Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods
Question Statement:
In the thermal processing of food products, which of the following definitions and relations are CORRECT?
Options:
(A) The decimal reduction time ($D$-value) is the time required at a given temperature to destroy $90\%$ of the microbial population
(B) The thermal resistance constant ($z$-value) is the temperature change required to alter the $D$-value by a factor of 10
(C) The $12D$ concept in low-acid canned food sterilization is designed to achieve a 12-decimal cycle reduction in Clostridium botulinum spores
(D) A higher $z$-value indicates that the target microorganism is more sensitive to temperature increases
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. By definition, $D = \frac{t}{\log_{10}(N_0 / N)}$. For a $90\%$ kill, $N/N_0 = 0.1$, so $\log_{10}(10) = 1$, giving $t = D$. (Statement A True)
2. The $z$-value is defined as $z = \frac{T_2 - T_1}{\log_{10}(D_1 / D_2)}$, representing the temperature increase needed for a 10-fold reduction in $D$. (Statement B True)
3. The commercial sterility standard for low-acid canned foods requires a minimum $12D$ process for *Clostridium botulinum* to prevent lethal botulism toxin production. (Statement C True)
4. A larger $z$-value means a greater temperature change is needed to change $D$ by 10-fold, indicating *lower* temperature sensitivity. A smaller $z$-value denotes greater sensitivity. (Statement D False)