ARS | Publication request: Viability of a multi-strain mixture of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 inoculated into the batter or onto the surface of a soudjouk-style fermented semi-dry sausage

Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 27, 2008
Publication Date: July 1, 2008
Citation: Porto Fett, A.C., Hwang, C., Call, J.E., Juneja, V.K., Ingham, S.C., Ingham, B.H., Luchansky, J.B. 2008. Viability of a multi-strain mixture of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 inoculated into the batter or onto the surface of a soudjouk-style fermented semi-dry sausage. Food Microbiology. 25:793-801.

Interpretive Summary: In recent years, there has been an increase in demand for ethnic/specialty sausages in the United States, primarily as a result of an increase in various immigrant populations; however there is a little information about the safety of these products. The presence of food borne pathogens in sausages is strictly regulated in the United States, and the United States Department of Agriculture/ Food Safety and Inspection Service requires ready-to-eat meat manufacturers to validate that their processes can control these bacteria in this category of food. Thus, in this study we evaluated the viability of L. monocytogenes, S. typhimurium, and E. coli O157:H7 inoculated either into the batter prior to stuffing or onto the surface of slices of Turkish soudjouk-style sausage stored at different temperatures. Fermentation to pH 4.8 or pH 5.2 and drying decreased pathogen levels by 10 to 100,0000 cells per gram of soudjouk sausage. When the surface of the sausages were contaminated pathogens numbers decreased by 10,000 cells after about 24 to 40 days, 12 to 26, 3.5 to 5.5, and 1 to 5.5 days after storage at 4, 10, 21, or 30 degree Celsius, respectively. Our results showed that fermentation to pH 4.8 and storage at greater than 21 degree Celsius was the most effective process/treatment for reducing the numbers of all three pathogens in soudjouk sausage. We also showed that slices of soudjouk sausage do not provide a favorable environment for outgrowth/survival of these pathogens.

Technical Abstract: Multi-strain mixtures of Listeria monocytogenes, Salmonella typhimurium, or Escherichia coli O157:H7 were separately inoculated either into soudjouk batter or onto the surface of slices of commercial soudjouk to levels of ca. 6.0 log10 CFU per gram or slice, respectively. After fermentation and drying of experimental sausage or after slicing of the commercial product, the soudjouk was packaged, vacuum-sealed, and stored at 4, 10, 21 or 30 degrees Celsius for up 90 days. Fermentation and drying alone reduced the numbers of L. monocytogenes by 0.07 and 0.74 log10 CFU/g for sausages fermented to pH 5.2 and pH 4.8, respectively, whereas the numbers of S. typhimurium and E. coli O157:H7 were reduced by 1.65 and 3.63 log10 CFU/g, and 0.03 and 1.11 log10 CFU/g, respectively. When sausages fermented to pH 5.2 or pH 4.8 were stored at 4, 10 or 21 degree Celsius for up 30 days, the numbers of L. monocytogenes, S. typhimurium, and E. coli O157:H7 decreased by an additional 0.08 to 1.80 log10 CFU/g, 0.08 to 3.83 log10 CFU/g, and 0.68 to 3.17 log10 CFU/g, respectively. Storage of commercially-manufactured soudjouk inoculated with L. monocytogenes, S. typhimurium, and E. coli O157:H7 at 4 or 10 degree Celsius, generated average lethality values (L-values; time in days to achieve a 1 log reduction in cell numbers) of 10.1, 7.6, and 5.9 days and 6.4, 4.3, and 2.9 days, respectively. However, when commercially-manufactured soudjouk was stored at 21 or 30 degree Celsius, the average L-values were ca. 1.4, 0.9, and 1.6, and 0.9, 1.4, and 0.25 days, respectively. The corresponding z-values for L. monocytogenes, S. typhimurium, and E. coli O157:H7 were about 22.6, 30.7, and 20.1 degree Celsius, respectively. These data reveal that fermentation to pH 4.8 and storage at greater than 21 degree Celsius was the most effective process/treatment for reducing the numbers of all three pathogens (about 2.5 to 5.25 log10 CFU/g). In addition, regardless of pH or storage temperature, slices of soudjouk-style sausage do not provide a favorable environment for outgrowth/survival of L. monocytogenes, S. typhimurium, or E. coli O157:H7.