GATE AG 2020 • Q35 NAT • 1 Mark

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 milk plant pasteurizes 12,500 L whole milk to inactivate Coxiella burnetii (D=14 s at 72°C), packed in 500 mL pouches, initial count 10/mL. Find the process F-value (s) required so that no package contains a survivor.

Official Answer Key:

126 to 126

Step-by-Step Solution & Explanation

To guarantee (with the standard microbiological safety margin) that essentially no package retains a viable organism, the process is designed for a 9-decimal (10⁻⁹, i.e., 1-in-a-billion) reduction in the target organism's population — regardless of the exact initial load, this convention gives F = 9×D = 9×14 = 126 s.

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