Question

If the log of microorganisms is plotted against time, an initially straight line results. The inverse slope of this line is called

• A. Thermal death line
• B. D value
• C. Z value
• D. Half-life

Hint:

D value helps in assessing the heat resistance of microorganisms and in establishing sterilization parameters.

Answer 1

The Correct Option is B

In microbiology and sterilization kinetics, when the logarithm of the number of surviving microorganisms is plotted against time during a thermal death process, the plot often yields a straight line initially. This linear portion represents a first-order kinetics death rate. The slope of this line represents the rate of microbial death, and the inverse of the slope is termed the D value (decimal reduction time). The D value is defined as the time required at a specific temperature to reduce the microbial population by 90%, or one logarithmic cycle (i.e., reduce the number of viable organisms to 10% of the original count). Other terms: - Thermal death line represents the graphical representation of thermal death times at various temperatures. - Z value is the temperature change needed to change the D value by a factor of 10. - Half-life is the time needed for half the microbial population to be killed, different from the decimal reduction time. Thus, the D value is crucial in designing sterilization processes to ensure effective microbial kill in pharmaceutical and food industries.