Environmental factors, including temperature and nutrient composition, have considerable impact on the growth dynamic of each microbial species; moreover it is strongly dependent on the selected strain. Therefore, the aim of this study was to describe and analyse the growth dynamics of the strain Lactobacillus acidophilus NCFM (Howaru) by predictive microbiology tools. The intensity of Lb. acidophilus NCFM growth in MRS broth and in milk was significantly affected by the incubation temperature described by the Gibson’s model, from which the optimal temperature for the Lb. acidophilus growth of 40.5 °C in MRS broth and 40.1 °C in milk was calculated. These cardinal temperatures were verified with the CTMI model providing also other cardinal (minimal Tmin, maximal Tmax, and optimal Topt) values for Lb. acidophilus NCFM growth Topt=40.2 °C, Tmin=15.4 °C, Tmax=46.0 °C and Topt=40.3 °C, Tmin=14.3 °C, Tmax=46.6 °C in MRS broth and in milk, respectively.
Authors:A. Medvedova, M. Kocis-Koval, and L. Valik
Presence of pathogenic strains of Escherichia coli in foodstuffs may pose a health risk for a consumer. Therefore, knowledge on the effect of environmental factors on the growth ability of E. coli is of great importance. In this work, the effect of incubation temperature (6–46 °C) and the combined effect of temperature and water activity (0.991–0.930) on the growth dynamic of E. coli PSII were analysed. Based on the growth curves obtained, growth parameters were calculated by using the Baranyi D-model. Growth parameters were further analysed in secondary phase of predictive modelling. Using the CM model that describes the effect of combined factors, cardinal values (Tmin = 4.8 ± 0.4 °C, Topt = 41.1 ± 0.8 °C, Tmax = 48.3 ± 0.9 °C, awmin = 0.932 ± 0.001, and awopt = 0.997 ± 0.003) for the isolate were calculated. Under optimal conditions, the specific growth rate is µopt = 2.84 ± 0.08 h−1. The results obtained may contribute to the assessment of the risk associated with the possible E. coli presence in raw materials and to the search for preventive measures with defined degree of accuracy and reliability.