Oxygen requirements for d-xylose fermentation to ethanol and polyols by Pachysolen tannophilus |
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Authors: | Nan E. Watson Bernard A. Prior James C. du Preez Pieter M. Lategan |
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Affiliation: | Department of Microbiology, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, South Africa |
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Abstract: | The oxygen requirements for ethanol production from d-xylose (10 or 20 g l?1) by Pachysolen tannophilus have been determined by controlling the availability of oxygen to shake flasks. Under anaerobic conditions no ethanol was produced whereas under aerobic conditions mainly biomass was formed. Semi-anaerobic conditions resulted in maximum ethanol production. By varying the stirring speed of a fermenter and supplying air to the liquid surface at various rates, the oxygen transfer rate (OTR) was controlled under semi-anaerobic conditions. By increasing the OTR from 0.05 to 16.04 mmol l?1 h?1, the ethanol yield coefficient decreased from 0.28 to 0.18 while the cell yield coefficient increased from 0.14 to 0.22. The accumulation of polyols decreased from 0.88 to 0.56 g l?1 with increasing OTR. At OTRs between 0.09 and 1.18 mmol l?1 h?1, specific ethanol productivity attained a maximum value of 0.07 h?1 and decreased with either increasing or decreasing OTR. The results indicate that the OTR must be carefully controlled for efficient ethanol production from d-xylose by P. tannophilus. |
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Keywords: | oxygen requirement ethanol polyols To whom correspondence should be addressed. |
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