Purpose: The objective of this study was to develop growth/no growth (G/NG) models to predict L. monocytogenes growth responses in processed meat products formulated with low concentrations of sodium nitrite and sodium chloride.
Methods: A five-strain mixture of L. monocytogenes was inoculated in NBYE (nutrient broth plus 0.6% yeast extract) supplemented with sodium chloride (0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, and 1.75%) and sodium nitrite (0, 15, 30, 45, 60, 75, 90, 105, 120, and 141 ppm). The inoculated samples were stored aerobically and anaerobically at 4, 7, 10, 12, and 15°C for up to 1,680 h. Growth (G; value of 1) or no growth (NG; value of 0) for each combination was determined by turbidity for each storage temperature. The growth response data were analyzed by a logistic regression to predict the growth probability of L. monocytogenes as a function of sodium nitrite and sodium chloride. To validate the model performance, the predicted growth response from developed G/NG models were compared to the observed growth responses from frankfurters.
Results: Although a single application of sodium nitrite or sodium chloride significantly (P < 0.05) suppressed L. monocytogenes growth at 4 - 15°C, the combination of sodium nitrite and sodium chloride more effectively (P < 0.05) inhibited L. monocytogenes growth than single application of sodium nitrite or sodium chloride under both aerobic and anaerobic storage condition. Validation of the developed G/NG models with frankfurters showed 92% of agreement between predicted and observed growth responses.
Significance: The probabilistic models developed should be useful in determining appropriate concentrations of sodium nitrite and sodium chloride at low concentrations to inhibit L. monocytogenes growth in processed meat products.