Modeling growth rates as a function of temperature: model performance evaluation with focus on the suboptimal temperature range.

Secondary models, describing the microbial growth rate as a function of temperature, are evaluated with focus on model performance in the suboptimal temperature region. Escherichia coli K12 MG1655 is considered as the case study. A large set of square root of μ(max)(T)-estimates is fitted with (1) the cardinal temperature model with inflection (CTMI, Rosso et al., 1993), (2) the square root model (SQRT, Ratkowsky et al., 1983), and (3) the CTMI adapted to describe the particular behavior of Listeria at suboptimal temperatures (aCTMI, Le Marc et al., 2002). Compared to the CTMI and the SQRT, a more accurate description of the μ(max)(T)-relation is obtained with the aCTMI, certainly at temperatures below 30 °C. Also, the T(min) estimate is more realistic, i.e., ≈6 °C, compared to 8-8.5 °C for the CTMI and SQRT. Use of the aCTMI improved square root of μ(max)(T)-data description which points at the existence of two phases in the suboptimal temperature region of E. coli K12. The alternation of the square root of μ(max)(T) is most likely related to the cold shock response. These results reveal a possible shortcoming of the model structure of commonly used secondary models describing the temperature effect on the microbial growth rate.