Christian Paumi (1), Dylan Fugate (1), Matt Linske (2), Tim Schwarze (1); (1) Eastern Kentucky University, Richmond, KY, U.S.A.; (2) Brewing and Distilling Analytical Services, Lexington, KY, U.S.A.

Yeast, Fermentation, and Microbiology

Over the last 5-10 years a number of groups interested in decreasing free radicals during the fermentation and bottling processes of beers and wines have examined mechanisms to increase GSH content and excretion by yeast during the fermentation process. These studies have utilized classical and modern genetics to increase GSH content via increasing the GSH synthesis proteins Gsh1p and Gsh2p. The initial studies indicate that increasing yeast GSH cellular content and GSH excretion does increase the antioxidant capacity of the must and wort, while also increasing the stability of beer and wine flavor post-bottling. Further, a recent study published in 2014 examining Gpx1p and catalase (Cttp1p) mediated protection against oxidative stress supports the role of glutathione as an important protective antioxidant in yeast during fermentation. Elevated levels and activity of Gpx1p and Ctt1p contribute to elevated cellular and extracellular GSH. Together these studies suggest an important role for the antioxidant glutathione-based system in protecting yeast from oxidative stress during fermentation and for a role for GSH as a natural preservative that protects beverages from oxidation. However, it is important to note that GSH is in equilibrium with GSSG and that this delicate balance is maintained via a complex multi-protein system containing the GSH synthesis proteins Gsh1p and Gsh2p, glutathione reductase (Glr1p), and glutathione-utilizing and -linked proteins such as glutathione peroxidase (Gpx1p, Gpx2p, and Gpx3p), Ctt1p, and superoxide dismutase (Sod1p and Sod2p). To date no lab has examined how these systems work together to regulate oxidative stress during fermentation and regulate oxidation in bottled beer and wine. Our lab has utilized classical genetic approaches and the yeast deletion collection to increase the GSH content of a standard laboratory strain of Saccharomyces cerevisiae (BY4741 background). As the organic components of beer and wine play a critical role in product quality, stability, and sensory profiles, we have monitored a small number of select compounds throughout the fermentation processes via headspace GC analysis. In addition we have measured and compared fermentation efficiency in each of the deletion and control strains. Oxidative stress was measured as a function of DCFDA fluorescence, a measure of general reactive oxygen species. The flavor compound profile and DCFDA results were then compared to measured levels of GSH. Ultimately, we hope that by exposing yeast brewing strains to an oxidant inducer, our lab will selectively induce genes involved in GSH synthesis and recycling for use in the brewing industry.

Christian Paumi is an assistant professor of fermentation microbiology at Eastern Kentucky University in the Department of Chemistry and is a faculty member in the Fermentation Science program. As a recent addition to the Department of Chemistry, Christian has been involved in the establishment of the new Fermentation Science program, including teaching Fermentation Microbiology. Prior to joining EKU, Christian was an assistant professor in the Graduate Center for Toxicology (GCT) at the University of Kentucky (UKY). Prior to his position at the University of Kentucky, Christian did his postdoctoral fellowship at Johns Hopkins University in the Department of Cell Biology (Baltimore, MD) and obtained his Ph.D. degree in biochemistry and molecular biology from Wake Forest University in the Department of Biochemistry and Molecular Biology. Christian is a member of the newly formed East Coast-Midwest Alcohol Beverage Initiative Group and actively collaborates with Brewing and Distilling Analytical Services and Ferm Solutions of Kentucky.