Feedstocks for citric acid fermentation by Aspergillus niger: which option correctly lists commonly used carbohydrate substrates?

Introduction / Context:
Citric acid is a high-volume organic acid produced using carbohydrate-rich feedstocks. Process economics and availability determine whether molasses, refined sugars, or enzymatically hydrolyzed starch syrups are used. Aspergillus niger adapts well to each of these substrates under controlled conditions.

Given Data / Assumptions:

• Organism: A. niger optimized for citric acid overflow metabolism.
• Potential feedstocks: beet molasses, sucrose, starch hydrolysate (glucose syrup).
• Process control: low metal ions, appropriate pH, and aeration.

Concept / Approach:
All three listed carbohydrate sources are standard industrial feedstocks. Molasses provides a low-cost, mineral-rich substrate (metals must be controlled), sucrose offers consistency, and starch hydrolysate is widely used where corn or cassava starch is abundant.

Step-by-Step Solution:

Verification / Alternative check:
Industrial case studies across regions employ all three feedstocks successfully for citric acid production.

Why Other Options Are Wrong:

• Single-source options ignore the flexibility of the process.
• Whey/lactose is atypical for citric acid with A. niger.

Common Pitfalls:
Neglecting impurity control with molasses; failing to ensure adequate aeration and metal limitation for high yields.

Final Answer:
All of these (beet molasses, sucrose, and starch hydrolysate)