A phenomenological model to infer the microbial growth: A case study for psychrotrophic pathogenic bacteria

The two-parameter (α and β) Schiraldi's model reliably fits growth curves of psychrotrophic pathogens and suggests a different description of the latency phase.

Data obtained at various temperatures and different starting cell densities for Aeromonas hydrophila, Listeria monocytogenes and Yersinia enterocolitica have been fitted with the Baranyi and Roberts' model and the new one. On average, the former showed higher standard error and R² values (0.140 and 0.991) than the Schiraldi's one (0.079 and 0.983). Around 15℃, the increase of temperature showed a milder effect on the growth rate than that expected. Y. enterocolitica showed a practically null duration of the lag phase, no matter the value of the starting density, whereas A. hydrophila and L. monocytogenes revealed slower onset trends.

Parameter β defines the number of cell duplications and appears independent on temperature, while (β/α)^1/2 is proportional to the maximum specific growth rate. The α^-1/2 versus temperature trend directly reflects the corresponding behaviour of the growth rate and does not require the use of Arrhenius plots.

Values of the parameters α and β, as well as the duration of the latency phase, allowed some considerations about the effect of storage temperature in terms of food safety, especially for psychrotrophic bacteria of concern.