# DBT JRF 2022 — Question 115

Exam: DBT JRF 2022 · Section: B · Topic: Industrial Microbiology › Citric Acid Fermentation · Difficulty: Medium

## Question

Commercial production of citric acid is done by fermentation using:

## Options

- **A.** Aspergillus niger
- **B.** Clostridium butyricum
- **C.** Saccharomyces cerevisiae
- **D.** Lactobacillus acidophilus

## Answer

Option A

## Explanation

Aspergillus niger for citric acid production: Citric acid (E330) is one of the most widely used food acidulants and is produced industrially by submerged fermentation: • Producing organism: Aspergillus niger (a filamentous fungus) • Carbon source: Sucrose (from sugarcane molasses) or glucose (from starch hydrolysate) • Conditions for maximum citric acid yield: - Low pH (<2.5): suppresses competing organic acids, inhibits phosphofructokinase, favouring citric acid accumulation - Low phosphate and manganese levels: reduces growth, redirects carbon to citric acid - High dissolved oxygen - High sugar concentration (15–20%) • Yield: >90% theoretical conversion of glucose to citric acid • Metabolic basis: Blocks in TCA cycle (low aconitase activity due to low Mn²⁺) cause citrate to accumulate. Global production: ~2 million tonnes/year; used in food, beverages, pharmaceuticals, cleaning products. Answer: Aspergillus niger produces citric acid by submerged fermentation with high yield under acidic, low-phosphate conditions.

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