David Chassagne

The chemodiversity of wines can reveal a metabologeography expression of cooperage oak wood

Wine chemical compositions, which result from a complex interplay between environmental factors, genetic factors, and viticultural practices, have mostly been studied using targeted analyses of selected families of metabolites. Detailed studies have particularly concerned volatile and polyphenolic compounds because of their acknowledged roles in the organoleptic and therapeutic properties. However, we show that an unprecedented chemical diversity of wine composition can be unraveled through a nontargeted approach by ultrahigh-resolution mass spectrometry, which provides an instantaneous image of complex interacting processes, not easily or possibly resolvable into their unambiguous individual contributions. In particular, the statistical analysis of a series of barrel-aged wines revealed that 10-year-old wines still express a metabologeographic signature of the forest location where oaks of the barrel in which they were aged have grown.

Adsorption equilibria of water vapor on cork.

We report here for the first time a complete thermodynamic study of water vapor adsorption on crude cork powder and plate. Adsorption-desorption isotherms were accurately measured by thermogravimetry at 283, 298, and 313 K in a large range of relative pressure. Adsorption enthalpies were determined by calorimetry as a function of loading. Adsorption-desorption isotherms exhibit a hysteresis due to the swelling of the material. The influence of the presence of lenticels on the adsorption properties of cork is found to be negligible. A detailed analysis and interpretation of adsorption data allow proposal of an adsorption mechanism in two steps. (i) First, water adsorbs on hydrophilic sites constituted by hydroxyl and methoxyl groups. (ii) Then water adsorption continues by clusters formation around the hydrophilic sites.

Effects of yeast cell-wall characteristics on 4-ethylphenol sorption capacity in model wine.

Saccharomyces cerevisiae is an efficient biosorbant, used in winemaking to reduce the concentration of undesirable molecules such as fatty acids. Volatile phenols such as 4-ethylphenol, which causes a horsy smell in wine, are particular targets of this type of curative process. This study demonstrates that the sorption capacity of 4-ethylphenol by yeasts is greatly influenced by strain nature, methods, and medium used for biomass production and drying after harvesting. S. cerevisiae mutant strains with deletion of genes encoding specific proteins involved in cell-wall structure and composition were studied, and a major role for mannoproteins in 4-ethylphenol sorption was identified. It was confirmed that 4-ethylphenol sorption occurs at the surface of the yeast wall and that not all mannoproteins are determinants of sorption: the sorption capacity of cells with deletion of the Gas1p-encoding gene was 75% lower than that of wild type. Physicochemical properties of yeast cell surface have been also studied.

6-O-α-L-arabinopyranosyl-β-D-glucopyranosides as aroma precursors from passion fruit

Abstract The 6-O-α- l - Arabinopyranosyl -β- d - glucopyranosides of linalool, benzyl alcohol and 3-methyl-but-2-en-1-ol were isolated from passion fruit ( Passiflora edulis ) by adsorption chromatography on XAD-2 resin, then further extracted on the same resin after partial enzymic hydrolysis and semi-preparative chromatography on RP-18 phase by HPLC. Their structures were identified by 1 H NMR spectroscopy and mass spectral analysis and by methylation analysis of the carbohydrate moieties.

Enzymatic hydrolysis of edible Passiflora fruit glycosides

The combined action of Hemicellulase REG 2 and sweet almond glucosidase containing β-d-glucopyranosidase, α-l-rhamnopyranosidase, α-l-arabinopyranosidase and α-l-arabinfuranosidase activities allowed release of most of the volatile compounds bound as aglycones in edible Passiflora fruits. Great variability between the four species studied, P. edulis, P. edulis f falvicarpa, P. ligularis, P. molissima, was noticed. 2,5-Dimethyl-4-hydroxy-3-(2H) furanone (furaneol) was identified for the first time in bound form in purple and yellow passion fruit. Only geraniol was identified as the aglycone in P. molissima. and no terpenol is present in the hydrolysate obtained from P. ligularis. Several terpene diols: 2,6-dimethyl-1,8-octanediol, (E)- and (Z)-2,6-dimethylocta-2,7-diene-1,6-diol, 2,6-dimethylocta-3,7-dien-2,6-diol and 2,6-dimethylocta-1,7-dien-3,6-diol have been identified in both purple and yellow passion fruit and small amounts of (Z)-2,6-dimethylocta-2,7-diene-1,6-diol are present in P. molissima. α-Ionol derivatives oxygenated in position 3 seem to be characteristic of purple passion fruit whereas β-ionol compounds oxygenated in position 3 are the major norisoprenoids identified as the aglycone in yellow passion fruit. The bound norisoprenoid content of P. ligularis and P. molissima is low. Important concentrations of bound aromatic alcohols are found in purple and yellow passion fruit whereas phenolics can be considered as characteristic of purple varieties. ©

A cyanogenic glycoside from Passiflora edulis fruits

Cyanogenic β-rutinoside ((R)-mandelonitrile α-L-rhamnopyranosyl-β-d-glucopyranoside) was isolated from fruits of Passiflora edulis. Its structure was elucidated mainly by enzymatic hydrolysis using a specific enzyme, GC-mass spectrometric analysis of trifluoroacetyl derivatives, and NMR spectroscopy.

