Submitted by: Dr. Amy Simonne, Assistant Professor, Food Safety and Quality
Listeriosis gained its fame after the first reported outbreak associated with coleslaw in Canada in 1981. The bacterium Listeria monocytogenes, which is widespread in the environment, causes Listeriosis. The pH range for the growth of L. monocytogenes was thought to be 5.6-9.6, but new research results show that the organism can grow in laboratory media at a pH as low as 4.42. New research results further revealed that L. monocytogenes can survive and grow in refrigerated foods with pH values of approximately 4.0-5.0 and salt concentrations of 3-4%; thus home-fermented dill pickles fit this description .
Dill pickles by definition are fermented products of fresh cucumbers where the starter culture consists of the normal mixed surface flora of the cucumber surface. Cucumbers are one of the most commonly pickled foods in the US.
Home-fermented, refrigerator dill, cucumber pickles are the product of lactic acid fermentation. They are made by immersing the pickling cucumbers in brine solution and seasonings. Following this, the product typically ferments at room temperature for one week. The pickles are then stored in the refrigerator during the consumption period.
Since L. monocytogenes is widespread in the environment, contamination of this product with the organism can potentially cause serious problems because consumers do not normally heat the dill pickles prior to consumption. Newly published research by a team at the University of Georgia revealed that home-prepared dill pickles inoculated with L. monocytogenes tested presumptively positive for the organism for up to 49 days (in the internal tissue) and up to 91 days on the surface of the pickles with salt concentrations of 1.3, 3.8 or 7.6%.
Methodology
The researchers examined the fate of L. monocytogenes on the surface and in the interior of cucumbers and in brines of different salt concentrations (1.3, 3.8 and 7.6%) during a typical process of making homemade dill pickles. They measured the pH, salt (NaCl) and titratible acidity percentage, and the total population of Listeria, and other microorganisms of pickles left at room temperature storage at 2, 4, and 7 days (the fermentation period). Once the fermentation process was complete, they monitored the aforementioned parameters weekly during refrigerated storage.
Major findings:
Some of the inoculated L. monocytogenes cells in the treatment with the highest salt concentration of 7.6% remained viable.
Take home message:
Past recommendations for this type of product stated that consumption of refrigerator dill pickles, would be typically considered safe anytime after 3 days of refrigerated storage. However, from this study because L. monocytogenes may still be viable this point, there is a food safety risk.
This study recommended that home-prepared dill pickles of this type should not be distributed.
To identify at-risk population for Listeriosis, read the Research News You Can Use Summer 2005 at http://fycs.ifas.ufl.edu/newsletters/rnycufall05.pdf
References:
Listeriosis gained its fame after the first reported outbreak associated with coleslaw in Canada in 1981. The bacterium Listeria monocytogenes, which is widespread in the environment, causes Listeriosis. The pH range for the growth of L. monocytogenes was thought to be 5.6-9.6, but new research results show that the organism can grow in laboratory media at a pH as low as 4.42. New research results further revealed that L. monocytogenes can survive and grow in refrigerated foods with pH values of approximately 4.0-5.0 and salt concentrations of 3-4%; thus home-fermented dill pickles fit this description .
Dill pickles by definition are fermented products of fresh cucumbers where the starter culture consists of the normal mixed surface flora of the cucumber surface. Cucumbers are one of the most commonly pickled foods in the US.
Home-fermented, refrigerator dill, cucumber pickles are the product of lactic acid fermentation. They are made by immersing the pickling cucumbers in brine solution and seasonings. Following this, the product typically ferments at room temperature for one week. The pickles are then stored in the refrigerator during the consumption period.
Since L. monocytogenes is widespread in the environment, contamination of this product with the organism can potentially cause serious problems because consumers do not normally heat the dill pickles prior to consumption. Newly published research by a team at the University of Georgia revealed that home-prepared dill pickles inoculated with L. monocytogenes tested presumptively positive for the organism for up to 49 days (in the internal tissue) and up to 91 days on the surface of the pickles with salt concentrations of 1.3, 3.8 or 7.6%.
Methodology
The researchers examined the fate of L. monocytogenes on the surface and in the interior of cucumbers and in brines of different salt concentrations (1.3, 3.8 and 7.6%) during a typical process of making homemade dill pickles. They measured the pH, salt (NaCl) and titratible acidity percentage, and the total population of Listeria, and other microorganisms of pickles left at room temperature storage at 2, 4, and 7 days (the fermentation period). Once the fermentation process was complete, they monitored the aforementioned parameters weekly during refrigerated storage.
Major findings:
Some of the inoculated L. monocytogenes cells in the treatment with the highest salt concentration of 7.6% remained viable.
Take home message:
Past recommendations for this type of product stated that consumption of refrigerator dill pickles, would be typically considered safe anytime after 3 days of refrigerated storage. However, from this study because L. monocytogenes may still be viable this point, there is a food safety risk.
This study recommended that home-prepared dill pickles of this type should not be distributed.
To identify at-risk population for Listeriosis, read the Research News You Can Use Summer 2005 at http://fycs.ifas.ufl.edu/newsletters/rnycufall05.pdf
References:
Schlech, W. I., P. M. Lavigne, R. A. Bortolussi, A.C. Allen, E.V. Haldane, A.J. Won, A.W. Hightower, S.E. Johnson, S.H. King, E.S. Nicholles, and C. V. Broome. 1983. Epidemic listeriosis-evidence for transmission by food. N.Engl.J. Med. 308:203-206.
Swaminathan, B. 2001. Listeria monocytogenes. In Food Microbiology Fundamentals and Frontiers, 2nd ed. Eds. M.P. Doyle, L.R. Beuchat and T.J. Montville. ASM Press.
Kim, J.K., E.M. D’SA, M.A. Harrison, J.A. Harrison, and E. L. Andress. 2005. Listeria monocytogenes survival in refrigerator dill pickles. J. Food Prot. 68(11):2005, 2356-2361.
