A fuzzy logic controller to control nutrient dosage in a fed-batch baker's yeast process
A fuzzy logic controller designed to control glucose feeding in a fed-batch baker's yeast process is presented. Feeding is carried out in portions and the controller determines the time at which glucose should be added and computes the size of the portion to provide the maximum glucose uptake rate. Moreover, the controller detects and prevents the occurrence of overdosage. The experimental results indicate that yield and specific growth rate obtained with the controller approached 55% and 0.13 h−1, respectively.
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.
An adaptive on-line control feed rate system in a laboratory scale bakers yeast process
SummaryA new control policy for the on-line optimization of the nutrient supply in bakers yeast process is proposed. A feed rate corresponding to minimal substrate uptake time was shown to be optimal for cell yield and specific growth rate. Cultivation results of baker's yeast are presented.