Characterization of Hybrid Strains of Saccharomyces pastorianus for Desiccation Tolerance and Fermentation Performance

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dc.contributor.advisor Trevor G. Phister, Committee Member en_US
dc.contributor.advisor Todd R. Klaenhammer, Committee Member en_US
dc.contributor.advisor John D. Sheppard, Committee Chair en_US Layfield, Johnathon Blake en_US 2010-04-02T18:18:42Z 2010-04-02T18:18:42Z 2009-11-16 en_US
dc.identifier.other etd-08182009-130032 en_US
dc.description.abstract Dry yeast can be utilized in both ale and lager beer production to provide an inexpensive source of large amounts of viable cells for fermentation. This study examines the desiccation tolerance of different strains of S. pastorianus and the subsequent fermentation performance in comparison to S. cerevisiae. The use of active dry brewer’s yeast (ADY), Saccharomyces cerevisiae, as a starter for the production of ales has been gaining popularity within the brewing industry, spurring manufactures to also produce active dry lager yeast (ADLY), S. pastorianus. The drying process is known to have a greater negative effect on the cell viability and physiology of ADLY than that of ADY, possibly due to the fastidious growth, low production temperature and poor thermotolerance of S. pastorianus. This may result in lower cell viability and concentration of ADLY starter cultures, which could lead to stuck or slow fermentations. S. pastorianus is a hybrid organism resulting from a cross between S. cerevisiae and S. bayanus. It has been proposed that it can be categorized into two distinct groups: Group 1 (S. pastorianus- Saaz type) has lost a significant amount of the genomic content contained within S. cerevisiae and is therefore closer to S. bayanus; while Group 2 (S. pastorianus- Frohberg type) has retained almost all of the genomic content of S. cerevisiae. To investigate whether these two groups differ in their tolerance to desiccation, both groups of S. pastorianus were spray dried at 140oC and rehydrated in phosphate buffer at 25oC for 30 minutes. The viability of the rehydrated cultures was determined using microscopic and viable cell counts. The fermentation performance of the cultures was tested by inoculating equal counts of viable rehydrated cells into brewer’s wort and monitoring changes in cell count, carbohydrate and alcohol concentration until completion. The findings suggest that the S. pastorianus- Frohberg type is less tolerant to desiccation than either S. cerevisiae or S. pastorianus- Saaz type. The Frohberg type shows evidence of membrane damage which could delay the onset of fermentation. Utilization of the correct strain of ADLY could reduce the possibility of contamination or extended lag phases leading to stuck fermentations. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject Cellular Injury en_US
dc.subject Frohberg en_US
dc.subject Beer fermentation en_US
dc.subject Dehydration en_US
dc.subject Active dry yeast en_US
dc.subject Saccharomyces cerevisiae en_US
dc.subject Saccharomyces pastorianus en_US
dc.subject Saaz en_US
dc.title Characterization of Hybrid Strains of Saccharomyces pastorianus for Desiccation Tolerance and Fermentation Performance en_US MS en_US thesis en_US Food Science en_US

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