CITRIC-ACID PRODUCTION BY CANDIDA-LIPOLYTICA Y-1095 IN CELL RECYCLE AND FED-BATCH FERMENTERS

The effect of dissolved oxygen on citric acid production and oxygen up take by Candida lipolytica Y 1095 was evaluated in cell recycle and fe d-batch fermentation systems. The maximum observed volumetric producti vity, which occurred at a dilution rate of 0.06 h(-1), a dissolved oxy gen concentration of 80%, and a biomass concentration of 5% w/v, in th e cell recycle system, was 1.32 g citric acid/L . h. At these same con ditions, the citric acid yield was 0.65 g/g and the specific citric ac id productivity was 24.9 mg citric acid/g cell h. In the cell recycle system, citric acid yields ranged from 0.45 to 0.72 g/g. Both the volu metric and specific citric acid productivities were dependent on the d ilution rate and the concentration of dissolved oxygen in the fermente r. Similar productivities (1.29 g citric acid/L . h) were obtained in the fed-batch system operated at a cycle time of 36 h, a dissolved oxy gen concentration of 80%, and 60 g total biomass. Citric acid yields i n the fed-batch fermenter were consistently lower than those obtained in the cell recycle system and ranged from 0.40 to 0.59 g/g. Although citric acid yields in the fed-batch fermenter were lower than those ob tained in the cell recycle system, higher citric:isocitric acid ratios were obtained in the fed-batch fermenter. As in the cell recycle syst em, both the volumetric and specific citric acid productivities in the fed-batch fermenter were dependent on the cycle time and dissolved ox ygen concentration. (C) 1995 John Wiley and Sons, Inc.