Control of Higher Alcohol Production by Manipulation of the <i>BAP2</i> Gene in Brewing Yeast

Abstract

We studied whether the production of higher alcohols during wort fermentation is responsive to branched-chain amino acid metabolism. Addition of valine, isoleucine, and leucine to the brewing wort resulted in increased assimilation of each amino acid by yeast cells and caused increased production of the corresponding higher alcohol, suggesting that production of a higher alcohol 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 the effects on assimilation of branched-chain amino acids and production of higher alcohols during wort fermentation. Constitutive expression of the BAP2 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 suggest that there are distinct but interrelated mechanisms for the production of each higher alcohol.