Fermentation systems for enhancement of ethanol productivity in Saccharomyces cerevisiae at elevated temperatures
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Three Brazilian yeast strains, Saccharomyces cerevisiae 42 - F, Saccharomyces cereviaiae PLA 851 and Saccharomyces boulardli IZ 1904, all currently employed in the sugar fermentation industry, were evaluated with respect to their thermal tolerance and alcohol production kinetics. Best performance was found in Saccharomyces cerevisiae PLA 851 at temperatures up to 40 degrees (a common fermentation temperature in the Brazilian industry). This strain was further evaluated in chemostatic growth under sucrose limitation with biomass feedback on a 1 Litre scale in a specially constructed apparatus. At 30 degrees and 35 degrees under a dilution (growth) rate of 0.1 /h ethanol productivity increased by a factor of 2 with feedback and at 40 degrees by a factor of 3. The feedback factor (Beta) was 0.9. PLA 851 cells, heat - shocked at 45 degrees, resulted in a greater biomass productivity subsequently at 40 degrees coupled with a change in cell morphology. Highest ethanol productivity was found with 10% initial sucrose concentration at a dilution rate of 0.25 /h with feedback. Saccharomyces cerevisiae PLA 851 appears to be well adapted to the harsh physiological conditions in alcohol fermentations as currently practiced in Brazil.
Thesis, PhD Doctor of Philosophy
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