Role of wood macromolecules on selective sorption of phenolic compounds by wood.

Wood is a complex structure of various macromolecules, mainly cellulose, hemicellulose, and lignin. Although the sorption process of some organic compounds by wood has been elucidated, the relative contribution of its different fractions in the sorption mechanism is not clearly determined. Certain works predict the amount of organic compounds sorbed on wood as a direct relationship to its lignin fraction. All wood macromolecules, however, seem to have the capacity to sorb organic compounds. Sorption of phenolic compounds on individual wood macromolecules has been studied and compared to that on wood. Wood-water partition coefficients ( K wood) for phenolic volatiles and their sorption rates in the presence of lignin display a linear relationship. Results show that cellulose and hemicellulose sorb all phenolic compounds without apparent distinction, whereas lignin is a selective sorbent of these compounds. Sorbant availability and sorbate chemical structure seem to be the key factors governing the sorption mechanism. Sorption kinetics study gives apparent diffusion coefficient values of aroma compounds, bringing new kinetic data for understanding the ternary system of wood, hydroalcoholic solution, and phenolic compounds.

Free and bound flavour components of amazonian fruits. 1: Bacuri

The free and bound flavour components of bacuri fruits were analysed by capillary GC and GC–MS following XAD-2 separation. Seventy-five components were identified in the free volatile fraction; the most abundant were terpene alcohols, among them, linalol and related compounds, linalol furanoxides and pyranoxides, hotrienol and several dimethyl-octadiendiols. Abundant amounts of 4-methoxy-2,5-dimethyl-3(2H)-furanone were also found. Seven glucosides and three rutinosides were identified by GC–MS of their TFA derivatives for EI–MS and NCI–MS, in agreement with quantitative data obtained for enzymatically released aglycones and saccharidic moieties structure; the most important glycosides were benzyl, 2-phenylethyl, (E)-linalol furanoxide and (S)-linalol glucosides and benzyl, 2-phenylethyl, and (S)-linalol rutinosides. Glycosides possessing ‘unusual’ saccharidic moieties remained unidentified. Copyright

Determination of trifluoroacetylated glycosides by gas chromatography coupled to methane negative chemical ionization mass spectrometry

Abstract Gas chromatography coupled to methane chemical ionization mass spectrometry was used for qualitative determination of trifluoroacetylated plant glycosides. The mass spectra obtained exhibited characteristic fragment ions of the sugar moiety and molecular or pseudo-molecular ions. The pattern of these chemical ionization spectra was influenced by source temperature. This method was applied to the structural determination of glycosides from purple passion fruit and muscat wine (Muscat of Frontignan) extracts obtained by adsorption on Amberlite XAD-2.

Interaction Mechanisms between guaiacols and lignin: the conjugated double bond makes the difference.

Lignin is considered to be responsible for a selective sorption of phenolic compounds on wood. In order to investigate the mechanisms involved, two similar guaiacol compounds--only differing by the nature of the para side chain--were adsorbed on oak wood extracted lignin. Vapor sorption-desorption isotherms indicated that about 3.5 wt % of 4-vinylguaiacol is adsorbed near saturation whereas it is only 0.8% for 4-ethylguaiacol. For both compounds, the isotherms displayed a hysteresis though significantly greater for 4-vinylguaiacol. Analyses of the hydroxyl stretching region of FTIR spectra of the lignin/4-ethylguaiacol and lignin/4-vinylguaiacol complexes indicated that physisorption via hydrogen bonds occurs for both sorbates with lignin phenolic hydroxyl groups but which would be more condensed for the former than for the latter. According to NMR spectra, these phenolic hydroxyl groups correspond to non-etherified guaiacyl subunits. In contrast with other para substituents, the conjugated vinyl bond favors not only physisorption but also chemisorption as witnessed by the fact that upon desorption in the vapor phase, even after pumping under dynamic vacuum for several days, about 1 wt % of 4-vinylguaiacol remains adsorbed onto lignin.