Abstract
Data collected during high-cell-density cultivation of Saccharomyces cerevisiae DSM 2155 on glucose in a simulated five-phase feeding strategy of fed-batch process, executed on the Universal BIoprocess CONtrol (UBICON) system using 150L bioreactor over a period of 24h have been analysed. The consistency of the data set was checked using both the available electron and carbon balances. Estimates of the true energetic yields and cell maintenance requirements were obtained through the application of a multivariate statistical procedure known as covariate adjustment technique. A low value of maintenance coefficient, me = 0.004h -1 , and a high average value of the true biomass energetic yield, max = 0.745, were obtained for the bioreactor system, which showed that the organism was in no danger of ethanol produced during this cultivation. A simple model for estimating the distribution of substrate consumed between the fermentative and the respiratory pathways in the oxido-reductive process was developed based on the respiratory quotient (RQ) values. The fraction of substrate consumed for respiratory metabolic activities (qsresp/qs) was virtually 1.0 for the first three phases of the feeding strategy, which accounted for the first sixteen hours of the 24h operation. This was an indication that ethanol formation was avoided during this period.
Highlights
In recent years, baker’s yeast (Saccharomyces cerevisiae), considered the most intensively cultivated and commercial microorganism, has been used extensively for the production of single-cell protein (SCP) for human and animal consumption, and ethanol from fermentable sugars because of its GRAS (Generally Regarded As Safe) status (Solomon et al, 1997)
The low productivity obtained under both aerobic batch cultivation and during continuous cultures as a result of dilution rate dependence has led to the adoption of fed-batch process for baker’s yeast production (Beudeker et al, 1990; Ejiofor et al, 1994a,b)
These observations have been attributed to the Crabtree effect or glucose effect (Barford and Hall, 1979; Beck and von Meyenburg, 1968; De Deken, 1966; Fiechter and Seghezzi, 1992; Pronk et al, 1996)
Summary
Baker’s yeast (Saccharomyces cerevisiae), considered the most intensively cultivated and commercial microorganism, has been used extensively for the production of single-cell protein (SCP) for human and animal consumption, and ethanol (industrial and potable alcohol) from fermentable sugars because of its GRAS (Generally Regarded As Safe) status (Solomon et al, 1997) It is widely used in leavening of dough because of its ability to produce carbon dioxide and ethanol from sugars (i.e. maltose and sucrose) present in the dough (Chen and Chiger, 1985; Jørgensen et al, 2002; Reed and Nagodawithana, 1991). The derived model for substrate partitioning into the two pathways could be used along side with other growth parameters like true biomass energetic yield, true product energetic yield and maintenance requirement for cell growth as controlling parameters when operating a baker’s yeast plant
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