THE THE COMBINED EFFECT OF TEMPERATURE, pH AND LACTOSE CONCENTRATION ON THE GROWTH PROBABILITY OF LISTERIA INNOCUA
Keywords:Predictive microbiology, probabilistic models, growth/no growth, Listeria monocytogenes
Growth response data of Listeria innocua in broth were monitored at different combinations of temperature (4, 8 and 12 °C), pH (4.0, 4.5, 5.0, 5.5 and 6.0) and lactose concentration [0, 1, 2, 3, 4 and 5 (w/v %)] for 35 days. Especially low levels of temperature and pH were effective to prevent the growth of L. innocua whereas lactose concentration should be at least ≥ 4% at low temperature and pH values to obtain no growth response. Logistic regression model was developed to describe and further predict the growth boundaries of L. innocua under different combinations of the conditions. Goodness-of-fit indices and measures of predictive power such as percent concordant revealed that the fitted equation described the growth limits of L. innocua successfully. The proposed model could be also used to predict growth limits or probabilities of Listeria in whey at different temperature levels since pH and lactose concentration of whey is similar to the conditions tested and this was demonstrated for both sweet whey and acid whey. This study indicated that a quick estimate of growth probability of L. innocua is possible at different combinations of temperature, pH and lactose concentration.
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