Fed-batch production of citric acid by Candida lipolytica grown on n-paraffins.

This study reports on the effects of fermentor agitation and fed-batch mode of operation on citric acid production from Candida lipolytica using n-paraffin as the carbon source. An optimum range of agitation speeds in the 800-1000 rpm range corresponding to Reynolds numbers of 50000-63000 (based on initial batch conditions) seemed to give the best balance between substrate utilization for biomass growth and citric acid production. Application of multiple fed-batch feedings can be used to extend the batch fermentation and increase final citric acid concentrations and product yield. The three-cycle fed-batch system increased overall citric acid yields to 0.8-1.0 g citricacid/g n-paraffin, approximately a 100% improvement in product yield from those observed in the single cycle fed-batch system and a 200% improvement over normal batch operation. The three-cycle fed-batch mode of operation also increased the final citric acid concentration to 42 g/l from about 12 and 6g/l for single fed-batch cycle and normal batch modes of operation, respectively. Increased citric acid concentrations in three-cycle fed-batch mode was achieved at longer fermentation times.