Subtopic: Kinetics of microbial death – pasteurization and sterilization of milk and other liquid foods
Question Statement:
Bacillus stearothermophilus has a z value of 10.20 °C at a reference temperature of 121 °C. The z value of the same organism at a reference temperature of 135 °C is
Options:
(A) 9.73 °C
(B) 10.20 °C
(C) 10.95 °C
(D) 11.15 °C
Official Answer Key:
C
Step-by-Step Solution & Explanation
Using the E_a computed in Q82 (≈291.4 MJ/kg-mole) and applying the same relation at the new reference temperature T₂=135+273=408 K: z₂ = 2.303·R·T₂²/E_a = 2.303×8.314×408²/291,404 = 2.303×8.314×166,464/291,404 = ≈10.95 °C, matching option (C) — the z-value increases slightly at the higher reference temperature, consistent with the quadratic T-dependence in the z–E_a relation.
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