29G-25 |
Survival of Esherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium in prepared mustards |
M. S. Rhee, S. Y. Lee, R. H. Dougherty, and D. H. KANG. Dept. of Food Science & Human Nutrition, Washington State Univ., PO Box 646376, Pullman, WA 99164-6376 The involvement of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium in outbreaks associated with the consumption of acidic foods has drawn attention to the acid adaptation response of these pathogens and its impact on resistance to environmental stresses, especially acids. Therefore, it is necessary to understand the combined effects of several factors in acidic foods on controlling foodborne pathogens. This study was undertaken to investigate the individual or combined effect of mustard flour and acetic acid for the inactivation of foodborne pathogens stored at 5 and 22°C. Samples of various concentrations were prepared by the addition of acetic acid (0, 0.5, or 1%) along with mustard flour (0, 10, or 20%) and 2 % sodium chloride (fixed). Acid-adapted three-strain mixtures of E. coli O157:H7, L. monocytogenes, or S. typhimurium strains (106-7 CFU/ml) were inoculated separately into prepared mustard samples stored at 5 and 22°C, and samples were assayed periodically. The order of bacterial resistance against prepared mustards at 5°C was S. typhimurium (1 d) < E. coli O157:H7 (3 d) < L. monocytogenes (9 d). Levels of foodborne pathogens were reduced much more rapidly at 22°C than at 5°C. There was no synergistic effect with regard to the killing of tested pathogens by the addition of 0.5% acetic acid to the mustard flour (10 or 20%). The reduction of tested pathogens among the combined treatments at the same storage day was generally differentiated as follows: control < mustard + 0.5% acetic acid < mustard alone < mustard + 1% acetic acid < acetic acid alone. The addition of small amounts of acetic acid (0.5%) to mustard can retard the reduction of foodborne pathogens. These antagonistic effects may be changed if mustard is used alone or in combination with >1% acetic acid.
Session 29G, Food Microbiology: General
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