ANALYSIS OF THE RESPIRO-FERMENTATIVE GROWTH OF SACCHAROMYCES-CEREVISIAE ON GLUCOSE IN A FED-BATCH FERMENTATION STRATEGY FOR ACCURATE PARAMETER-ESTIMATION

Analysis of the respiro-fermentative growth of a strain of Saccharomyc es cerevisiae, DSM 2155 on glucose, in a simulated 5-phase feeding str ategy of fed-batch cultures executed on the Universal BIoprocess CONtr ol (UBICON) system, was carried out. There was a good agreement betwee n the estimated and the simulated values of specific growth rates. In this study, which was designed to span 0.20-0.23 h(-1) growth rates be fore returning to lower growth rates, the critical dilution rate at wh ich the switch between purely oxidative and respiro-fermentative growt h takes place was not observed. The biomass yield, specific substrate uptake and O-2 consumption rates as well as the consistency of the dat a using both carbon and available electron balances were examined. A h igh average value of true biomass energetic yield, eta(max)=0.707, and a low value of maintenance coefficient, m(e)=0.0114 h(-1), were obtai ned indicating that the organism was in no danger from the ethanol pro duced as a high-density fermentation with a yeast concentration above 54 g l(-1) was possible within a period of 24 h. The yeast produced al so had good dough-leavening characteristics. Thus it is possible to op erate a yeast plant without resorting to using respiratory quotient, w hich may be problematic, as the controlling parameter.