Transcriptional profiling of amino acid supplementation and impact on aroma production in a lager yeast fermentation

Abstract

The objective of this study was to investigate the effect of adding selected amino acids (glutamate, proline, lysine and valine) to brewing wort on the generation of aroma active compounds along with the transcriptional profiling of genes involved in nitrogen regulation. The results showed that changes in the amino acid levels had no significant impact on the general course of fermentation except for the addition of lysine, which prolonged the period that lager yeast was in suspension. Flavour profile of lager were significantly affected by valine addition, which improved the degree of fermentation and alcohol concentration. Changes in the amount of isoamyl alcohol caused by varied amino acid conditions were particularly important as it fluctuated across the flavour threshold. Amino acid supplementation resulted in a reduction in yeast total amino acid utilisation except for valine. Furthermore, we found that nitrogen regulation genes were differentially expressed according to the amino acid added and stage of yeast growth, demonstrating that divergent mechanisms and pathways are involved in transcriptional regulation down-regulating activators or up-regulating repressors of nitrogen catabolite repression pathway at the mid-exponential stage. An enexpected expression of genes related to SPS sensing system and the TOR pathway was found during the late exponential stage. Overall, our results indicate that, during lager yeast fermentation, the production of aroma active compounds and nitrogen regulation can be significantly affected by changing wort amino acid composition. © 2018 The Institute of Brewing & Distilling.