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Some amino acids are known to be precursors of aroma-active compounds produced by yeast metabolism. This study examined the effect of the addition of L-isoleucine and L-phenylalanine on the volatile profiles of longan wine fermented by a co-culture of Saccharomyces cerevisiae var. bayanus EC-1118 and Williopsis saturnus var. saturnus CBS254 inoculated at a ratio of 1:1 000 cfu/mL with the aim of enhancing longan wine aroma. Significantly higher concentrations of active amyl alcohol (2-methyl-1-butanol), 2-phenylethyl alcohol and their corresponding acetate esters were found in the longan wine with added L-isoleucine and L-phenylalanine respectively, compared with the control (without added amino acids). The biosynthesis of other volatile compounds was either similar or minimally different, although the formation of some acetate esters, such as isoamyl acetate, hexyl acetate and ethyl acetate, was decreased. These results suggest that the added amino acids play an important role in enhancing the production of targeted aroma compounds in longan wine fermented with mixed yeasts, and that the addition of selected amino acids can be a valuable tool to modulate the formation of aroma compounds in longan wine.

The aim of this study was to compare the chemical and volatile composition of mango wines fermented with Saccharomyces cerevisiae var. bayanus EC1118, S. cerevisiae var. chevalieri CICC1028 and S. cerevisiae var. cerevisiae MERIT.ferm. Strains EC1118 and MERIT.ferm showed similar growth patterns but strain CICC1028 grew slightly slowly. The ethanol level reached about 8% (v/v) for each mango wine and sugars (glucose, fructose and sucrose) were almost exhausted at the end of fermentation. There were only negligible changes in the concentrations of citric, succinic and tartaric acids, except for malic acid (decreased significantly). Different volatile compounds were produced, which were mainly fatty acids, alcohols and esters. Most volatiles that were present in the juice were consumed to trace amounts. The kinetic changes of volatiles were similar among the three yeasts but the concentrations of some volatiles varied with yeast. Strain MERIT.ferm produced higher amounts of higher alcohols, isoamyl and 2-phenylethyl acetates, whereas strain CICC1028 produced higher amounts of medium-chain fatty acids and ethyl esters of decanoate and dodecanoate. These results suggest that it may be possible to produce mango wines with differential characteristics using different S. cerevisiae strains.

The impact of amino acid addition on aroma compound formation in papaya wine fermented with yeast Williopsis saturnus var. mrakii NCYC2251 was studied. Time-course papaya juice fermentations were carried out using W. saturnus var. mrakii NCYC2251, with and without the addition of selected amino acids (L-leucine, L-isoleucine, L-valine and L-phenylalanine). Yeast growth and changes in sugars, °Brix, organic acids and pH were similar, regardless of amino acid addition. L-Leucine addition increased the production of isoamyl alcohol and some esters such as isoamyl acetate, isoamyl butyrate and isoamyl propionate, while L-isoleucine addition increased the production of active amyl alcohol and active amyl acetate. L-valine addition slightly increased the production of isobutyl alcohol and isobutyl acetate. L-phenylalanine addition increased the formation of 2-phenylethanol, 2-phenylethyl acetate and 2-phenylethyl butyrate, while decreasing the production of most other esters. This study suggests that papaya juice fermentation with W. saturnus var. mrakii NCYC2251 in conjunction with the addition of selected amino acid(s) can be an effective way to modulate the aroma of papaya wine.

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