Subthreshold Vicinal Diketone Levels in Lager Brewing Yeast Fermentations by Means of ILV5 Gene Amplification¹

1 Presented at the 55th Annual Meeting, Denver, CO, April 1989.

Abstract

Previous work on the haploid yeast Saccharomyces cerevisiae has demonstrated the positive role that ILV5 gene amplification plays in reducing vicinal diketone (VDK) levels in fermentations. The present work followed the same approach toward VDK reduction by amplification of the ILV5 gene product reductoisomerase in the lager brewing yeast Saccharomyces uvarum. The ILV5 gene was cloned into a 2μm-based plasmid using copper resistance as a selectable marker. Transformation and subsequent fermentations using European Brewing Convention tubes showed an increase in reductoisomerase activity and a 70–80% decrease in VDK levels throughout the course of the fermentations. Data collected also showed that fermentation capacity levels, growth rates, and flavor profiles were unaffected by increased ILV5 gene dosage.

• Amino acid
• Isoleucine
• Reductoisomerase
• Valine
• Vicinal diketone