Nitrogen catabolite repression modulates the production of aromatic thiols characteristic of Sauvignon Blanc at the level of precursor transport

Abstract

The free thiols 3-mercapto-hexanol (3MH) and its acetate, practically absent from musts, are liberated by yeast during fermentation from a cysteinylated precursor [S-3-(hexan-1-ol)-l-cysteine (Cys-3MH)] present in the grape must and contribute favorably to the flavor of Sauvignon white wines. Production of 3MH is increased when urea is substituted for diammonium phosphate (DAP) as the sole nitrogen source on a synthetic medium. On grape must, complementation with DAP induces a decrease of 3MH production. This observation is reminiscent of nitrogen catabolite repression (NCR). The production of 3MH is significantly lower for a gap1Delta mutant compared with the wild type, during fermentation of a synthetic medium containing Cys-3MH as the precursor and urea as the sole nitrogen source. Mutants isolated from an enological strain with a relief of NCR on GAP1 produce significantly higher amounts of 3MH on synthetic medium than the parental strain. These phenotypes were not confirmed on grape must. It is concluded that on synthetic medium, Cys-3MH enters the cell through at least one identified transporter, GAP1p, whose activity is limiting the release of volatile thiols. On grape must, the uptake of the precursor through GAP1p is not confirmed, but the effect of addition of DAP, eventually prolonging NCR, is shown to decrease thiol production.

Unravelling glutathione conjugate catabolism in Saccharomyces cerevisiae: the role of glutathione/dipeptide transporters and vacuolar function in the release of volatile sulfur compounds 3-mercaptohexan-1-ol and 4-mercapto-4-methylpentan-2-one

“…γ-Glu-Cys-3-MH and Cys-3-MH were detected extracellularly in our ferments, suggesting these conjugates can be exported from the vacuole and then in turn from the cytosol. At least 50 % of Cys-3-MH enters the cell through GAP1 (Subileau et al 2008a), suggesting this type of cycling is possible, and our results show that the transporter PTR2 might be involved in cycling the dipeptide γ-Glu-Cys-3-MH in and out the cell. (6) Cleavage of Cys-X.…”

“…Recent evidence suggests that other metabolic pathways may also contribute to 3-MH formation during fermentation . Other genes involved in polyfunctional thiol release include GAP1 (Subileau et al 2008a), encoding the general amino acid permease, nine genes related to the sulphur amino acid pathway, and eight genes related to nitrogen catabolite repression or other amino acid pathways .…”

Sauvignon Blanc Wine: Contribution of Ageing and Oxygen on Aromatic and Non-aromatic Compounds and Sensory Composition : A Review

“…Practices such as mechanical harvesting, skin contact, pressure during pressing and oxygen exposure could significantly increase the precursor content in the juice and influence the volatile thiol concentration in the corresponding wines (Maggu et al, 2007;Patel et al, 2010;Roland et al, 2010b;Capone & Jeffery, 2011). The liberation of the volatile thiols from the respective precursors depends on conditions such as yeast strain, nitrogen availability and fermentation temperature (Murat et al, 2001a;Masneuf-Pomarède et al, 2006;Swiegers et al, 2006;Subileau et al, 2008b;Anfang et al, 2009;Harsch et al, 2013). More detail regarding the influence of these processes on the volatile thiol concentrations can be obtained from a review article published in 2012 (Coetzee & Du Toit, 2012).…”

Yeast selection for wine flavour modulation

“…The addition of urea in the medium decreases volatile thiols release indirectly, suggesting that the NCR control of precursor uptake. Moreover, the deletion of the general amino acid transporter GAP1 reduced 3SH release in a laboratory yeast background (Subileau et al, 2008b). Nevertheless, the deletion of URE2 did not modify precursor uptake from the must .…”

“…The figure shows the major mechanism of volatile thiols release during the alcoholic fermentation. Cysteinylated precursors R-Cys are taken up by yeast by amino acid transporters including Gap1p (Subileau et al, 2008b) and then cleaved into volatile thiols by the cystathionine β-lyase Irc7p and probably other unidentified β-lyases. Its related gene IRC7 is transcriptionally regulated by the Gln3p/Ure2 regulator pairs and is activated by the depletion of a nitrogen-rich source according to the NCR model .…”