Estimating the maximum growth rate from microbial growth curves: definition is everything

We compared values of μmax obtained by applying the Gompertz, logistic and Baranyi-Roberts models to experimental data on the growth of Listeria monocytogenes and Listeria innocua using both absorbance and viable counts measurements of cell concentration. All three models fitted the experimental data well, however, the values of μmax obtained using the Gompertz and logistic models were similar to each other but substantially different from those predicted by the Baranyi-Roberts model. The latter growth model was used to derive a second estimate of μmax based on the slope at the inflection point of the growth curve function; this value was in closer agreement with those obtained using the Gompertz or logistic models. Conditions were identified when values of μmax based on different definitions would converge towards one another.