Kinetic Model to Describe L. monocytogenes Growth in Bologna Sausage Formulated with Low NaNO2 Concentration

Introduction: Meat industry produces processed meat products formulated with low concentration of NaNO₂ because of health concern about NaNO₂, but low concentration of NaNO₂ in processed meat products may allow Listeria monocytogenes growth on bologna sausage.  

Purpose: This study developed kinetic models to describe L. monocytogenes growth in bologna sausage formulated with low concentration of NaNO₂.

Methods: A mixture of L. monocytogenes strains NCCP10805, NCCP10808, NCCP10809, NCCP10810, and NCCP10943 was inoculated on bologna sausage formulated with NaNO₂ (0 and 10 ppm) and NaCl (1.0, 1.25 and 1.5%). The samples were then stored at 4°C (1440 h), 10°C (552 h) and 15°C (192 h) under aerobic and anaerobic conditions. L. monocytogenes cell counts were enumerated on PALCAM agar during storage. The modified Gompertz model was fitted to the L. monocytogenes growth data to calculate maximum specific growth rate (μ_max; log CFU/g/h) and lag phase duration (LPD; h). The temperature effect on μ_max and LPD were evaluated with the square root model and a polynomial model, respectively. Developed models were validated with observed data, and root mean square error (RMSE) was calculated.

Results: L. monocytogenes growth on bologna sausage was observed at 4 - 15°C at all concentrations of NaNO₂ and NaCl for both aerobic and anaerobic conditions (P < 0.05). Significant effect of NaNO₂ on μ_max and LPD values was not observed. However, the effect of NaNO₂ on μ_max and LPD increased when NaNO₂ was combined with NaCl. Validation result showed that RMSE was 0.330 - 1.768.

Significance: To lower NaNO₂ concentration in bologna sausage, NaCl should be combined with NaNO₂ to control L. monocytogenes, and the developed model should be useful in describing L. monocytogenes growth in low-NaNO₂ bologna sausage.