Question Bank • QB_DFE_GATE_003 NAT • 2 Marks

Section 7: Dairy and Food Engineering

Preservation of Food

Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods

Question Statement:

A bacterial spore suspension has a $D_{121.1}$-value of $1.2\text{ minutes}$ and a $z$-value of $10^\circ\text{C}$. The $D$-value of the same bacterial spores at $111.1^\circ\text{C}$ is ________ minutes (in integer).

Answer Key:

12

Step-by-Step Solution & Explanation

Thermal Death $z$-value Equation: $\log_{10}(D_1 / D_2) = \frac{T_2 - T_1}{z} = \frac{121.1 - 111.1}{10} = 1 \implies \frac{D_1}{1.2} = 10 \implies D_1 = 12.0\text{ min}$ Hence, the $D$-value is **12** minutes.
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