Monday, 5 December 2011


The first ever commercial production of citric acid was launched in UK by Sturage Company by JOHN & EDMUND; 1826
In 1880; Citric acid was first synthesised from glycerol
In 1893; Wehmer observed occurrence of citric acid as a microbial product by using penicillium.
In 1922; Millard recorded accumulation of citric Acid In culture of Aspergillus niger under condition of nutrition deficiency.
In 1923; Pfizer began fermentation based process in USA
1.      Fermentation:  A. niger is the choice for production of citric acid for several decades. Large number of other microbes such as P.luteum, P.cirinum, pichia spp. Have also been used. Fermentation can be carried out by any of following processes:
a)      KOJI PROCESS (solid state fermentation): it’s a Japanese process in which special strains of A.niger are used with solid substrate such as sweet potato starch. Mold is used to which wheat bran was substituted. The pH of bran was adjusted between 4–5 and additional moisture is picked up during steaming so as to get water content of mash around 70 – 80%. After cooling the bran to 30 – 60oC the mass is inoculated with KOJI which was made by a special strain of A.niger. Since bran contains starch which on saccharification produces citric acid by amylase of A.niger.  Bran after inoculation is spread in trays to a depth of 3 – 5 cm and kept for incubation at 25-30oC. After 5 – 8 days koji is harvested and citric acid is extracted.
b)      Liquid Surface Culture Process: in this case aluminium or stainless steel shallow pans or trays are used. Sterilized medium contains molasses and salts. Fermentation is usually carried out by blowing spores of A.niger over the surface of the solution for 5-6days. Spore germination occurs within 24 hours and a white mycelium grows over the surface of the solution. After 8-10days of inoculation liquid can be drained off and citric acid can be extracted from the mycelia mat.
c)      Submerged Culture Process: this method is quite economical. In this case A. japonicus (black mold) is slowly bubbled in a stream of air through a culture solution. Since organism shows subsurface growth and produces Citric acid in culture solution the yields are inferior in comparison to liquid surface culture fermentation.

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