Kinetics of Biphasic Growth of Yeast in Continuous and Fed-Batch Cultures

The influence of dilution rate on the production of biomass, ethanol, and invertase in an aerobic culture of Succharornyces carlsbergensis was studied in a glucoselimited chemostat culture. A kinetic model was developed to analyze the biphasic growth of yeast on both the glucose remaining and the ethanol produced in the culture. The model assumes a double effect where glucose regulates the flux of glucose catabolism (respiration and aerobic fermentation) and the ethanol utilization in yeast cells. The model could successfully demonstrate the experimental results of a chemostat culture featuring the monotonic decrease of biomass concentration with an increase of dilution rate higher than 0.2 hr-l as well as the maximum ethanol concentration at a particular dilution rate around 0.5 hr-*. Some supplementary data were collected from an ethanol-limited aerobic chemostat culture and a glucoselimited anaerobic chemostat culture to use in the model calculation. Some parametric constants of cell growth, ethanol production, and invertase formation were determined in batch cultures under aerobic and anaerobic states as summarized in a table in comparison with the chemostat data. Using the constants, a prediction of the optimal control of a glucose fed-batch yeast culture was conducted in connection with an experiment for harvesting a high yield of yeast cells with high invertase activity.