Graduate Thesis Or Dissertation
 

Gas chromatography of fermentation products of different yeast strains

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  • Many different strains of yeast have been isolated from the natural microflora on fruits. It has been known for some time that these strains of yeast have distinct fermentation characteristics and, when used in the production of wine, impart these characteristics to the wine. These characteristics may be evidenced in the flavor or aroma of the wine, the speed of the fermentation, the amount of ethanol produced and many other ways. It was reasoned that these fermentation characteristics were involved with or were a result of the metabolic system of a particular yeast strain. Since fermentation products result from the metabolic pathways, these products were studied in the hope that a better understanding of the fermentation products would lead to a better understanding of the metabolic pathways and, in turn, of the fermentation characteristics of yeast strains. The fermentations were conducted on blackberries with four strains of yeast, chosen because of their different fermentation characteristics: Saccharomyces oviformis, Saccharomyces bayanus, Saccharomyces ellipsoideus and Saccharomyces cerevisiae. Ethyl chloride was used to extract the wines after the fermentations were completed. The solvent was removed and the sample concentrated on a low temperature distillation apparatus, after which it was analyzed using gas chromatography. The gas chromatograph employed was a Wilken's Aerograph Hy-Fi with a hydrogen flame ionization detector. An eight foot X 1/8 inch stainless steel column packed with five percent Carbowax 400 on 80/100 mesh Celite 545 was used for the analyses. Peak heights were determined by measuring the recorder response (in millivolts), and the percent contribution of each peak was calculated with the greatest percent deviation within a sample being less than four percent. The initial five peaks, excluding ethanol and the solvent, accounted for approximately 99 percent of the sample and demonstrated significant differences between the yeast strains. The later peaks also aided in the differentiation although not in as pronounced a manner. A tentative identification was made, using the enrichment technique, of peaks two, three, four, five, six, seven, nine, ten, thirteen and fourteen. These were believed to be ethyl acetate, ethanol, propanol, isobutanol, butanol, isoamyl alcohol and active amyl alcohol, glycerol, 2, 3-butylene glycol or ethyl octanoate, linalool and ethyl decanoate.
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