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Förslaget inkom 2008-05-06

Simultaneous starch saccharification and yeast biomass production

MicroDrivE – MSc Project School
Environmental and economic reasons motivate focused research on biofuel production. The new research programme MicroDrivE – Microbially Derived Energy, offers a series of MSc projects within bio-preservation, enzymatic pre-treatments, ethanol fermentation, bioprocessing of byproducts, biogas production and fertility effects of bioresidues. The projects are supervised by scientists from the Departments of Microbiology, Molecular Biology, and Chemistry at the Swedish University of Agricultural Sciences (SLU), Uppsala. MicroDrivE cooperates with a number of biotech and bioenergy companies. For information on the other MSc projects use the search function ”Fritext” to search for MicroDrive.

Background and goal
Starch containing materials are attractive substrates for the production of bakers’ yeast, because they are cheap and available in large amounts. However, because yeast cannot degrade starch, an enzymatic degradation of the starch is necessary before the fermentation. This two-step procedure requires a substantial investment into the technology, as separate fermenters are needed for substrate degradation and yeast growth. Moreover, bakers’ yeast tends to repress respiration and to perform the energetically less efficient ethanol fermentation when the sugar concentration is high. Thus, a sophisticated feeding strategy must be applied, to avoid the increase of free fermentable sugars in the fermentation. If a process can be developed where starch is degraded directly inside the yeast production fermenter, the demands for investments and feeding regulation may be substantially decreased.
In a first step, we will test the ability of several commercially available enzymes to degrade soluble starch, with special consideration of the degradation velocity at conditions at which bakers’ yeast can grow (30-32ºC, pH 5-6). Based on these results, a model cultivation (based on a simple shake-flask culture) will be established, where bakers’ yeast is grown in the presence of starch and the starch degrading enzymes with the highest degradation capacity. We will estimate the basic growth parameters, like specific growth rates, biomass yields and maximum final biomass concentration dependent on the amount of substrate and added enzyme.

• Cultivation of yeast, strain conservation
• Measurement of enzyme activities
• Determination of growth parameters, biomass determination, sugar, ethanol quantification by HPLC

We are looking for a student within the microbiology and biotechnology area interested in future technologies for biofuel production and environmental concerns.

For information on the Department of Microbiology, SLU, visit our Web-site: http://www.mikrob.slu.se


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