The new D-value for 160 ☌ given the z-value is 0.45 minutes. Given a D-value of 4.5 minutes at 150 ☌, the D-value can be calculated for 160 ☌ by reducing the time by 1 log. The z-value allows calculation of the equivalency of two thermal processes, if the D-value and the z-value are known.Įxample: if it takes an increase of 10 ☌ (18 ☏) to move the curve one log, then our z-value is 10. 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. 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. The z-value of an organism in a particular medium is the temperature 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 to move one log cycle. 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 and it is equivalent to z=2.303 RT T ref/E. It is useful when examining the effectiveness of thermal inactivations under different conditions, for example in food cooking and preservation. 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 the number of degrees the temperature has to be increased to achieve a tenfold (i.e. Z-value is a term used in microbial thermal death time calculations. 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. "F 0" is defined as the number of equivalent minutes of steam sterilization at temperature 121.1 ☌ (250 ☏) delivered to a container or unit of product calculated using a z-value of 10 ☌. ( April 2018) ( Learn how and when to remove this template message) Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations.
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