Continuous production of citric acid from raw glycerol by Yarrowia lipolytica in cell recycle cultivation

The kinetics of continuous citric acid (CA) fermentation, using two acetate-negative mutants of Yarrowia lipolytica (Wratislavia AWG7 and Wratislavia 1.31) with long-term cell recycle, were investigated at a dilution rate (D) of 0.011 h(-1). The capacity of the mutants to produce CA from raw glycerol under steady state conditions was compared. The process involving the Wratislavia AWG7 strain showed that this strain was a better producer of CA than the Wratislavia 1.31 strain in this regime. In steady state, the concentration of CA in the effluent was constant and amounted to 116 g dm(-3). This corresponded to a volumetric CA production rate of 1.3 g dm(-3) h(-1). A stable high-level production of CA was maintained for over 400 h of operation. The Wratislavia AWG7 strain employed remained highly stable throughout the experiment and demonstrated good viability, high genetic and phenotypic stability over the long-term continuous fermentation process.