Citric acid production by Aspergillus niger using media containing low concentrations of glucose or corn starch.

By using an appropriate ratio of carbon source to mineral components, we obtained comparable citrate yields in media containing different concentrations of glucose. The enzyme system of inoculum passed on gradually from "growth" state to "production" state during the mould growth. In the starch medium, the critical factors of citric acid production are the aeration efficiency of the medium and the amylase formation of the strain. The air interruption exhibited a prolonged inhibition of the production rate but not of the citrate yield in glucose medium while those parameters in starch medium containing excessive urea were briefly but severely inhibited. After being affected by these unfavorable conditions, the production activity of Aspergillus niger could be restored by applying an appropriate fermentation process.