African Journal of Biotechnology Vol.. 2 (5), pp. 96-103, May 2003    

ISSN 1684-5315  © 2003 Academic Journals

Substrate Channelling and Energetics of Saccharomyces cerevisiae DSM 2155 Grown on Glucose in Fed-Batch Fermentation Process

Olusegun Peter Akinyemi¹, Eriola Betiku^2+*, and Bamidele Ogbe Solomon²

¹Chemical and Polymer Engineering Department, Lagos State University, Lagos State, Nigeria.

²Chemical Engineering Department, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.

*Corresponding author: E-mail: erb@gbf.de, Tel.: +49-531-6181-183, Fax:  +49-531-6181-111

⁺Present address: German Research Centre for Biotechnology, Biochemical Engineering Division, Mascheroder Weg 1, D-38124, Braunschweig, Germany

Accepted 10 April, 2003.

Data collected during the 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, m_e = 0.004h^-1, and a high average value of the true biomass energetic yield,  h_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 (q_sresp/q_s) 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.

Key Words: Saccharomyces cerevisiae DSM 2155, available electron and carbon balances, fed-batch, respiratory quotient, true energetic yields, maintenance requirement.