The synergistic influences of three unsaturated fatty acids (UFAs, namely linoleic acid, oleic acid and linolenic acid) on the fatty acid composition of Saccharomyces cerevisiae and major volatile compounds were investigated in synthetic grape juice. The addition of UFAs led to a corresponding increase in UFAs in the cellular lipid, which was accompanied by a reverse reduction in the content of medium-chain saturated fatty acids (C6:0 to C14:0) and little variation in that of long-chain saturated fatty acids (C16:0 to C24:0). The supplementation of UFAs considerably improved yeast growth and fermentation activity and, in particular, increased the concentrations of most volatile compounds in wine, including higher alcohols (2-phenylethanol, 2-methyl-1-propanol and 3-(methylthio)-1-propanol), medium-chain fatty acids (butanoic acid, hexanoic acid and octanoic acid), acetate esters (isoamyl acetate and 2-phenylethyl acetate) and all ethyl esters. Remarkable linear relationships were further found between ethyl esters and the concentration of the added UFAs (R 2 from 0.909 to 0.996), which significantly intensified the fruity, flowery and sweet attributes of the final wine, as assessed by calculating the odour activity values. Our results suggest that rationally increasing the concentration of UFAs is not only a practical method to improve yeast fermentation activity, but also a potential approach to manipulating wine aroma.

The effects of adding branched-chain amino acids (BCAAs, including L-valine, L-leucine and L-isoleucine), L-phenylalanine and a mixture of them (BCAAs + Phe) on the fermentation profiles of wine yeast EC1118 and the production of volatile compounds were investigated in synthetic grape juice. The addition of selected amino acids had no considerable influence on the yeast growth and primary metabolites of the sugars. Adding BCAAs increased the production of higher alcohols, medium-chain fatty acids (MCFAs) and their corresponding ethyl esters. In comparison, adding Phe promoted the production of 2-phenylethanol, 2-phenylethyl acetate and ethyl esters of MCFAs. Nevertheless, the supplementation of BCAAs + Phe further heightened the production of MCFAs, acetate esters and ethyl esters of MCFAs compared to the single additions, but it attenuated the production of various higher alcohols (1-propanol, 2,3-butanediol and methionol) compared to the addition of BCAAs, and of 2-phenylethanol and 2-phenylethyl acetate contents compared to the Phe addition. These results suggest that adding BCAAs or Phe is an efficient way to adjust wine's aromatic composition and complexity. Meanwhile, the combined addition of BCAAs + Phe could be a potential tool to further manipulate wine's aromatic profile by accentuating or suppressing the formation of certain aroma compounds.