The yeast Dekkera/Brettanomyces is commonly found in wines and is responsible for a wide array of characteristic odors. The aim of this project is to define the role of substrate availability and physical growth factors in production of desired and undesired aroma compounds. A practical aim is to determine the impact of nutrients on growth and off odor production by Brettanomyces. We attempted to determine if the growth of Brettanomyces and the production of off odors can be controlled by controlling nutrients.
To this end we have looked at egg white fining as a means of controlling vitamin availability in wine. We are in the process of doing a descriptive analysis of egg white fining trials in wine. The isolates of Brettanomyces were also grown in a defined medium supplemented with aromatic amino acids or phenolic compounds to determine what substrates might produce specific aroma associated chemical compounds. Initially we looked at the compounds that were common to most of the five strains that were grown with the added substrates as well as those that are substrate specific. Now we have looked at the strain specific compounds as well.
In a defined medium the range of aroma-associated compounds produced by Brettanomyces was very broad. The variety of compounds produced by the Brettanomyces strains without supplementation included many of the same aroma compounds associated with Saccharomyces. The compounds produced specifically in the defined medium supplemented with the amino acids and organic acids belonged to several different classes. We found higher alcohols, fatty acids and their esters, volatile phenols, terpenes, and an aldehyde and a carboxylic acid. The volatile phenols were associated with the organic acid supplements while the fatty acids and their esters were primarily associated with amino acid supplements. Certain strains seem to be using specific substrates preferentially to produce aroma compounds. The use of these compounds may be correlated with regeneration of reducing power and could be connected to preferred metabolic pathways.
We have grown three Brettanomyces bruxellensis strains under three levels of oxygen, 0, 25, and 50%air saturation. Results indicate that there is some production of 4-ethylphenol (4-EP) from coumaric acid even under 0%air when growth is severely limited. Results indicate that growth under low oxygen is enhanced by the presence of coumaric acid in strain 2077 at 25%air saturation, in strain 2091 at 50%air saturation, and in strain 2082 at both 25%and 50%air saturation. These results are again consistent with the use of coumaric acid conversion to 4-ethylphenol to regenerate reductant under low oxygen conditions.