99D-7 |
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P. N. Skandamis1, Y. Yoon1, J. D. Stopforth1, P. A. Kendall2, and J. N. SOFOS1. (1) Dept. of Animal Sciences, Colorado State Univ., 1171 Campus Delivery, Fort Collins, CO 80523-1171, (2) Dept. of Food Science & Human Nutrition, Colorado State Univ., 1571 Campus Delivery, Fort Collins, CO 80523-1571 Literature data are available for the effect of single or double sublethal simultaneous stresses on responses of pathogens to subsequent lethal stresses. However, there is lack of information on whether there is a difference in pathogen resistance when exposed to more than one stresses, sequentially or simultaneously. The objective of this study was to evaluate the sequential or simultaneous application of osmotic, acidic and temperature shock on the heat and acid tolerance of Listeria monocytogenes. Stationary phase cells of a 10-strain composite of L. monocytogenes grown in tryptic soy broth with 0.6% yeast extract (TSBYE) were exposed to the following shocks: 10% NaCl for 1.5 h; pH 5.0 for 1.0 h or 1.5 h; temperature (T; 46°C) for 0.5 or 1.5 h; as well as to combinations of two or three of these stresses sequentially or simultaneously. The heat and acid tolerance of L. monocytogenes was then assessed in TSBYE at 52, 57 and 63°C and at pH 3.5, respectively. No cross-protection was evident at 52 and 63°C, while at 57°C there were more survivors than the control in decreasing order: pH-T > NaCl > NaCl-T=NaCl-pH > pH=T (0.5 or 1.5 h)=NaCl-pH-T. Survivors in cultures exposed to stresses sequentially or simultaneously were similar except for the simultaneous application of pH and T shock (1.5 h), which increased resistance compared to sequential exposure to these stresses. The heat (57°C) and acid tolerance of L. monocytogenes were enhanced by the same stresses; with the exception of pH (for 1.0 h or 1.5 h) and the sequential application of NaCl-pH-T which increased acid more that heat resistance. The results suggest that the combination and not necessarily the sequence or duration of stress is more crucial for the adaptive response of L. monocytogenes to heat and acid. Therefore, the results may have implications for the potential of L. monocytogenes contamination surviving mild heating, especially in products of reduced aw and pH.
Session 99D, Food Microbiology: General
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