Possibilities of Redox Potential Regulation in Submerged Citric Acid Bioprocessing on Beet Molasses Substrate

Marin Berovič^1,2*, Marjana Rošelj² and Mojmir Wondra<sup>3

1</sup>Department of Chemical, Biochemical and Ecology Engineering, University of Ljubljana, Hajdrihova 19, SI-1115 Ljubljana, Slovenia
²National Institute of Chemistry, Ljubljana, Hajdrihova 19, SI-1115 Ljubljana, Slovenia
³Department of Food Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia

Article history:
Received September 16, 1999
Accepted May 17, 2000

Key words:
redox potential regulation, citric acid, beet molasses substrate

Summary:
In submerged citric acid production by Aspergillus niger on beet molasses substrate it has been found that for high yielding particular levels of the redox potential are of essential importance. Two maxima (260 and 280 mV) and two minima (180 and 80 mV) have to be obtained. Regulation of redox potential by chemical and physical methods was studied. Bioprocessing could be significantly improved by appropriate redox potential regulation. Chemical methods comprising addition of oxidants and reductants did not block microbial growth, but evidently inhibited citric acid biosynthesis. The physical method of regulation, by variation of agitation and aeration, was found the most effective and appropriate for high yield in citric acid biosynthesis.

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