Allied & ICAR Exam Bank • ALLIED_1306 NAT • 2 Marks

Section 7: Dairy and Food Engineering

Thermal Processing and Kinetics

Subtopic: z-Value Calculation

Question Statement:

For a heat-resistant bacterial spore, the $D$-value at $110^\circ\text{C}$ is $D_{110} = 10.0\text{ minutes}$ and at $120^\circ\text{C}$ it is $D_{120} = 1.0\text{ minute}$. The thermal resistance constant ($z$-value in degrees Celsius) is:

Answer Key:

10.0

Step-by-Step Solution & Explanation

$z = \frac{T_2 - T_1}{\log_{10}(D_1 / D_2)} = \frac{120 - 110}{\log_{10}(10.0 / 1.0)} = \frac{10}{\log_{10}(10)} = \frac{10}{1} = 10.0^\circ\text{C}$.
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