Stimulatory effect of alcohols (methanol and ethanol) on citric acid productivity by a 2-deoxy -glucose resistant culture of Aspergillus niger GCB-47

The present study describes citric acid fermentation by Aspergillus niger GCB-47 in a 15-l stainless steel stirred fermentor. Among the alcohols tested as stimulating agents, 1.0% (v/v) methanol was found to give maximum amount of anhydrous citric acid (90.02±2.2 g/l), 24 h after inoculation. This yield of citric acid was 1.96 fold higher than the control. Methanol has a direct effect on mycelial morphology and it promotes pellet formation. It also increases the cell membrane permeability to provoke more citric acid excretion from the mycelial cells. The sugar consumed and % citric acid was 108±3.8 g/l and 80.39±4.5%, respectively. The desirable mycelial morphology was in the form of small round pellets having dry cell mass 14.5±0.8 g/l. Addition of ethanol, however, did not found to enhance citric acid production, significantly. The maximum value of Yp/x (i.e., 5.825±0.25 g/g) was observed when methanol was used as a stimulating agent. The best results of anhydrous citric acid were observed, 6 days after inoculation when the initial pH of fermentation medium was kept at 6.0.