Abstract
Saccharomyces cerevisiae × Saccharomyces kudriavzevii hybrids are typically used for white wine fermentation because of their cryotolerance. One group of these hybrids presents a unique ability to release thiol varietal aroma products as well as excessive amounts of acetic acid under specific conditions, which is detrimental for wine organoleptic quality. The aim of this work is to better assess the effects of lipids, sugar concentrations and temperature on the production of acetic acid and thiols during wine fermentation. To this end, we used a Box–Behnken experimental design and response surface modeling on the production of acetic acid and thiols in S. cerevisiae × S. kudriavzevii hybrids from the Eg8 family during fermentation of a synthetic must. We showed that these hybrids produced lower levels of acetic acid when the initial lipid concentration was increased, whereas they produced greater levels when the initial sugar concentration was high. Moreover, we found that lipids had a positive impact on the final concentrations of 4-methyl-4-mercaptopentan-2-one and 3-mercaptohexan-1-ol (3MH), giving box tree and citrus flavors, respectively. The increase of 3MH was concomitant with a decrease of 3-mercaptohexyl acetate (3MHA) characterized by a passion fruit aroma, indicating that lipid addition reduces the rate of 3MH acetylation into 3MHA. These results highlight the key role of lipid management in acetic acid metabolism and thiol release by S. cerevisiae × S. kudriavzevii hybrids and underline its technological interest in alcoholic fermentation to avoid the overproduction of volatile acidity while favoring the release of volatile thiols.
Highlights
Saccharomyces cerevisiae wine strains form a cluster apart from S. cerevisiae strains from different origins, presenting genetic variations compared to S. cerevisiae from other ecological niches (Legras et al 2007, 2018; Liti et al 2009; Peter et al 2018)
Each varietal thiol brings a particular aroma to the wine: 4-methyl-4-mercaptopentan2-one (4MMP) is characteristic of box tree aroma, while 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) give fruity aromas, citrus and passion fruit flavors, respectively. 4MMP and 3MH are mainly liberated in the medium from odorless precursors present in the grape must (Cysteine-4MMP, Glutathione-4MMP, Cysteine-3MH, and Glutathione-3MH) owing to a yeast beta-lyase (Howell et al 2005; Thibon et al 2008; Holt et al 2011; Roncoroni et al 2011), and 3MH can be acetylated into 3MHA by Atf1p, an acetyltransferase produced by the yeast (Roland et al 2011)
Eg8 is a S. cerevisiae × S. kudriavzevii natural hybrid mainly used in white wine fermentation because of its cryophilic character and its strong ability to release varietal thiols
Summary
Saccharomyces cerevisiae wine strains form a cluster apart from S. cerevisiae strains from different origins, presenting genetic variations compared to S. cerevisiae from other ecological niches (Legras et al 2007, 2018; Liti et al 2009; Peter et al 2018). The Eg8 industrial strain, which belongs to this group, was originally isolated in 1979 from a vat fermenting at low temperature in Alsace (France) and was described as a triploid S. cerevisiae × S. kudriavzevii hybrid for the first time in 2012 (Erny et al 2012). This strain and its variants, further called the Eg8 family, are mainly used in white wine fermentations because of their cryophilic characteristics and because of their ability to release a high amount of varietal thiols under oenological conditions (Murat et al 2001). Each varietal thiol brings a particular aroma to the wine: 4-methyl-4-mercaptopentan2-one (4MMP) is characteristic of box tree aroma, while 3-mercaptohexan-1-ol (3MH) and 3-mercaptohexyl acetate (3MHA) give fruity aromas, citrus and passion fruit flavors, respectively. 4MMP and 3MH are mainly liberated in the medium from odorless precursors present in the grape must (Cysteine-4MMP, Glutathione-4MMP, Cysteine-3MH, and Glutathione-3MH) owing to a yeast beta-lyase (Howell et al 2005; Thibon et al 2008; Holt et al 2011; Roncoroni et al 2011), and 3MH can be acetylated into 3MHA by Atf1p, an acetyltransferase produced by the yeast (Roland et al 2011)
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