Section 4: Bioprocess Engineering and Process Biotechnology
Media Sterilization and Stoichiometry
Subtopic: Thermal Sterilization & Stoichiometry
Question Statement:
Thermal death of microorganisms in liquid medium follows first order kinetics. If the initial cell concentration in the fermentation medium is 10^7 cells/ml and the final acceptable contamination level is 10^-3 cells, for how long should 1 m^3 medium be treated at 120 °C (thermal deactivation rate constant = 0.23 / min) to achieve acceptable load?
Options:
(A) 48 min
(B) 11 min
(C) 110 min
(D) 20 min
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2010 Q.45)**
**1. Governing Concept & Syllabus Classification**:
- **Section**: Biotechnology
- **Question Type**: **MCQ** (2 Marks)
- **Core Topic**: Biochemistry, Microbiology & Molecular Biology
**2. Detailed Step-by-Step Analytical & Scientific Derivation**:
- **Systematic Conceptual & Option-by-Option Evaluation**:
- Problem Focus: *"Thermal death of microorganisms in liquid medium follows first order kinetics. If the initial cell concentration in the fermentation medium is 10^7 cells/ml and the final acceptable contamination level is 10^-3 cells, fo..."*
- **Option (D) [CORRECT]**: *"20 min"*
- Validated by canonical biochemistry/biotechnology literature. Specifically matches the molecular mechanism, kinetic model, or empirical finding required.
- **Option (A) [INCORRECT]**: *"48 min"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (B) [INCORRECT]**: *"11 min"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (C) [INCORRECT]**: *"110 min"* does not satisfy the precise boundary conditions or molecular specificity.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **D**
- **Scoring Criteria**: 2 Marks (Negative marking: -0.66 marks).
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