OXYGEN-UPTAKE AND CITRIC-ACID PRODUCTION BY CANDIDA LIPOLYTICA-Y 1095

The rates of oxygen uptake and oxygen transfer during cell growth and citric acid production by Candida lipolytica Y 1095 were determined. T he maximum cell growth rate, 1.43 g cell/L . h, and volumetric oxygen uptake rate, 343 Mg 02/L . h, occurred approximately 21 to 22 h after inoculation. At the time of maximum oxygen uptake, the biomass concent ration was 1.3% w/v and the specific oxygen uptake rate was slightly g reater than 26 Mg 02/g cell . h. The specific oxygen uptake rate decre ased to approximately 3 mg 02/g Cell . h by the end of the growth phas e. During citric acid production, as the concentration of dissolved ox ygen was increased from 20% to 80% saturation, the specific oxygen upt ake and specific citric acid productivity (mg citric acid/g cell . h) increased by 160% and 71%, respectively, at a biomass concentration of 3% w/v. At a biomass concentration of 5% w/v, the specific oxygen upt ake and specific citric acid productivity increased by 230% and 82%, r espectively, over the same range of dissolved oxygen concentrations. T he effect of dissolved oxygen on citric acid yields and productivities was also determined. Citric acid yields appeared to be independent of dissolved oxygen concentration during the initial production phase; h owever, volumetric productivity (g citric acid/L.h) increased sharply with an increase in dissolved oxygen. During the second or subsequent production phase, citric acid yields increased by approximately 50%, b ut productivities decreased by roughly the same percentage due to a lo ss of cell viability under prolonged nitrogen-deficient conditions. (C ) 1994 John Wiley & Sons, Inc.