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  Production of citric acid

Production of citric acid:

Citric acid that is a key intermediate of the TCA cycle is generated by fungi, yeast and bacteria. The raw material, mollases is diluted to 20-25 % sugar concentration and mixed with nitrogen source and other salts. The pH of the medium is lowered to pH 3.0.The fermentation is taken out either on the surface, submerged, or solid state circumstances. In the surface culture technique, shallow aluminum or stainless steel pans are filled with the growth medium, inoculated with fungal spores and permitted to ferment. In the submerged culture technique, the mold is cultured in fermenters beneath vigorous stirring and mixing, whereas in solid state fermentation, the mold is grown over carrier material like bagasse, and so on that is impregnated with fermentation medium.

The production of citric acid by A. niger is mainly influenced by the concentration of trace metals like manganese, iron, copper and zinc in the medium. A suitable concentration of such elements is necessary for good acid production. Though, excess materials are treated with either charcoal, ferrocyanide, chelating agents or cation exchange resins. In adding up of methanol of 3-4% concentration has been found to enhance the outcome of citric acid. The fermentation is an aerobic fermentation and, thus, adequate aeration is necessary for successful citric acid production.

In current years, the production of citric acid by yeast is profiting significance since many types of yeast like Candida, Hansenula have been found to generate citric acid from carbohydrates and hydrocarbons. Good outcome of citric acid from different raw materials by candida lipolytica has been reported. The mechanism by which such yeasts generate citric acid appears to be slightly distinct from the mechanism by which the fungi generate citric acid.

Later than the fermentation is over, calcium citrate is precipitated from the fermented broth through addition of calcium hydroxide. It is then filtered washed and treated with sulphuric acid to precipitate calcium sulphate. The solution having citric acid is then purified by treatment with ion exchange resins, charcoal and so on and finally crystallized.

Uses of citric acid:

1. Citric acid is employed in food, textile, beverage, pharmaceutical and detergent industries.
2. It is also increasingly employed in the elimination of toxic and corrosive gases in air.

 

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