Dynamics of volatile compounds during longan juice fermentation by three yeasts from the genusWilliopsis

Three yeasts from the genus Williopsis (W. saturnus var. mrakii NCYC500, W. saturnus var. saturnus CBS254 and W. californica NCYC2590) were examined for their ability to ferment longan juice and to enhance formation of longan wine aroma compounds. The three yeasts showed similar growth kinetics and pH changes during fermentation. W. californica was the least sugar consumer. Many of the naturally occurring volatiles (ethyl esters, fatty acids, aldehydes, and terpenes) in the juice were partially or completely degraded. The three yeasts varied with their ability to produce and utilise volatiles. Esters were the major volatiles produced with some esters being catabolised while other esters remained stable. The amount of most alcohols increased while of aldehydes decreased. W. saturnus CBS254 was the best producer of ethyl acetate, isobutyl acetate, isoamyl acetate and 2-phenethyl acetate, whereas W. californica NCYC2590 was the highest producer of butyl acetate. Ethanol was produced in similar amounts by W. mrakii and W. saturnus but at a minimal level by W. californica. W. mrakii formed the highest amount of isobutyl alcohol, isoamyl alcohol and 2-phenylethyl alcohol. Although the amounts of most of the major volatiles at the end of fermentation (day 14) differed statistically among the yeasts, it remained to be seen whether the quantitative differences can be detected organoleptically. These fi ndings suggest that yeasts from the genus Williopsis could be exploited for longan wine aroma enhancement either singly or in co-inoculation with Saccharomyces.