Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods
Question Statement:
Which of the following statements regarding thermal processing parameters ($D$, $z$, and $F$ values) is/are correct?
Options:
(A) The $D$-value is the heating time required at a given temperature to destroy $90\%$ of a microbial population.
(B) The $z$-value represents the temperature increase required to reduce the $D$-value by a factor of 10.
(C) A higher $z$-value indicates higher temperature sensitivity of the microorganism.
(D) The standard reference temperature for calculating $F_0$ value in thermal sterilization of low-acid foods is $121.1^\circ\text{C}$ ($250^\circ\text{F}$).
Answer Key:
A, B, D
Step-by-Step Solution & Explanation
• $D$-value is time for 1-log (90%) reduction (A is correct).
• $z$-value is temperature change required for a 1-decade change in $D$-value (B is correct).
• A lower $z$-value implies that a smaller temperature rise causes a tenfold drop in $D$-value, meaning GREATER temperature sensitivity (so C is incorrect).
• $F_0$ is defined at reference temperature $121.1^\circ\text{C}$ ($250^\circ\text{F}$) with $z = 10^\circ\text{C}$ (D is correct).