Abstract
Citric acid is regarded as a metabolite of energy metabolism, of which the concentration will rise to appreciable amounts only
under conditions of substantive metabolic imbalances. Citric acid fermentation conditions were established during the 1930s and
1940s, when the effects of various medium components were evaluated. The biochemical mechanism by which Aspergillus niger
accumulates citric acid has continued to attract interest even though its commercial production by fermentation has been established
for decades. Although extensive basic biochemical research has been carried out with A. niger, the understanding of the events
relevant for citric acid accumulation is not completely understood. This review is focused on citric acid fermentation by A. niger.
Emphasis is given to aspects of fermentation biochemistry, membrane transport in A. niger and modeling of the production process.
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