Question Bank • QB_SUB_DFE_KNT_001 NAT • 2 Marks

Section 7: Dairy and Food Engineering

Microbial Inactivation Kinetics: D-Value, z-Value & F-Value

Subtopic: D-value change with temperature from z-value

Question Statement:

The decimal reduction time ($D$-value) for an index spore is $12.0\text{ min}$ at $110^\circ\text{C}$. If the thermal resistance constant is $z = 10^\circ\text{C}$, the $D$-value at $120^\circ\text{C}$ (in minutes) is:

Answer Key:

1.2

Step-by-Step Solution & Explanation

Thermal destruction relation: $\log_{10}\left(\frac{D_1}{D_2}\right) = \frac{T_2 - T_1}{z}$ $\log_{10}\left(\frac{12.0}{D_2}\right) = \frac{120 - 110}{10} = 1.0 \implies \frac{12.0}{D_2} = 10 \implies D_2 = 1.20\text{ min}$
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