1. Industrial Production of Citric Acid
Application of Citric Acid: (text,p.524)
Acidulant in food, confectionary, and beverage (75%)
Pharmaceutical (10%), e.g. soluble aspirin preparation
- industrial (15%): complexes with metals such as iron and copper to be stabilizer of oil and fats.

2. Citric Acid Production by Aerobic Bioprocesses
Wikipedia

3. Industrial Production of Citric Acid
Microorganism: Aspergillus niger (mainly), Candida yeast (from carbohydrates or n-alkanes)
Citric acid production is mixed growth associated, mainly take place under nitrogen and phosphate limitation after growth has ceased.
Medium requirements for high production
- Carbon source: molasses or sugar solution.
- Na-ferrocyanide is added to reduce Iron (1.3 ppm) and manganese (<0.1ppm).
- High dissolved oxygen concentration
- High sugar concentration
- pH<2
- 30 oC.

4. Industrial Production of Citric Acid
Bioreactor: batch or fed-batch (100m3)
5-25X106 A. niger spores/L may be introduced to the fermentor.
Aeration is provided to the fermenter by air sparging ( vvm)
Temperature is controlled by cooling coil.
Agitation: rpm to avoid shear damage on molds.
Fed-batch is used to reduce substrate inhibition and prolong the production phase one or two days after growth cessation.
Volumetric yield: 130 kg/m3
Limitation of nitrogen and phosphate provoke an overflow in metabolism that results in an overproduction of citric acid.

5. Industrial Production of Citric Acid
Separation:
- The biomass is separated by filtration
- The liquid is transferred to recovery process:
- Separation of citric acid from the liquid: precipitation
calcium hydroxide is added to obtain calcium citrate
tetrahydrate → wash the precipitate→ dissolve it with
dilute sulfuric acid, yield citric acid and calcium
sulfate precipitate → bleach and crystallization →
anhydrous or monohydrate citric acid.