A high performance fermentation process for citric acid production by Aspergillus niger NGGCB-101, using vermiculite as an additive in a stirred bioreactor

The present study describes the use of vermiculite for enhanced citric acid productivity by a mutant strain of Aspergillus niger NG(GCB)-101 in a stirred bioreactor of 15.01 capacity. The maximum amount of citric acid (96.10 g/l) was obtained with the control 144 h after mycelial inoculation. To enhance citric acid production, varying levels of vermiculite were added as an additive into the fermentation medium. The best results were observed when 0.20 mug/l vermiculite was added into the medium 24 h after inoculation resulting in the production of 146.88 g citric acid monohydrate/l. The dry cell mass and residual sugar were 11.75 and 55.90 g/l, respectively. Mixed mycelial pellets (1.08-1.28 mm, dia) were observed in the fermented culture broth. When the culture grown at different vermiculite levels was monitored for Q(p), Q(s) and q(p), there was a significant enhancement (P less than or equal to 0.05) in these variables over the control (vermiculite-free). Based on these results, it is concluded that vermiculite might affect mycelial morphology and subsequent TCA cycle performance to improve carbon source utilization by the mould, basic parameters for high performance citric acid fermentation.