Optimisation of fermentation conditions for gluconic acid production by a mutant of Aspergillus niger

Aspergillus niger ORS-4, isolated from the sugarcane industry waste materials was found to produce notable level of gluconic acid. From this strain, a mutant Aspergillus niger ORS-4.410 having remarkable increase in gluconic acid production was isolated and compared for fermentation properties. Among the various substrates used, glucose resulted into maximum production of gluconic acid (78.04 g/L). 12% concentration led to maximum production. Effect of spore age and inoculum level on fermentation indicated an inoculum level of 2% of the 4-7 days old spores were best suited for gluconic acid production. Maximum gluconate production could be achieved after 10-12 days of the fermentation at 30°C and at a pH of 5.5. Kinetic analysis of production indicated that growth of the mutant was favoured during initial stages of the fermentation (4-8 days) and production increased during the subsequent 8-12 days of the fermentation. CaCO₃ and varying concentrations of different nutrients affected the production of gluconic acid. Analysis of variance for the factors evaluated the significant difference in the production levels.