Effect of the addition of branched-chain amino acids to non-limited nitrogen synthetic grape must on volatile compounds and global gene expression during alcoholic fermentation

Background and Aims: The concentration and composition of nitrogen (N) in must is critical to yeast fermentation and aroma profiles in wine. We investigated the effect of adding branched-chain amino acids (BCAAs, including L-valine, Lleucine and L-isoleucine) to a non-limited N medium on the formation of aromatic compounds and on gene expression patterns of the wine yeast Saccharomyces cerevisiae. Methods and Results: A synthetic N-sufficient must was supplemented with BCAAs and fermented with S. cerevisiae. The fermentation kinetics, aroma characteristics and yeast global gene expression in wine with addition of BCAAs were compared with that of the Control. Addition of BCAAs improved yeast growth and fermentation activity, increased the production of higher alcohols, medium-chain fatty acids and their corresponding esters (82, 34 and 49% increment compared to that of the Control, respectively). The comparative transcriptomic analysis revealed that 25 genes varied in their expression during fermentation with added BCAAs relative to that of the Control, which are mainly involved in yeast growth and proliferation (GIP1, DIT2, RCK1, SPO1 and MEK1) and transport of amino acids (GAP1). Conclusions: An increase in BCAA transport ability and in yeast population is the main reason for achieving an increased concentration of volatile aroma compounds in wine with addition of BCAAs. Significance of the Study: Our results suggest that adding BCAAs into N-sufficient must is still an efficient way to adjust wine's aromatic composition and improve aroma complexity.