"F₀" is defined as the number of equivalent minutes of steam sterilization at temperature 121.1 °C (250 °F) delivered to a container or unit of product calculated using a z-value of 10 °C. The term F-value or "F_Tref/z" is defined as the equivalent number of minutes to a certain reference temperature (T_ref) for a certain control microorganism with an established Z-value. Z-value is a term used in microbial

thermal death time Thermal death time is how long it takes to kill a specific bacterium at a specific temperature. It was originally developed for food canning and has found applications in cosmetics, producing salmonella-free feeds for animals (e.g. poultry) and phar ...

calculations. It is the number of degrees the temperature has to be increased to achieve a tenfold (i.e. 1 log₁₀) reduction in the D-value. The D-value of an organism is the time required in a given medium, at a given temperature, for a ten-fold reduction in the number of organisms. It is useful when examining the effectiveness of thermal inactivations under different conditions, for example in food cooking and preservation. The z-value is a measure of the change of the D-value with varying temperature, and is a simplified version of an

Arrhenius equation In physical chemistry, the Arrhenius equation is a formula for the temperature dependence of reaction rates. The equation was proposed by Svante Arrhenius in 1889, based on the work of Dutch chemist Jacobus Henricus van 't Hoff who had noted in 18 ...

and it is equivalent to z=2.303 RT T_ref/E.Holdsworth S.D, Aseptic Processing and Packaging of Food Products, 1992. , 9781851667758 The z-value of an

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

in a particular medium is the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

change required for the D-value to change by a factor of ten, or put another way, the temperature required for the

thermal destruction curve A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

to move one log cycle. It is the reciprocal of the slope resulting from the plot of the logarithm of the D-value versus the temperature at which the D-value was obtained. While the D-value gives the time needed at a certain temperature to kill 90% of the organisms, the z-value relates the resistance of an organism to differing temperatures. The z-value allows calculation of the equivalency of two thermal processes, if the D-value and the z-value are known. Example: if it takes an increase of 10 °C (18 °F) to move the curve one log, then our z-value is 10. Given a D-value of 4.5 minutes at 150 °C, the D-value can be calculated for 160 °C by reducing the time by 1 log. The new D-value for 160 °C given the z-value is 0.45 minutes. This means that each 10°C (18 °F) increase in temperature will reduce our D-value by 1 log. Conversely, a 10 °C (18 °F) decrease in temperature will increase our D-value by 1 log. So, the D-value for a temperature of 140 °C would be 45 minutes.

References

General references

* * {{DEFAULTSORT:Z-Value Biology terminology de:Dezimale Reduktionszeit#Z-Wert

See also

References

General references