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United States Department of Agriculture

Agricultural Research Service

Title: A Predictive Model for Growth and Inactivation of Listeria Monocytogenes in Ph-Modified Chicken Salad During Cold Storage

Authors
item Guentert, A - PURDUE UNIVERSITY
item Linton, R - PURDUE UNIVERSITY
item Mohtar, R - PURDUE UNIVERSITY
item Tamplin, Mark
item Luchansky, John
item Cousin, M - PURDUE UNIVERSITY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2003
Publication Date: August 10, 2003
Citation: Guentert, A.H., Linton, R.H., Mohtar, R.H., Tamplin, M.L., Luchansky, J.B., Cousin, M.A. 2003. A predictive model for growth and inactivation of listeria monocytogenes in ph-modified chicken salad during cold storage. International Association of Food Proection. Abstract # P166, p. 117.

Technical Abstract: Ready-to-eat (RTE) foods such as prepared deli salads may become contaminated with L. monocytogenes due to contaminated ingredients and/or post-process contamination. Combinations of preservation strategies can reduce the risk of contracting listeriosis from RTE foods. A conservative predictive model was developed to illustrate the growth and inactivation kinetics of L. monocytogenes when subjected to varied pH (4.0-5.2) during storage at 5.0º, 7.2º and 21.1ºC. Commercially produced pasteurised chicken salad was modified to pH 4.0, 4.6 and 5.2 by adding 2N acetic acid or 2M sodium acetate. Twenty-five gram samples of the modified salad were individually inoculated with ~1x106 cells/g using a mixture of L. monocytogenes (Scott A, LCDC 81-861, and F2365) and stored at the three temperatures for >112 days. Samples were enumerated with the FDA modified Most-Probable-Number (MPN) procedure. Log MPN was plotted against time and results were compared to estimates from the USDA Pathogen Modelling Program (version 6.1). Inactivation was seen at all pH levels and all temperatures. At 21.1ºC, a 6-log reduction was seen in 14 days at pH 4.0, 52 days at pH 4.6 and 38 days at pH 5.2. Inactivation began immediately at pH 4.0, and after a lag phase of 10-12 days, at pH 4.6 and 5.2. Inactivation rates were slower in cold storage, with decreases of 1.1 log (pH 5.2) and >3 log (pH 4.0 and 4.6) after 119 days. The predictive model specifically addresses interactions between pH and temperature and can be used to develop formulation and storage guidelines for protein-based salads.

Last Modified: 9/2/2014