In the present study, a detailed knowledge of the growth behaviour of Cronobacter sakazakii (858 CECT), at different temperatures, in Tryptic Soy Broth (TSB) and Reconstituted Powdered Infant Formula Milk (RPIFM), is condensed into mathematical models.

Growth kinetic data of C. sakazakii were obtained at four different temperatures: 4, 8, 25 and 37 ºC. The kinetic data were fitted to Baranyi and Gompertz primary models to determine initial density (N_o), lag time (λ), maximum growth rate (μmax) and maximum population density (N_f). The Gompertz equation provided the best fit for experimental data and was selected as the most suitable primary model to describe the C. sakazakii growth behaviour. The results obtained revealed that the lag phase length was affected by temperature, decreasing with increasing temperature ranging from 101.89 h (8 ºC) to 0.834 h (37 ºC) in RPIFM. At the same time, the maximum growth rate (μmax) was temperature-dependent, with values of 0.027 ((cfu/ml)/h) at 8 ºC, 0.384 ((cfu/ml)/h) at 25 ºC, and 0.924 ((cfu/ml)/h) at 37 ºC for RPIFM.

The present study contributes to support the good handling practices recom - mended by FAO/WHO after reconstitution of PIFM, and the requirement of thermal/ non-thermal treatments after reconstitution, previous to neonatal feeding, to ensure RPIFM microbiological safety.