Comparing predicting models for heat inactivation of Listeria monocytogenes and Pseudomonas aeruginosa at different pH.

Under the same experimental conditions it has been demonstrated that whereas survival curves of Listeria monocytogenes in the range of temperatures from 54 to 62 degrees C followed a first-order kinetic, those of Pseudomonas aeruginosa in the range of temperatures from 50 to 56 degrees C were not linear showing a shoulder followed by a linear region. The first order kinetic model did not describe survival curves of P. aeruginosa. A model based on the Weibull distribution (Log(10)(N(t)/N(0))=(1/-2.303)*(t/b)(n))) accurately described the inactivation kinetics of both microorganisms at the three pHs of 4, 5.5, 7.4 investigated. For both microorganisms, the b value depended on the treatment temperature and the pH of the treatment medium. Whereas for L. monocytogenes the n value was independent of the treatment conditions, for P. aeruginosa the n value depended on the pH of the treatment medium. The model based on the Weibull distribution was capable of accurately predicting the treatment time to inactivate five Log(10) cycles of both microorganisms at the three pHs investigated.