Analysis and metabolic acclimatization of active dry yeast for the fuel ethanol industry

The focus of this thesis was to examine the relatedness of industrially available active dry yeast (ADY) and to examine the method of "yeast propagation" used for the production of fuel ethanol. A new term, metabolic acclimatization; abbreviated as MAcc, was proposed to describe this process. Nutritional improvements and how this affects "yeast propagation" and subsequent fermentations were also investigated.; Seven industrial ADY obtained from different suppliers were subjected to traditional screening methods (viability, contaminant levels, fermentation rates, generation times, size analysis, optimal fermentation temperature, fermentative performance in normal and very high gravity corn mashes). They were also compared using molecular techniques (karyotyping and mitochondrial DNA analysis). Results of the traditional screening techniques allowed each ADY to be characterized and compared. For example, it was observed that of the seven samples, one had a low viability compared to the expected norm of ∼2.2 x 110 cells/g. Two of the samples were observed to have high levels of contaminants (0.1% anaerobic bacteria) suggesting that these samples should not be used due to the risk of bacterial contamination and subsequent loss of ethanol yield during fermentation. The differences seen in activity were probably due to manufacturing processes and drying techniques. Molecular examination of the seven ADY samples revealed four distinct karyotypic patterns. Mitochondrial DNA (mtDNA) analysis confirmed the karyotypic results (with the exception of one ADY) and revealed that only three distinct patterns could be seen. These results demonstrated that of the seven ADY, only one sample was unique as the other six (in two Groups) were found to share karyotypic and mtDNA patterns. This would suggest that most of the industrially available ADY share their lineage with other marketed yeasts, and as few as three yeasts may be available to industry but produced by more than one company. (Abstract shortened by UMI.)...