The Effect of Copper (II) ion on the Production of Citric Acid by Aspergillus niger using Corncobs

Abstract

Citric acid production using agro-waste as cheap carbon source helps in waste management and reduction in cost of production. The study was aimed at optimizing citric acid production from corncobs as substrate was amended with copper ions. Corncobs were collected, air dried, milled and pretreated with acid hydrolysis. The pretreated corncob media were inoculated with 106 spores/ml of Aspergillus niger and fermented for 10 d at 28 \(\pm\) 2 °C. Effect of corncob concentrations of 5 – 25 % w/v on citric acid production was examined. The concentration with highest yield of citric acid was optimized using copper ions concentration of 0 – 0.4 g/l. All through the fermentation processes samples analyzed were citric acid produced, fungal biomass, and changes in pH. The supplemented corncob medium had the highest citric acid production and fungal biomass after 8 d of fermentation. Studies on corncob concentrations showed that 25 %w/v of corncobs had the highest citric acid production and fungal biomass. The highest citric acid production and fungal biomass of 2.94\(\pm\) 0.05 and 3.11\(\pm\) 0.04 g/l respectively were observed in the medium amended with 0.3 g/l of copper ions. Statistically, the values were significantly different from other concentrations of copper ions (p< 0.05). Corncob was observed to be a good substrate for citric acid production by A. niger and amendment of substrate with copper ions at lower concentration can help to optimize the production of citric acid.