Citric acid production from sugar cane molasses by 2-deoxyglucose-resistant mutant strain ofAspergillus niger

Citric acid production from sugar cane molasses byAspergillus niger NIAB 280 was studied in a batch cultivation process. A maximum of 90 g/L total sugar was utilized in citric acid production medium. From the parental strainA. niger, mutant strains showing resistance to 2-deoxyglucose in Vogal's medium containing molasses as a carbon source were induced by γ-irradiation. Among the new series of mutant strains, strain RP7 produced 120 g/L while the parental strain produced 80 g/L citric acid (1.5-fold improvement) from 150 g/L of molasses sugars. The period of citric acid production was shortened from 10 d for the wild-type strain to 6–7 d for the mutant strain. The efficiency of substrate uptake rate with respect to total volume substrate consumption rate,Q _s (g per L per h) and specific substrate consumption rate,q _s (g substrate per g cells per h) revealed that the mutant grew faster than its parent. This indicated that the selected mutant is insensitive to catabolite repression by higher concentrations of sugars for citric acid production. With respect to the product yield coefficient (Y _p/x), volume productivity (Q _p) and specific product yields (q _p), the mutant strain is significantly (p≤0.05) improved over the parental strain.