Modeling the aerobic growth and decline of Staphylococcus aureus as affected by pH and potassium sorbate concentration

The effects of pH (5.0, 5.2, 5.4, 5.6, and 5.8) and concentration of potass ium sorbate (10.0 and 16.6 mM) at two water activity values (0.90 and 0.92) on the aerobic growth and decline of Staphylococcus aureus ATCC 6538P, 196 -E, and FDA-C243 were studied using brain-heart infusion broth. The inoculu m was approximately 4 to 5 log CFU/ml, and the incubation temperature was 3 0 degrees C. Samples were periodically enumerated on tryptic soy agar. The Gompertz model was used to obtain microbial growth parameters, specific gro wth rate was obtained as a derived parameter, and the inhibition index was calculated. A linear model was fitted in cases of bacteriostatic or bacteri cidal action of the treatment. The ATCC 6538P strain showed the highest res istance in the range of tested conditions. Microbial behavior was modeled c onsidering the main controlling factors, and a response surface methodology was used to determine the effects of undissociated acid concentration and pH. These results can be used to establish treatment conditions fbr microor ganism growth or inhibition.