title: Inactivation rates of Cronobacter spp. and selected other bacterial strains in powdered infant formulae stored at different temperatures.
abstract: The aim of this study was to determine the survival of two strains of Cronobacter (Enterobacter sakazakii) and six other bacterial strains inoculated into dry powdered infant formula (PIF) stored for 22 weeks at several temperatures between 7 and 42 degrees C. The experimental setup involved a relatively high initial concentration of bacteria, around 10(4) CFU/g of powder, and enumeration of survivors with a minimum detection level of 100 CFU/g. For all strains tested, it was found that the number of bacterial cells decreased faster with increasing temperature. Cronobacter spp. cells generally survived better at high temperatures (37 and 42 degrees C) than the other bacteria, while such a difference in survival was not apparent at other temperatures. To describe the effect of temperature on survival, both the Weibull distribution model and the log-linear model were tested. At 22 degrees C, decline rates of 0.011 and 0.008 log units per day were found for Cronobacter sakazakii ATCC 29544 and Cronobacter strain MC10, respectively. Assuming a linear relationship between log-transformed D-values and temperature, z-values estimated for C. sakazakii ATCC 29544 and Cronobacter MC10 were 13.3 and 23.5 degrees C, respectively. Such differences found in resistance among Cronobacter spp. would be relevant to consider when establishing quantitative risk assessments on consumer risks related to PIF.
authors.affiliation: Wageningen University, Laboratory of Food Microbiology, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: M C
authors.initials: MC
authors.lastname: Kandhai
authors.forename: M W
authors.initials: MW
authors.lastname: Reij
authors.forename: M
authors.initials: M
authors.lastname: van Schothorst
authors.forename: L G M
authors.initials: LG
authors.lastname: Gorris
authors.forename: M H
authors.initials: MH
authors.lastname: Zwietering
mesh_terms: D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D044083:Cronobacter sakazakii / Q000254:growth & development*; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D006801:Humans; D007223:Infant; D007225:Infant Food / Q000382:microbiology*; D041943:Infant Formula; D007231:Infant, Newborn; D018570:Risk Assessment; D013696:Temperature