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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2632

Title: ISOLATION AND SELECTION OF ETHANOL TOLERANT YEASTS FOR THE PRODUCTION OF ETHANOL
Authors: DECHASSA, TOLESSA KUMSA
Advisors: Dr. Dawit Abate
Keywords: Baker yeast,
biomass
Durham tube
ethanol
ethanol tolerance
optical density Spectrophotometer, sugar tolerance
Copyright: Jun-2010
Date Added: 6-May-2012
Abstract: ABSTRACT Twenty yeasts colonies were isolated from Tela, Teji, Honey and teff dough selection for ethanol tolerance on yeast extract peptone dextrose agar medium (YEPDA). All the isolates were first tested for carbohydrate fermentation using Durham tube fermentation method in yeast extract peptone dextrose broth using common fermentative carbohydrates. Ten isolates which were relatively high fermentative in Durham tube fermentation method were selected for testing of isolates for ethanol tolerance. Ethanol tolerance was tested using different concentration made from 96 %( v/v) of absolute ethanol in yeast extract peptone dextrose broth and their growth was determined by measuring optical density of the cells in broth using spectrophotometer at 615nm. Two strains of isolates showed measurable growth in medium containing above 14% (v/v) of ethanol were selected for further study. Strain TBY1 tolerates15.5% (v/v) ethanol and strain TGY2 tolerates 16% (v/v) of ethanol. Both isolates were classified under genus saccharomyces based morphological appearance of vegetative cell under microscope, ascospore production, ascospore character, colony character and physiological testing of carbohydrates using baker yeast as reference. They were found to be equally sugar tolerant having good growth in medium containing 24-28 % (w/v) sucrose. Fermentation of sucrose was optimized with respect to temperature, pH and sugar concentration. Results revealed that pH 5 and 28% sucrose concentration as optimum for fermentation for the three yeasts. The optimum temperature for selected strains and reference yeast was 300C. The maximum ethanol produced by TBY1and TGY2 from 28% of sucrose at pH 5 and temperature of 30 0C were 11.3 and 11.5% (v/v) of ethanol respectively, and 9.6%(v/v)ethanol by the standard baker’s yeast. The amount of ethanol produced in the fermentation broth was measured using ebulliometer. The biomass was determined after the end of fermentation and the result showed it the biomass of more ethanol tolerant strain is greater than the others.
URI: http://hdl.handle.net/123456789/2632
Appears in:Thesis - Biology

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