Both primary and secondary models have been used in predictive microbiology. Primary models describe the changes in microbial population as a function of time, and secondary models describe the responses by parameters of primary models to changes in environmental conditions (Whiting, 1995). Arrhenius- and B ! elehr ! adek-type (square-root model) models are two major classes of secondary models that have been proposed to describe the effect of temperature on microbial growth.