Production of Citric Acid from a New Substrate, Undersized Semolina, by Aspergillus niger

Emine Alben and Osman Erkmen*

Department of Food Engineering, Faculty of Engineering, University of Gaziantep, TR-27310 Gaziantep, Turkey

Article history:
Received: October 2, 2003
Accepted: February 16, 2004

Key words:
citric acid, undersized semolina, Aspergillus niger, fermentation

Summary:
The production of citric acid from fermentation medium (mass per volume ratio 0.01 % of undersized semolina) by Aspergillus niger was studied by shake culture method. The effects of initial pH (4.5, 5.5 and 6.5), methanol (volume fraction 1.0, 2.0 and 3.0 %) and ammonium nitrate (mass per volume ratio 0.01 %) on the production of citric acid were investigated. Citric acid concentration, biomass concentration and the amount of total carbohydrates (as glucose) were determined during fermentation period. About 0.04, 0.0448 and 0.0506 g/L of citric acid was produced in fermentation medium with initial pH=4.5, 5.5 and 6.5, respectively. Citric acid and biomass concentrations were increased with the addition of methanol and ammonium nitrate. The yield of citric acid based on consumed sugar was about 21.9 % in the presence of 3.0 % methanol and 0.01 % ammonium nitrate in fermentation medium with initial pH=6.5. 

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