Snapshot 1: growth rate parameter of a psychrophilic organism

Snapshot 2: growth rate parameter of a mesophilic organism

Snapshot 3: growth rate parameter of a thermophilic organism

Snapshot 4: inactivation rate parameter of a vegetative bacterial cell

Snapshot 5: inactivation rate parameter of a heat resistant bacterial endospore

Snapshot 6: inactivation rate parameter of a heat resistant bacterial endospore where

Ratkowski’s original model was written in the form

, where

is the growth rate parameter (usually the isothermal growth curve’s slope at its inflection point),

is the temperature, and

is the temperature below which growth ceases [1, 2]. The model can also be written in the general form: if

, 0., else

, where

can but need not always be equal to 2 [2, 3].

In principle, the model can also be used for thermal inactivation, where

is the inactivation rate parameter and

is a temperature marking the onset of lethality [4].

This Demonstration provides a graphical representation of Ratkowski’s model in its original and expanded versions in the region around

, that is, before growth is turned into inactivation or vice versa. Choose between pure growth and inactivation with the setter bar. You can use sliders to vary temperature in

, and the magnitudes of

,

, and

. The plot of the corresponding

versus

relationship has a blue arrow marking

and a moving point on the curve. The numerical coordinates of the movable point, which are the values of

and corresponding

, are displayed above the plot.

When

, the model yields

versus

relationships that are reminiscent of those produced by the log-logistic model.

The purpose of this Demonstration is only to illustrate the Ratkowski model and its modifications, not to match any particular organism or process. Therefore, not all parameter combinations allowed by the controls represent realistic growth or inactivation scenarios.

[1] D. A. Ratkowski, J. Olley, T. A. McMeekin, and A. Ball, "Relationship between Temperature and Growth Rate of Bacterial Cultures,"

*Journal of Bacteriology*,

**149**(1), 1982 pp. 1–5.

[2] T. Ross, "Bĕlehrádek-Type Models,"

*Journal of Industrial Microbiology and Biotechnology*,

**12**(3–5), 1993 pp. 180–189.

doi:10.1007/BF01584188.

[3] L. Huang, C.-A. Hwang, and J. Phillips, "Evaluating the Effect of Temperature on Microbial Growth Rate—The Ratkowski and a Bĕlehrádek-Type Models,"

*Journal of Food Science*,

**76**(8), 2011 pp. M547–M557.

doi:10.1111/j.1750-3841.2011.02345.x.

[4] M. M. Gil, T. R. S. Brandão, and C. L. M. Silva, "A Modified Gompertz Model to Predict Microbial Inactivation under Time-Varying Temperature Conditions,"

*Journal of Food Engineering*,

**76**(1), 2006 pp. 89–94.

doi:10.1016/j.jfoodeng.2005.05.017.