Dear colleagues,
I am trying to standardize bacterial reduction after UV treatments. UV doses and log reductions for each dose are known, but log reductions in food are often non-linear because food matrices are complex and the inactivation of microorganisms is attenuated in higher doses. One example of this can be the next paper, in which some bacteria are disinfected in a J pattern and others in a reverse-S shape: Article Investigating the Use of Ultraviolet Light Emitting Diodes (...
How can I calculate the decimal reduction dose in these cases?
The decimal reduction dose (D-value) is a measure of the effectiveness of a non-linear logarithmic reduction treatment, which is typically used in microbiology to determine the amount of radiation, heat, or chemical treatment needed to reduce the number of microorganisms by 90%. The D-value is calculated using the following formula:
D = (log N0 - log N1) / k
Where:
- D is the decimal reduction dose (in the unit of the treatment)
- N0 is the initial number of microorganisms
- N1 is the number of surviving microorganisms after treatment
- k is the slope of the logarithmic reduction curve (also known as the "death rate constant")
To calculate the D-value, you will need to perform a series of experiments where you expose a known number of microorganisms to different doses of the non-linear logarithmic reduction treatment, and then count the number of surviving microorganisms at each dose. You can then plot the data on a logarithmic scale, and determine the slope of the curve using linear regression analysis.
Once you have the slope (k) of the logarithmic reduction curve, you can use the above formula to calculate the D-value for a given treatment. For example, if you have determined that the D-value for a particular radiation treatment is 10 kGy, then you would need to apply a dose of 10 kGy to achieve a 90% reduction in the number of microorganisms.
Note that the calculation of the D-value assumes that the reduction in microorganisms is a stochastic process that follows a logarithmic distribution. The actual reduction may be affected by other factors, such as the age and physiological state of the microorganisms, the presence of protective materials, and the environmental conditions during treatment.
Lassaad Hedhili Thank you for your answer. However, when log reduction has 2 or 3 stages with different k, do I have to mention the D-value as the first linear stage or using all the data obtained? If it is the latest, as more experiments are done, the more attenuated the D-value is, but if I only take into account the first stage, only one part of the reality will be shown.
El concepto de D sólo se puede aplicar cuando hay una relación lineal entre log(N/No) y el tiempo (p.e.).Generalmente, cuando se aplica una tecnología no térmica, la relación no es lineal y por tanto no se puede aplicar el concepto D. Para ello debes ajustar a un modelo no lineal (p.e. Weibull) y ver cómo se comportan los parámetros.
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