REGULATORY ASPECTS OF BAKERS-YEAST METABOLISM IN AEROBIC FED-BATCH CULTURES

A highly instrumented computer-coupled bioreactor is used to investigate metabolic changes of Saccharomyces cerevisiae in aerobic fed-batch systems which are generally applied in bankers' yeast manufacture. The four types of metabolism (oxidation of glucose, aerobic fermentation, oxidation of glucose and ethanol, and oxidation of ethanol) appearing in such systems are characterized by four significant fermentation parameters: Respiratory quotient (RQ), glucose uptake rate (Qg), ethanol turnover rate (QEtOH), and growth yield on glucose (Yg). Below the critical glucose concentration glucose and ethanol are utilized simultaneously. The shift from aerobic fermentation to nondiauxic growth on glucose and ethanol is not only dependent on glucose concentration. but also on the precultivation on cells. The uptake of ethanol is controlled by the glucose supply except in the case when ethanol is limiting; the oxygen uptake rate (Qo2), however, is unaffected by the ratio of Qg and QEtOH. Critical glucose concentration is not a constant value for a particular strain, but varies corresponding to the nutritional state of the cells. © 1981 John Wiley & Sons, Inc.