Qualitative abundance of volatile esters in Malvazija istarska white wine as revealed by comprehensive two-dimensional gas chromatography: effect of non-Saccharomyces yeasts

Yeasts from the genus Saccharomyces are most commonly used in wine production. On the other hand, in the last years there is a growing interest in use of non-Saccharomyces yeasts for reducing the content of ethanol, modifying acidity, improving protein stability, and enhancing wine aroma. In this experiment, grape must of Malvazija istarska was inoculated with five commercial non-Saccharomyces yeasts and a Saccharomyces cerevisiae/Saccharomyces paradoxus hybrid with the aim to investigate the effect of yeast on the content of volatile esters, key compounds that determine wine aroma and flavour. Saccharomyces cerevisiae was inoculated at 1.5-2.0 % (v/v) of ethanol to finish fermentations and was also inoculated in monoculture as a control treatment. Ester profiles were analysed by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOF- MS) combined with conventional mono-dimensional GC–MS. More than a hundred esters were identified or tentatively identified, providing one of the most detailed profiles of volatile esters in wine in general. Torulospora delbrueckii showed the highest potential to produce ethyl isobutyrate, isopropyl, isoamyl, 2-phenethyl, and geranyl acetates, ethyl 3-hexenoate, and ethyl 4- hexanoate. Pichia kluyveri produced most trans-3- hexenyl acetate, ethyl 2-methylbutyrate, and ethyl 3-methylbutyrate, Metschnikowia pulcherrima produced the highest amounts of ethyl decanoate and ethyl phenyl lactate, S. cerevisiae/paradoxus hybrid excelled in the production of 2-phenethyl isobutyrate and ethyl benzeneacetate, while Lachancea thermotolerans wine was the most abundant in isobutyl octanoate. Schizosaccharomyces pombe treatment wine was characterized by elevated concentrations of particular esters not commonly reported in wine aroma studies, such as esters of isoamyl alcohol with propanoic, isobutyric, isovaleric, lactic, and succinic acid, esters of 2-phenylethanol with formic, propanoic, isovaleric, hexanoic, and octanoic acid, as well as S-ethyl octanethioate. The control S. cerevisiae treatment wine contained most ethyl 4-hydroxybutyrate and amyl methacrylate. The approach reported may have practical application in better understanding and managing the content and composition of odoriferous volatile esters in Malvazija istarska and wine in general. This study was funded by Croatian Science Foundation under the projects IP- 2020-02-4551 and DOK-2021-02-5500.