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Roland A.,Interloire | Roland A.,Montpellier SupAgro | Vialaret J.,Ecole Polytechnique Federale de Lausanne | Moniatte M.,Ecole Polytechnique Federale de Lausanne | And 3 more authors.
Journal of Chromatography A | Year: 2010

A rapid nanoLC-MS/MS method was developed and validated for the simultaneous determination of glutathionylated and cysteinylated precursors of 3-mercapto-hexan-1-ol (3MH) and 4-methyl-4-mercaptopentan-2-one in grape juice using stable isotope dilution assay (SIDA). The analytes were extracted from must using a cation exchange resin and purified on C18 cartridges. They were chromatographically separated on a reverse phase column and finally analyzed by tandem mass spectrometry in selected reaction monitoring mode (SRM) using deuterated analogues as standards except for glutathionylated conjugate of 4MMP which was analyzed by external calibration. The method was validated according to the International Conference on Harmonization recommendations by determining linearity, accuracy, precision, recovery, matrix effect, repeatability, intermediate reproducibility, LODs and LOQs. Calibration for each precursor was determined by performing Lack-of-Fit test and the best fitting for 3MH precursors was a quadratic model whereas a linear model was better adapted for 4MMP precursors. All calibration curves showed quite satisfactory correlation coefficients (R2 > 0.995 for SIDA quantification and R2 > 0.985 for external calibration). Quantification by SIDA and external calibration allowed a high level of accuracy since the averaged value ranged from 80 to 108%. Quantification of aroma precursors was accurate and reproducible over five days since intermediate precision (same analyst, same sample and same apparatus), which was evaluated by the calculation of RSD was inferior to 16%. Limits of quantification for G3MH and G4MMP were closed to 0.50 and 0.07 nmol/L and as 4.75 and 1.90 nmol/L for Cys3MH and Cys4MMP respectively. This method was applied to the quantification of precursors into several types of grape juices: Melon B., Sauvignon, Riesling and Gewurztraminer. © 2010 Elsevier B.V. All rights reserved. Source

Roland A.,Interloire | Roland A.,French National Institute for Agricultural Research | Cavelier F.,French National Center for Scientific Research | Schneider R.,IFV
Flavour and Fragrance Journal | Year: 2012

During the past 20 years, interest in the involvement of varietal thiols in the aroma of young wines has grown considerably. Most data in the literature dealing with these thiols in wine has focused on 4-mercapto-4-methylpentan-2-one, 3-mercaptohexyl acetate and 3-mercaptohexan-1-ol and demonstrate the central role of the different branches of chemistry in understanding the biotechnological processes responsible for thiol release. This review describes and discusses the chemical strategies used to synthesize volatile thiols and their precursors as well as their final use in order to: (1) elucidate the structure of the precursors, their role and the mechanism of cleavage; (2) determine the sensory contribution of volatile thiols in wine; and (3) develop accurate quantification methods. © 2012 John Wiley & Sons, Ltd. Source

Roland A.,Interloire | Roland A.,Montpellier University | Schneider R.,French National Institute for Agricultural Research | Charrier F.,Institute Francais Of La Vigne Et Du Vin | And 3 more authors.
Food Chemistry | Year: 2011

In order to examine varietal thiol precursors in both the skin and the pulp of grapes, two grape varieties, Melon B. and Sauvignon Blanc, were considered. We found that cysteinylated and glutathionylated precursors of 3-mercapto-1-hexanol and 4-methyl-4-mercapto-2-pentanone were preferentially in skin. In the Sauvignon Blanc variety, precursors were detected both in the skin and the pulp, while in Melon B., only S-3-(1-hexanol)glutathione was detected in pulp, any other precursors being exclusively found in skin. During an industrial pressing cycle, extraction of thiol precursors was enhanced at the end of the cycle (highest pressures), thus producing more varietal thiols in the resulting wines. Cold prefermentation skin contact did not influence the concentration of the measured precursors in Sauvignon Blanc must. Nevertheless, the release of thiol in resulting wines increased significantly between 1 and 7. days of cold prefermentation skin contact. This increase could be due to the formation of other thiol precursors, such as S-3-(1-hexanal)glutathione or S-3-(1-hexanal)cysteine, during prefermentative operations. © 2010 Elsevier Ltd. Source

Roland A.,Interloire | Vialaret J.,Ecole Polytechnique Federale de Lausanne | Razungles A.,Montpellier University | Rigou P.,Montpellier University | Schneider R.,Institute Francais Of La Vigne Et Du Vin
Journal of Agricultural and Food Chemistry | Year: 2010

Thiol precursor content in Melon B. and Sauvignon blanc grape juices obtained under vacuum was determined by quantifying cysteinylated and glutathionylated conjugates of 3-mercaptohexan-1-ol (3MH) and 4-methyl-4-mercaptopentan-2-one (4MMP). This characterization allowed the study of thiol precursor evolution during ripening of Sauvignon blanc grapes in several viticultural situations together with grape reaction product (GRP) and the main substrate of polyphenoloxidase, that is, caftaric acid. Concentration of precursors greatly increased during ripening except for the cysteinylated conjugate of 4MMP. Precursor evolution was also monitored during the oxidation of grape juice. Addition of oxygen to a grape juice set off the enzymatic oxidation of hydroxycinnamic acids but did not negatively affect precursor concentrations. Part of the glutathionylated precursor of the 3MH was produced during prefermentative operations (up to 140% in Sauvignon blanc). Consequently, this precursor naturally occurring in grapes was also formed during prefermentative operations. The proportion of biogenetic and prefermentary formation of the glutathionylated precursor of 3MH was different under industrial conditions depending on the grape variety considered. Addition of glutathione and hexenal in grape juices of Melon B. and Sauvignon induced an increase of the production of 3MH and consequently of its acetate in the resulting wines. Residual glutathione in must has to be preserved to enhance the aromatic potential of grapes. © 2010 American Chemical Society. Source

Roland A.,Interloire | Roland A.,Montpellier SupAgro | Schneider R.,French National Institute for Agricultural Research | Guerneve C.L.,Montpellier SupAgro | And 2 more authors.
Food Chemistry | Year: 2010

The isotopically labelled S-3-(hexan-1-ol)-glutathione d2/d3 (G3MHd2/d3) was synthesized with a strategy based on acid-labile protecting groups. The natural analogue of this compound could be a precursor of 3-mercaptohexanol, a varietal thiol reminiscent of grape fruit, released during alcoholic fermentation. In a first time, deuterated glutathione conjugate was used to perform identification and quantification by stable isotope dilution assay of G3MH in musts from several varieties: Sauvignon, Riesling and Gewurztraminer. In a second time, synthetic and natural musts (Sauvignon Blanc) were spiked by G3MHd2/d3 at different levels from 12 to 150 μg L-1 to demonstrate the relationship between 3-mercaptohexan-1-ol (3MH) and G3MH. GC-ITMS/MS analysis of the resulting wines clearly showed the formation of the corresponding deuterated 3MH, that proves the direct connection with G3MH under enological conditions. In Sauvignon Blanc grape juice, a conversion yield of 4.4% was found in duplicate for an initial spiking of G3MH d2/d3 equivalent to 12 μg L-1. © 2010 Elsevier Ltd. All rights reserved. Source

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