In aerobic yeast fermentation for citric acid production from alkanes using a fed-batch strategy, why must alkanes be fed slowly rather than added rapidly?

Introduction:
Fed-batch feeding of hydrophobic substrates like alkanes is a classic strategy in aerobic fermentations producing organic acids. Rapid addition can disrupt mass transfer and cell physiology, leading to lower productivity and unstable operations.

Given Data / Assumptions:

• Substrate: alkanes (hydrophobic, oxygen-demanding oxidation).
• Organism: aerobic yeast engineered or selected for citric acid production.
• Process: fed-batch with controlled substrate feed.

Concept / Approach:
High instantaneous alkane concentrations form surface films and large droplets, inhibiting cells and suppressing k_La by blocking gas–liquid interfaces. This reduces oxygen transfer rates precisely when oxygen demand is high, causing metabolic stress and reduced citric acid formation. Slow, controlled feeding maintains manageable interfacial areas and avoids toxic local concentrations.

Step-by-Step Solution:

Verification / Alternative check:
Dissolved oxygen profiles show sharp drops after rapid hydrocarbon pulses; controlled feeds maintain DO and steady citric acid productivity, validating the rationale.

Why Other Options Are Wrong:

• Citric acid toxicity: At controlled levels, product toxicity is not the main reason for slow alkane feeding.
• Foaming: Possible, but not the fundamental control reason.
• Excessive growth rate: Not the core issue; oxygen transfer inhibition is primary.

Common Pitfalls:
Ignoring emulsification strategy and surfactant selection; poor dispersion exacerbates O2 transfer problems even with slow feeding.

Final Answer:
Fast addition of alkanes will inhibit the cells and reduce oxygen transfer rates