Citric acid production by Aspergillus niger immobilized on cellulose microfibrils: influence of morphology and fermenter conditions on productivity

Continuous and batch production of citric acid from sucrose has been invest igated using Aspergillus niger NCIM 588. Mycelia of A. niger grown on cellu lose microfibril forms a uniform and thin mycelial proliferation under cont rolled conditions of cultivation rich in oxygen. In the fed batch mode usin g a recycle reactor, the DO of the system was maintained at 20 mg l(-1) usi ng oxygen enriched air. This improved volumetric productivity to 1.85 g l(- 1) h(-1) of citric acid, representing an increase of at least 15-fold over results obtained simultaneously using shake-flasks and 1.6-fold over a conv entional aerated batch reactor. It was possible to substitute sucrose with sugarcane juice as a carbon source in a fed batch recycle system. An overal l specific production rate of citric acid of 0.147 and 0.208 g g(-1) h(-1) was achieved using cane juice and sucrose, respectively. In continuous ferm entation, a medium containing 50 g l(-1) of sucrose was allowed to drip thr ough the fabric support at a residence time of 20 h. As a result of interfa ce interaction, a citric acid volumetric productivity of 2.08 g l(-1) h(-1) was achieved for 26 days without any significant loss of productivity. (C) 2001 Elsevier Science Ltd. All rights reserved.