Effect of amino acid supply on the transcription of flavour-related genes and aroma compound production during lager yeast fermentation

The objective of this study was to investigate the effect of adding selected amino acids (proline, leucine, cysteine, valine, glutamine and isoleucine) to synthetic wort on the generation of aroma compounds with respect to the transcription levels of specific genes involved in their biosynthetic pathway under brewery fermentation. The results showed that the changes in the selected amino acid levels had no eminent impact on the general course of fermentation. Addition of leucine increased the production of isoamyl alcohol and isoamyl acetate and 2-methylbutyl acetate. Adding valine and isoleucine increased the production of isobutanol and 2-methyl butanol, respectively. Overall, total higher alcohol production increased by amino acid supplementation; this effect could be associated with the upregulation of pyruvate decarboxylases and phenylpyruvate decarboxylase. Amino acid supplementation resulted in a reduction in the final total concentration of esters, especially ethyl acetate. This reduction might have been caused by the downregulation of the genes participating in ester biosynthesis. Our results demonstrate that during lager yeast fermentation, the production of aroma-active compounds can be significantly affected by changing the supply of even one amino acid.