Modeling the inactivation kinetics of Bacillus subtilis spores by nonthermal plasmas

The inactivation performances of different nonthermal plasmas are often compared with each other in terms of their decimal reduction values, typically obtained by linearizing selected segments of their inactivation curves. However, this approach is subjective and can result in uncertainties in the prediction of this parameter. To overcome this, in this paper, the application of models capable of describing inactivation curves in their entirety is considered. The authors employ the Baranyi and Weibull models, both commonly used for microbial inactivation by heat. An empirical model based on a third-order polynomial to seek greater accuracy is further proposed. Using these three inactivation models, predictions of decimal reduction values for 11 plasma inactivation studies of Bacillus subtilis spores are obtained and compared with their reported values. Although the agreement obtained between these different approaches is generally fair, the current practice of segmented linearization is shown to be overly simplistic. A rigorous model is therefore critical to capture the essentially nonlinear character of plasma inactivation kinetics and hence allow for an objective comparison of the performances of similar biocidal nonthermal plasmas.