and is particularly associated with refrigerated Ready-to-Eat foods.

Lead researcher Dr. Cheng-An Hwang said: “The data and model developed in this study can be used on select concentrations of salt and smoke compound, as well as smoking temperatures of 40° C to 55° C to minimize the presence of in smoked salmon and therefore, increasing its safety for consumers.”

Contamination

Manufacturers could use the results of the study, which also included research on the

survival of Listeria during storage, to reduce levels of contamination and further enhance the safety of smoked salmon, said the researchers.

Estimates of the prevalence of L. monocytogenes in cold-smoked salmon or smoked fish have been estimated at from 10% (Embarek, 1994) to 43% (Jorgensen and Huss, 1998). But the levels of contamination were generally low.

In one outbreak of listeriosis in Sweden, linked to L. monocytogenes, contamination of smoked salmon and smoked fish, sickened nine people and caused two deaths.

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