Model for the non-thermal inactivation of Listeria monocytogenes in a reduced oxygen environment
1995
Buchanan, R.L. | Golden, M.H.
The effect and interactions of temperature (4-42 degrees C), lactic acid concentration (0-2%) (pH 3.3-7.3), sodium chloride content (0.5-19.0%), and sodium nitrite concentration (0-200 microgram ml-1) on the survival of a three strain mixture of Listeria monocytogenes in an oxygen-limited environment was studied using sealed nitrogen-flushed flasks containing brain heart infusion broth. A total of 206 inactivation curves were generated, representing 157 different combinations of the four variables. The inactivation curves were fitted to both a linear and a non-linear primary model which were used to calculate the time to achieve a 4-D (99.99%) inactivation (t4D). Natural logarithmic transformed t4D values were subsequently used to generate secondary models of the four independent variables using response surface analysis. Qualitatively, t4D was inversely related to lactic acid concentration, temperature, and sodium chloride concentration with the effect of sodium nitrite being pH dependent. Quantitatively, the impact of the four variables was similar to that observed previously for aerobic conditions (Buchanan et al 1994). While sodium nitrite clearly accelerated the inactivation of L. monocytogenes in an acidic environment, comparison of the anaerobic model with an earlier aerobic model indicated that restricting oxygen levels did not enhance the activity of the curing agent. Once validated the models should provide a rapid means for estimating the survival of L. monocytogenes in acidified foods.
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