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Biosynthesis of Citric Acid

Citric acid is widely used in various branches of economy, particularly in food production (confectionery, soft drinks, wine clarification), medicine, production of shampoos and cosmetics, tanning, photosensitive emulsions, etc. Until 1930’s, citric acid was derived from lemons and the production monopoly belonged to Italy. In mid-30’s, the Czech Republic undertook production of citric acid by microbiological method from raw stuff containing sugar.

In 1948, Latvian scientists pioneered the production of citric acid from molasses, spin-off of sugar production, in the former USSR. They obtained it by microbiological biosynthesis, using Aspergillus niger microorganism.

Riga Citric Acid Plant elaborated an economic technology for yielding crystalline citric acid and did serious work on obtaining highly productive Aspergillus niger strains – R3, R5, R6.

The essence of the invention:

  • The citric acid producer Aspergillus niger strain R-5 put into practice in microbiological production is the most productive one in our country and behind Latvia borders. The know-how is applied to microorganisms selection and use of strain R-5 for citric acid production from sugar-cane molasses. Producers' inoculum material productivity is 0.7-1.0 g spores of 1 dm2 sporulation medium surface. This know-how enables the possibility to increase the productivity of citric acid production from sugar-cane molasses;
  • The know-how gives the possibility to increase the yield of spores seeding material from sporulation surface and to obtain 1.85-1.95 spores from 1 dm2, by application of mold Aspergillus niger strain R-6, that under fermentation conditions gives citric acid yield 95-100% from sugar beet or sugar cane molasses. Strain R-6 can be applied to citric acid production under surface or submerge fermentation conditions.


  • Licences for the developed technology and selected Aspergillus niger producers were sold to foreign companies in Bulgaria, France, Slovenia, Slovakia, Turkey and India.
  • Several plants were set up in Russia, Belarus and Armenia on the grounds of citric acid technology developed in Riga.
  • Riga Citric Acid Plant is the only producer of citric acid in the Baltic States.

The main authors:

Patent documents:

  • 59 Author’s Certificates of USSR and 39 patents of other countries.