Modeling the effect of Croton blanchetianus Baill essential oil on pathogenic and spoilage bacteria.

This study aimed to evaluate and model the antimicrobial action of different concentrations of Croton blanchetianus essential oil (CBEO) on the behavior of six bacterial species in vitro. CBEO extraction was performed by hydrodistillation and characterized by CG-MS. CBEO solutions in culture media were tested at 0.90, 1.80, 2.71, and 4.51 mg of CBEO/mL, against foodborne bacteria: pathogenic bacteria (Staphylococcus aureus, Listeria monocytogenes and Salmonella Enteritidis at 35 °C), a non-pathogenic Escherichia coli (at 35 °C), and spoilage bacteria (Weissella viridescens and Leuconostoc mesenteroides at 30 °C). The CBEO major compounds were eucalyptol, α-pinene, sativene, E-caryophyllene, bicyclogermacrene, and spatulenol. Baranyi and Roberts (growth) and Weibull (inactivation) primary models, along with power and hyperbolic secondary models, were able to describe the data. CBEO inactivated L. monocytogenes, S. aureus, L. mesenteroides and W. viridescens at all applied concentrations. CBEO did not inactivate S. Enteritidis and E. coli, but their growth rates were reduced.

Modelling the inactivation, survival and growth of Salmonella enterica under osmotic stress considering inoculum phase and serotype.

AIMS: This study evaluated the behaviour of the Salmonella enterica serotypes in osmotically stressful BHI broth (0.940 ≤ aw  ≤ 0.960), assessing inoculum from two stages of the bacterial life cycle (exponential and stationary) and two temperatures (25°C and 35°C). METHODS AND RESULTS: Four S. enterica serotypes (Typhimurium, Enteritidis, Heidelberg and Minnesota) were grown in stressful BHI at 25°C. A mathematical model was proposed for describing the total microbial count as the sum of two subpopulations, inactivating and surviving-then-growing. When submitted to aw of 0.950 and 0.960, all strains showed a decreased count, followed by a period of unchanged count and then exponential growth (Phoenix Phenomenon). Strains inoculated at aw  = 0.940 and 0.945 showed inactivation kinetics only. Cells cultivated at 25°C and inoculated from the exponential phase were the most reactive to the osmotic stress, showing a higher initial population reduction and shorter adaptation period. The proposed model described the inactivation data and the Phoenix Phenomenon accurately. CONCLUSIONS: The results quantified the complex response of S. enterica to the osmotic environment in detail, depending on the inoculum characteristic and serotype evaluated. SIGNIFICANCE AND IMPACT OF STUDY: Quantifying these differences is truly relevant to food safety and improves risk analysis.