Z value is the
temperature required to increase the thermal destruction by one log. In simple
words we can say the temperature required to increase the death rate or D value
of the organisms by 10 times.
Z value is
required to determine the F0 value for the sterilization process. Biological indicators are tested to determine their Zvalue. Every microorganism has is
unique Zvalue.
Dvalue of the organism is determined at different (three or more) temperatures (i.e 121°C, 124°C, 129°C). A graph is plated between
these D values and temperature. This curve is known as thermal death curve. It is
easy to determine the Zvalue graphically then mathematically. Temperature is determined by graph that is required for 1 log reduction as shown in figure.
FDA guides the Biological Indicator manufacturers
You should provide Zvalues for thermal processes. FDA generally recommends that Biological Indicators have a minimum Zvalue of 10°C. To determine the Zvalue, you should construct a thermal resistance curve. The thermal resistance curve is a semilogarithmic graph of Dvalue vs. temperature. The Zvalue can be obtained from the slope of the curve by calculating the number of degrees of temperature for a 1logarithm change in Dvalue. The greater the number of temperatures studied, the more accurate the resulting Zvalue. FDA recommends that studies use at least three different temperatures.Also see: Testing of Biological Indicators
Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widelyread pharmaceutical blog since 2008. Signup for the free email updates for your daily dose of pharmaceutical tips.
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