Aspergillus niger amylase from starch is commonly run in fed-batch. What is the core process reason: why modulating feed improves performance compared to batch?

Introduction / Context:
Filamentous fungi such as Aspergillus niger secrete amylases when grown on starch. However, high bulk starch makes the broth viscous and can repress enzyme synthesis via catabolite repression. Fed-batch feeding keeps the inducer/substrate in an optimal range.

Given Data / Assumptions:

• Starch is both substrate and inducer for amylase expression.
• High starch raises viscosity and can cause mass-transfer and mixing problems.
• Excess soluble sugars from rapid hydrolysis can repress enzyme formation.

Concept / Approach:
In fed-batch, starch (or liquefied feed) is dosed gradually to maintain low bulk concentration: this lowers apparent viscosity, eases aeration/agitation, and avoids catabolite repression while sustaining induction. Batch with high starting starch risks poor oxygen transfer and repressed enzyme expression. Continuous CSTRs can dilute inducer below the induction threshold and complicate washout/productivity trade-offs.

Step-by-Step Solution:

Verification / Alternative check:
Industrial enzyme processes often show higher volumetric productivity with fed-batch feeding of polymeric substrates.

Why Other Options Are Wrong:

• Preventing “any fermentation” is not the goal and is incorrect.
• CSTR superiority here is not general; washout and dilution can hurt induction.
• “All of the above” includes false statements; high initial starch is not universally preferred.

Common Pitfalls:
Assuming more substrate is always better; for viscous broths and inducible enzymes, controlled feeding wins.

Final Answer:
Fed-batch minimizes starch concentration, reducing medium viscosity and catabolite repression.