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Title: Determination of 5-log reduction times for Escherichia coli O157:H7, Salmonella enterica, or Listeria monocytogenes in acidified foods with pH 3.5 or 3.8

item Breidt, Frederick
item KAY, KATHRYN - North Carolina State University
item COOK, JAMES - Non ARS Employee
item OSBORNE, JASON - North Carolina State University
item INGHAM, BARBARA - University Of Wisconsin
item ARRITT, FLETCHER - North Carolina State University

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2013
Publication Date: 7/1/2013
Publication URL:
Citation: Breidt, F., Kay, K., Cook, J., Osborne, J., Ingham, B., Arritt, F. 2013. Determination of 5-log reduction times for Escherichia coli O157:H7, Salmonella enterica, or Listeria monocytogenes in acidified foods with pH 3.5 or 3.8. Journal of Food Protection. 76(7):1245-1249.

Interpretive Summary: The safety of acidified foods, salad dressings, and related products depends on assuring the destruction of bacterial pathogens. This work shows the times and acid conditions needed to kill disease causing bacteria in acidic foods that are not heat processed. While these products are inherently safe due to the acid used in manufacture (typically vinegar), some disease causing bacteria are very acid resistant, and may be on ingredients, such as fresh produce. Depending on conditions of manufacture and storage, some disease causing bacteria such as Escherichia coli can survive for 1 month or more if the products if not properly treated. Our research defined the treatments necessary to assure these bacteria are killed during processing. We also present data showing that benzoate, a food preservative commonly used to prevent the growth of spoilage bacteria, can also be very effective in killing the disease causing bacteria. The data presented in this manuscript may be helpful for defining the critical controls needed for the safety of acidic foods, as required under the Food Safety Modernization Act.

Technical Abstract: A critical factor in ensuring the safety of acidified foods is the establishment of a thermal process that assures the destruction of acid-resistant vegetative pathogenic and spoilage bacteria. For acidified foods such as dressings and mayonnaises with pH values of 3.5 or higher, the high water phase acidity (acetic acid of 1.5 to 2.5% or higher) can contribute to lethality, but there is a lack of data showing how the use of common ingredients such as acetic acid and preservatives, alone or in combination, can result in a 5-log reduction for strains of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in the absence of a postpackaging pasteurization step. In this study, we determined the times needed at 10°C to achieve a 5-log reduction of E. coli O157:H7, S. enterica, and L. monocytogenes in pickling brines with a variety of acetic and benzoic acid combinations at pH 3.5 and 3.8. Evaluation of 15 different acid-pH combinations confirmed that strains of E. coli O157:H7 were significantly more acid resistant than strains of S. enterica and L. monocytogenes. Among the acid conditions tested, holding times of 4 days or less could achieve a 5-log reduction for vegetative pathogens at pH 3.5 with 2.5% acetic acid or at pH 3.8 with 2.5% acetic acid containing 0.1% benzoic acid. These data indicate the efficacy of benzoic acid for reducing the time necessary to achieve a 5-log reduction in target pathogens and may be useful for supporting process filings and the determination of critical controls for the manufacture of acidified foods.