Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods
Question Statement:
The thermal resistance parameter $z$-value is defined as the temperature change required to:
Options:
(A) Change the decimal reduction time ($D$-value) by a factor of 10 (one log cycle)
(B) Kill $90\%$ of the microbial population at a fixed temperature
(C) Double the enzyme reaction rate
(D) Reduce moisture content by $10\%$
Answer Key:
A
Step-by-Step Solution & Explanation
By definition, the $z$-value is the temperature increase (in $^\circ\text{C}$ or $\text{K}$) necessary to achieve a 10-fold (one decimal log cycle) reduction in the $D$-value on a thermal death time curve.