Screening and Improvement of Local Isolates of Aspergillus Niger for Citric Acid Production

The study involved the screening of fourteen isolates of Aspergillus niger for citric acid production from glucose. The study was aimed at screening and improving local strains of Aspergillus niger with potential for citric acid production. All the isolates screened produced varying amounts of citric acid, the highest was by the isolate designated CP3 which produced 12.81g/l and the least was B11 and O12 which produced 3.42g/l all after 6 days of submerged fermentation. The isolate CP3 was chosen for further studies. Strain improvement studies which was based on exposure of CP3 to ultraviolet irradiation for 10, 30 and 45 minutes increased citric acid yield to 22.20g/l (48.89% increase) by mutant M45 followed by a citric acid yield of 16.22g/l by the 30 minutes mutant (M30) and the least being M10 which produced 13.66g/l in all cases after 6 days of fermentation. The mutant (M45) also yielded higher amount of citric acid (19.64g/l) without methanol as additive compared to the parent strain (CP3) which gave a citric acid of 14.94g/l with the addition of methanol after six days (144h) of fermentation in both cases. Finding from this study showed that all the isolates have potential for citric acid production.Keywords: Isolation, Screening, Improvement, Aspergillus niger, Citric acid