Abstract: The potential of corn cobs as solid substrates for the production of citric acid was investigated using Aspergillus niger KA88, a local isolate as the fermenting organism. One-factor-at-a-time (OFAT) model was used to optimize the fermentation media to achieve the maximum yield of citric acid. The fermentation parameters studied and their resultant optimised levels were found to be 28 °C incubation temperature, 15% (w/v) sucrose for 6 days fermentation period, 50% each of (0.5-1mm and 3-5mm) particle sizes. Di-ammonium hydrogen phosphate was the preferred nitrogen source at a concentration of 4g/l. The final OFAT fermentation media gave 138.24 g anhydrous citric acid/kg dry corn cob. In general, corn cob proved to be a highly promising solid substrate for commercial citric acid production.

Keywords: Substrate, Aspergillus niger, fermentation, Temperature, One-factor-at-a-tme model.