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

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. Le transport des acides amines a chaine ramifiee est important en brasserie, specialement parce que les metabolites de ces composes sont convertis en alcools superieurs qui sont en grande partie responsables de la flaveur dans les boissons alcoolisees. L'addition de valine, d'isoleucine et de leucine dans le mout provoque une augmentation de la production de l'alcool superieur correspondant suggerant que cette production est liee a l'assimilation de l'acide amine correspondant. Par expression constitutive du gene BAP2 dans la levure de brasserie, cette recherche etudie les effets sur l'assimilation d'acides amines a chaine ramifiee et la production d'alcools superieurs pendant la fermentation. Les resultats suggerent qu'il existe des mecanismes distincts mais lies entre eux pour la production de chaque alcool superieur.