Gamma-Ray Induced Mutants 14/20 and 79/20 of Aspergillus niger Increases Citric Acid Production from Molasses and Pumpkin

Among the various fungal strains screened for citric acid production, Aspergillus niger is known to produce considerable amounts of citric acid and other organic acids when cultivated in carbohydrate-rich medium of fermentation. A number of indigenous raw materials such as cane molasses and pumpkin have been carried out in present study for citric acid production by using gamma ray induced mutant strains 14/20 and 79/20 of Aspergillus niger under surface culture condition. Aiming to further increase the production of citric acid, the previously isolated gamma-ray induced second step mutant 14/20 and 79/20 of A. niger was reradiated at 10, 20, 30 and 40 Krad by Co Gamma beam-650 source at a dose rate of 0.674 kGy/hr. In absence of Prescott 60 salt highest production of citric acid was found by further mutated A. niger 14/20 with gamma radiation at 20 Krad in mixed fermentation medium which was about 19.32 mg/ml and lowest citric acid production was found in molasses media by further mutated A. niger 14/20 with gamma radiation at 10Krad which was found 9.65 mg/ml on the day 13 but it was higher fermentation of citric acid than by the unirradiated strain. In absence of Prescott salt higher production of citric acid was found by further mutated A. niger 79/20 with gamma radiation at 20 Krad in mixed fermentation medium than A. niger 79/20 which was about 17.58 mg/ml. Lowest citric acid production was found in molasses media by further mutated A. niger 79/20 with gamma radiation at 10 Krad which was found 8.92 mg/ml on the day 13 but it was higher fermentation of citric acid than by the unirradiated strains.