Control of higher alcohol production by manipulation of the BAP2 gene in brewing yeast

We studied whether the production of higher alcohols during wort fermentati on is responsive to branched-chain amino acid metabolism. Addition of valin e, isoleucine, and leucine to the brewing wort resulted in increased assimi lation of each amino acid by yeast cells and caused increased production of the corresponding higher alcohol, suggesting that production of a higher a lcohol is correlated with the assimilation of the corresponding amino acid. Therefore, we attempted the constitutive expression of the gene (BAP2) for the branched-chain amino acid permease in brewing yeast and investigated t he effects on assimilation of branched-chain amino acids and production of higher alcohols daring wort fermentation. Constitutive expression of the BA P2 gene resulted in accelerated rates of assimilation for leucine, valine, and isoleucine. This caused increased production of isoamyl alcohol derived from leucine, while an increase of isobutyl alcohol derived from valine or active amyl alcohol from isoleucine was not observed. These results sugges t that there are distinct but interrelated mechanisms for the production of each higher alcohol.