Fungal morphology and metabolite production in submerged mycelial processes.

Advances in citric acid fermentation by Aspergillus niger: biochemical aspects, membrane transport and modeling.

This Mini-Review summarizes the current knowledge on the biochemical and physiological events leading to massive citric acid accumulation by Aspergillus niger under industrially comparable conditions, thereby particularly emphasizing the roles of glycolytic flux and its control, excretion of citric acid from the mitochondria and the cytosol, and the critical fermentation variables The potential of novel techniques for metabolic analysis and genomic approaches in understanding this fermentation is also discussed

Aspergillus niger citric acid accumulation: do we understand this well working black box?

Fungal production of citric acid.

Citric acid is a commodity chemical produced and consumed throughout The World. It is used mainly in the food and beverage industry, primarily as an acidulant. Although it is one of the oldest industrial fermentations, its World production is still in rapid increasing. Global production of citric acid in 2007 was over 1.6 million tones. Biochemistry of citric acid fermentation, various microbial strains, as well as various substrates, technological processes and product recovery are presented. World production and economics aspects of this strategically product of bulk biotechnology are discussed.

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Citric acid production.

Immobilized cells of Aspergillus niger needed a lower initial sucrose concentration than free cells in order to obtain maximal yields of citric acid production. High sucrose concentrations led to reduced yields and increased polyol formation (glycerol, erythritol, arabitol). Continuous fermentation with media containing low sugar concentrations prevented the formation of polyols. The change from nitrogen-limited to phosphate-limited precultivation of immobilized spores significantly increased the productivity of the mycelium. The ratio of citric acid to residual sugar in the effluent distinctly lay in the direction of citric acid. Inside the alginate beads mainly large bulbous cells were observed.

Influence of sucrose concentration and phosphate limitation on citric acid production by immobilized cells of Aspergillus niger

The effect of different sucrose concentrations on the formation of polyols by Ca alginate entrapped Aspergillus niger was investigated. High sucrose concentrations led to an increase in polyol formation and a decrease in citric acid production. An increase in the ratio of glycerol to other polyols was also observed. Maximal productivity of A. niger was shifted to lower initial sucrose concentrations on immobilization.

S. Honecker

Papers

Influence of sucrose concentration and phosphate limitation on citric acid production by immobilized cells of Aspergillus niger

Formation of citric acid and polyols by immobilized cells of Aspergillus niger