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

Abstract

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 50 000–63 000 (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 citric acid/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 6 g/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.