Production and Management of Aroma Compounds by

The yeast Dekkera/Brettanomyces is commonly found in wines and is responsible for a wide array of characteristic odors. The primary aim of this project is to illuminate the factors that are most important in the survival and growth of Brettanomyces bruxellensis in wine and how these factors influence the production of off odors. The role of growth in wine and defined medium on the metabolic state of Brettanomyces cells was investigated. Three strains were analyzed during growth over 54 days in wine and a defined medium. Differences in the metabolic profile were determined and correlated with each variable, strain and growth medium. Ten Brettanomyces strains for the production of odor active compounds in defined medium with specific substrates added were also analyzed. These ten strains were chosen from approximately 100 Brettanomyces strains that were screened for differences in aroma production. The ten strains were selected for lower levels of odor production both in defined medium and wine. The analysis of the metabolic profile of Brettanomyces in wine and defined medium revealed some expected differences in lipid and carbon metabolism. Unexpected differences in amino acid and nitrogen compounds were also found. Fatty acids and lipids are involved in ethanol tolerance and general stress tolerance. The changes seen in fatty acid metabolism suggest the cells are altering membrane lipids in ways designed to stabilize the membranes under stress conditions. Fatty acids such as isovaleric and isobutyric acid are also involved in off-aroma production so this adaption to stress may be correlated with off-character formation. Proline and urea were uniquely increased in wine-grown cells. The increase in these nitrogen compounds could be due their use as nitrogen sources but proline may play another role as well. Plants and bacteria use proline as an osmoprotectant. It may play a similar stabilizing role in Brettanomyces in wine. An increase in metabolic compounds involved in the use of pentose sugars was also found in wine grown cells. Differences between strains were also observed. Surprisingly there was a consistent and significant trend showing that strain UCD 2091 was different from strains UCD 2082 and UCD 2807 in multiple metabolic pathways.