Investigation of and modeling the effects of nisin, different salts, storage temperature and time against listeria monocytogenes strains

In this thesis, the stress effects of different concentrations of nisin, NaCl, KCl and potassium sorbate on Listeria monocytogenes strains were investigated under incubation conditions at different temperatures. In the first stage of the study, MIC values and growth rates of the strains were determined and 3 of 29 L. monocytogenes strains were selected. Concentrations of 0-50-100-200-400 µg/mL and 0-1-2-3-4% were used to determine the growth boundaries of the strains at different nisin and NaCl concentrations, respectively. In the study performed with 3 replications, with initial cell densities of 3 log10 and 6 log10, the growth/no-growth status was determined by OD measurements during the incubation period at 4-20-37 °C for 2 months and a probability model was created. In the next stage of the study, the effects of 0-1-2-3-4% KCl and 0-0.05-0.1-0.15-0.2% C6H7KO2 concentrations at 6 log10 initial cell density were investigated for 3 strains and modeling was done in the same way. It has been determined that the models developed in this study with acceptable model performance could be useful in controlling the growth of L. monocytogenes and determining the growth possibilities. UHT milk and homemade meat water were used to demonstrate the validation of the studies in the food environment. In the study conducted with nisin concentrations of 25-75-150-250 µg/mL, at 6 log10 initial strain density in food media with the addition of 1.5% KCl or 0.125% C6H7KO2, with colony counts made once a week during incubation at 8 and 12 °C for 2 months, growth/no-growth data were obtained. Of the 48 combinations created for the validation study, accurate estimates could be obtained in 22 (46%) for milk and 35 (73%) for meat water. The findings, model development and validation results show that rapid and accurate estimation of the growth of Listeria can be made using the probability model.