Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods
Question Statement:
The decimal reduction time ($D$-value) of a bacterial culture is $10.0\text{ min}$ at $110^\circ\text{C}$ and drops to $1.0\text{ min}$ at $120^\circ\text{C}$. The thermal resistance constant ($z$-value) in $^\circ\text{C}$ is ________ (answer in integer).
Answer Key:
10
Step-by-Step Solution & Explanation
By definition, the $z$-value is the temperature change required for a 10-fold (one log cycle) change in decimal reduction time $D$:
$z = \frac{T_2 - T_1}{\log_{10}(D_1 / D_2)} = \frac{120^\circ\text{C} - 110^\circ\text{C}}{\log_{10}(10.0 / 1.0)} = \frac{10^\circ\text{C}}{1} = 10^\circ\text{C}$