Probabilistic Models to Predict the Growth Initiation Time for Pseudomonas spp. in Processed Meats Formulated with NaCl and NaNO2

This study developed probabilistic models to determine the initiation time of growth of Pseudomonas spp. in combinations with $NaNO_2$ and NaCl concentrations during storage at different temperatures. The combination of 8 NaCl concentrations (0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, and 1.75%) and 9 $NaNO_2$ concentrations (0, 15, 30, 45, 60, 75, 90, 105, and 120 ppm) were prepared in a nutrient broth. The medium was placed in the wells of 96-well microtiter plates, followed by inoculation of a five-strain mixture of Pseudomonas in each well. All microtiter plates were incubated at 4, 7, 10, 12, and $15^{\circ}C$ for 528, 504, 504, 360 and 144 h, respectively. Growth (growth initiation; GI) or no growth was then determined by turbidity every 24 h. These growth response data were analyzed by a logistic regression to produce growth/no growth interface of Pseudomonas spp. and to calculate GI time. NaCl and $NaNO_2$ were significantly effective (p<0.05) on inhibiting Pseudomonas spp. growth when stored at $4-12^{\circ}C$. The developed model showed that at lower NaCl concentration, higher $NaNO_2$ level was required to inhibit Pseudomonas growth at $4-12^{\circ}C$. However, at $15^{\circ}C$, there was no significant effect of NaCl and $NaNO_2$. The model overestimated GI times by $58.2{\pm}17.5$ to $79.4{\pm}11%$. These results indicate that the probabilistic models developed in this study should be useful in calculating the GI times of Pseudomonas spp. in combination with NaCl and $NaNO_2$ concentrations, considering the over-prediction percentage.