Which of the following statements regarding thermal death kinetics of microorganisms is/are TRUE?
Options:
(A) The $D$-value is the heating time required at a given temperature to destroy $90\%$ of the microbial population (one log reduction)
(B) The $z$-value is the temperature increase required to reduce the $D$-value by a factor of 10
(C) Thermal death of vegetative cells and bacterial spores follows first-order reaction kinetics: $\ln(N/N_0) = -k t$
(D) Higher $z$-value indicates greater temperature sensitivity of the microorganism
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. $D$-value = time for 1 log ($90\%$) reduction: $D = t / \log_{10}(N_0/N)$ (A is true).
2. $z$-value = $\Delta T$ for 1 log change in $D$: $z = (T_2 - T_1) / \log_{10}(D_1/D_2)$ (B is true).
3. Semi-log linear survival curves confirm first-order inactivation kinetics (C is true).
4. A LOWER $z$-value means a smaller temperature rise causes a ten-fold drop in $D$, indicating HIGHER temperature sensitivity (D is false).