Thermal death time measurement using thin flexible sleeves: a new experimental approach for determining microbial...

The thermal death time kinetics of Salmonella Enteritidis (SE) was measured in buffer, egg yolk, and albumen using thin layer plastic sleeves. The sleeves allowed for the loading and sampling of liquids of high or unusual viscosity, as in the case of yolk and albumen, and accepted relatively large volumes (2 to 3 ml) of fluid. The sleeves maintained the volume of the fluid in a thin layer and could be easily handled for heat exposure. The thin layer maintained one-dimensional heat transfer and minimized temperature gradients, thus preventing parts of the fluid from experiencing different heating rates. A representative strain of SE associated with an egg-based salmonellosis outbreak was used in this study. The D- and z-values of the chosen strain, H7037, were measured in buffer, yolk, and albumen. In buffer, SE had the following mean (±standard deviation) D-values: D(55°C) = 3.51 ± 0.30 min, D(57°C) = 1.75 ± 0.13 min, and D(60°C) = 0.25 ± 0.06 min. In yolk, D(58°C) = 0.90 ± 0.05, D(60°C) = 0.26 ± 0.03, and D(62°C) = 0.20 ± 0.02. In albumen, D(55°C) = 1.26 ± 0.31, D(56°C) = 0.68 ± 0.10, and D(57°C) = 0.44 ± 0.04. The z-values for SE calculated from these D-values were 4.29 ± 0.39°C in buffer, 6.12 ± 0.26°C in yolk, and 4.63 ± 1.14°C in albumen. The sleeves allowed one consistent approach to determining thermal death time kinetics regardless of viscosity.