title: Water Diffusion from a Bacterial Cell in Low-Moisture Foods.
abstract: We used a Fick's unsteady state diffusion equation to estimate the time required for a single spherical shaped bacterium (assuming Enterococcus faecium as the target microorganism) in low-moisture foods to equilibrate with the environment. We generated water sorption isotherms of freeze-dried E. faecium. The water activity of bacterial cells at given water content increased considerably as temperature increased from 20 to 80 °C, as observed in the sorption isotherms of bacterial cells. When the water vapor diffusion coefficient was assumed as between 10(-12) and 10(-10) m(2) /s for bacterial cells, the predicted equilibration times (teq ) ranged from 8.24×10(-4) to 8.24×10(-2) s. Considering a cell membrane barrier with a lower water diffusion coefficient (10(-15) m(2) /s) around the bacterial cell with a water diffusion coefficient of 10(-12) m(2) /s, the teq predicted using COMSOL Multiphysics program was 3.8×10(-1) s. This result suggests that a single bacterium equilibrates rapidly (within seconds) with change in environmental humidity and temperature.
authors: Dept. of Agricultural, Food and Nutritional Science, Univ. of Alberta, Edmonton, Alberta, Canada, T6G 2P5. syamalad@ualberta.ca.
authors: Roopesh M
authors: RM
authors: Syamaladevi
authors: Biological Systems Engineering Dept, Washington State Univ, P.O Box 646120, Pullman, Wash, 99164-6120, U.S.A. jtang@wsu.edu.
authors: Juming
authors: J
authors: Tang
authors: College of Food Science, South China Agricultural Univ, Tianhe, Guangzhou, 510642, P. R. China.
authors: QingPing
authors: Q
authors: Zhong
mesh_terms: D002462:Cell Membrane; D004058:Diffusion; D016984:Enterococcus faecium; D005516:Food Microbiology; D005612:Freeze Drying; D006801:Humans; D006813:Humidity; D013227:Steam; D013696:Temperature; D014867:Water / Q000502:physiology*
chemical_list: D013227:Steam; D014867:Water
keywords: Enterococcus faecium; low-moisture foods; mathematical modeling; sorption isotherm; water activity