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

Abstract

Continuous and batch production of citric acid from sucrose has been investigated using Aspergillus niger NCIM 588. Mycelia of A. niger grown on cellulose microfibril forms a uniform and thin mycelial proliferation under controlled conditions of cultivation rich in oxygen. In the fed batch mode using a recycle reactor, the DO of the system was maintained at 20 mg l^-1 using 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 conventional aerated batch reactor. It was possible to substitute sucrose with sugarcane juice as a carbon source in a fed batch recycle system. An overall 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 fermentation, a medium containing 50 g l^-1 of sucrose was allowed to drip through the fabric support at a residence time of 20 h. As a result of interface 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.