New Insights on 3-Mercaptohexanol (3MH) Biogenesis in Sauvignon Blanc Wines: Cys-3MH and (E)-Hexen-2-al Are Not the Major Precursors

Abstract

The molar conversion yield of Cys-3MH into 3MH, during alcoholic fermentation, was traced using a deuterated isotope of the precursor added to different Sauvignon Blanc musts. This yield is close to that found in synthetic media supplemented with synthetic Cys-3MH, that is, below 1%. Yet, this represents only 3-7% of the total 3MH production in wine. This clearly shows that Cys-3MH is a precursor of 3MH, but not the main one in the different musts tested. The contribution of ( E)-hex-2-enal, which has been suggested as another potential precursor of 3MH, was discarded as well, as shown using also a deuterated analogue. The third suggested precursor of 3MH is a glutathionyl-3MH (G-3MH), which upon proteolytic degradation could release Cys-3MH. The knockout of the OPT1 gene, which encodes the major glutathione transporter, reduces 3MH accumulation by a 2-fold factor in grape must as compared to the wild type strain. Consequently, it is deduced that major 3MH precursor(s) are transported into yeast via Opt1p, which is in favor of G-3MH being a 3MH precursor. This work opens the search for the major natural precursor(s) of 3MH in Sauvignon Blanc must.

Origins of Grape and Wine Aroma. Part 1. Chemical Components and Viticultural Impacts

“…It has been shown more recently that glutathione precursors are an equally, if not more important, source of these pleasant smelling polyfunctional thiols (Subileau et al 2008, Fedrizzi et al 2009, Grant-Preece et al 2010, Roland et al 2010, Winter et al 2010. A recent study documented that the glutathione-conjugated 3MH diastereomers were up to 35 times more abundant than their cysteineconjugated counterparts in juices of Sauvignon blanc, Riesling, Chardonnay, and Pinot Grigio; Sauvignon blanc juices generally had the highest concentrations of the varieties studied .…”

“…A main research focus has been on the release of polyfunctional thiols during fermentation, due primarily to the fact that yeasts have limited and varied capacity to liberate the polyfunctional thiols from their precursors (Subileau et al 2008, Winter et al 2011. For example, estimates from the literature vary from 0.1 to 12% conversion of cysteine-3MH to 3MH (and 3MHA) (Subileau et al 2008), representing only a small fraction of the polyfunctional thiols present in juice and leaving significant pools of both cysteine and glutathione precursors in finished wines .…”

“…For example, estimates from the literature vary from 0.1 to 12% conversion of cysteine-3MH to 3MH (and 3MHA) (Subileau et al 2008), representing only a small fraction of the polyfunctional thiols present in juice and leaving significant pools of both cysteine and glutathione precursors in finished wines . It has been established that yeast strains having carbon-sulfur β-lyase activity release these polyfunctional thiols during fermentation (Howell et al 2005, Ugliano 2009, Holt et al 2011.…”

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

“…Some precursors in the juice have been identified as being cysteinylated or glutathionylated precursors (Tominaga et al, 1998b;Peyrot des Ganchos et al, 2002;Fedrizzi et al, 2009). However, studies have shown that these precursors account for only a fraction of the total amount of thiols present in the wine (Subileau et al, 2008a;Roland et al, 2010a;2010b), and no direct correlation between precursor concentration and the amount of free volatile thiols in the resulting wines has been observed Roland et al, 2011;Pinu et al, 2012). Other than release from precursors, the biogenesis of volatile thiols also has been proposed.…”

Occurrence and Analysis of Sulfur Compounds in Wine

“…However, several researches have indicated that no clear correlation between precursor concentrations in must and free thiol concentration in wine exist [8,16,59,73,80,[85][86][87][88][89].…”