Differential transcribed yeast genes involved in flavour formation and its associated amino acid metabolism during brewery fermentation

During fermentation, Saccharomyces yeast produces various aroma-active metabolites which determine the different characteristics of aroma and taste in fermented beverages. Amino acid utilisation by yeast during brewer's wort fermentation is considered to be linked to flavour profile. For a better understanding of the relationship between the biosynthesis of aroma-relevant metabolites and the importance of amino acids, DNA microarrays were carried out on the Saccharomyces cerevisiae strain S81 and the Saccharomyces pastorianus strain S23. Changes in the transcription of those genes were measured which are associated with amino acid assimilation and its derived aroma-active compounds during fermentation. Genes were selected whose average expression level increased or decreased more than 1.5-fold at 8, 12, 24, 48, 72, 96 or 120 h and showed a significant (P a parts per thousand currency sign 0.05) differential expression pattern during the period of fermentation. For the ale strain, 57 of the detected genes involved in flavour and amino acid metabolism were selected, whereas 46 significant genes were evaluated for the lager strain. Among these, genes were those involved in transcriptional regulation as well as others associated with amino acid transport, such as PUT4 which is accountable for the uptake of proline. Other genes whose expression decreased or increased during fermentation were evaluated-including those participating in amino acid metabolism, for example glutamate and proline metabolism-as well as enzymes involved in the biosynthesis of aroma-active higher alcohols and esters, which are most important for typical beer flavour. This study provides information that might help to improve the understanding and production of defined concentrations of specific aroma compounds during brewery fermentation.