acid, an unwanted byproduct. Selection for mutants with
very low aconitase activity has been used in attempts to
reduce production of isocitric acid.
Although many microorganisms can be used to produce
citric acid, A. niger remains the main industrial producer.
Specific strains that are capable of overproducing citric
acid have been developed for various types of fermentation
processes. The yield of citric acid from these strains often
exceeds 70% of the theoretical yield on the carbon source.
Despite a long and successful history of production of citric
acid, there is still no single explanation for the biochemical
basis of the process to consistently explain the observed
behavior of this fermentation. This review discusses the
biochemical factors that contribute to citric acid accumulation
in A. niger fermentations.