Citric Acid:

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.

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.

Wikipedia

Citric Acid Production by Aerobic Bioprocesses

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.

Bioreactor: batch or fed-batch (100m3)

A. niger spores/L (5.25X106) may be introduced to the fermentor.

Aeration is provided to the fermenter by air sparging (0.1-0.4 vvm)

Temperature is controlled by cooling coil.

Agitation: 50-100rpm 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

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.