D Value Formula Microbiology

Temperature or set of conditions to achieve a log reduction that is to kill 90 or 1 log of relevant microorganisms.

D value formula microbiology. Calculator for determining the decimal reduction time d for a microorganism at a higher temperature knowing the d value at a lower temperature and the z value. D reference temperature time log a log b. Total log reduction required for sterilization of the material with sal value of 10 6 2 73 6 8 73. D value is the time required to kill 90 of the spores or vegetative cells of a given microorganism at a specific temperature in a specific medium.

In microbiology d value refers to decimal reduction time or decimal reduction dose and is the time or dose required at a given condition e g. D value decimal reduction value it is the time required at temperature t to reduce a specific microbial population by 90 or by a factor of 10. The d value was determined by inoculating 100 ml of disinfecting solution with 1 ml of a bacterial suspension 104 105 cfu ml for vegetative and spore forms. It shows that only 2 73 log reduction is required to decrease the microbial population from 540 to 1.

Z value z value is the number of degrees of temperature change necessary to change the d value by a factor of 10. An introduction to d value the decimal reduction time as used in thermal processing of foods. Prior to the selection of disinfectants for low intermediate and high sterilizing levels the decimal reduction time d value for the most common and persistent bacteria identified at a health care facility should be determined. A d value is denoted with the capital letter d.

For example if a material has a bioburden of 540 cfu then to reduce the microbial population from 540 to 1 log 540 2 73. D values can be determined from survivor curves when the log of population is plotted against time or by the formula. D value or decimal reduction time is the time it takes to reduce a microbial population by 1 logarithm or 90 of its initial value under specified conditions e g sterilant concentration exposure temperature relative humidity package configuration.