Influence of wine structurally different polysaccharides on the volatility of aroma substances in a model system.

The influence of native polysaccharides on wine organoleptic quality has not been yet clarified. Hence, the effect of purified fractions of arabinogalactan-proteins (AGPs), monomeric and dimeric rhamnogalacturonans II (mRG-II and dRG-II), and mannoproteins (MPs) on the volatility of various aroma substances was examined using the exponential dilution technique. The volatility of isoamyl acetate and ethyl hexanoate in a model wine system was not affected upon addition of wine polysaccharides in the range 5-20 g/L. At higher levels, the two esters were significantly retained in solution in the presence of the protein-rich polysaccharides MP0 and AGP0 and weakly salted out in the presence of the uronic acid-rich fractions AGP4, mRG-II, and dRG-II. In addition, the volatility increase caused by dRG-II on the esters was reversed when water was used as the solvent. 1-Hexanol exhibited retention in water with four fractions in the strength order AGP0 > dRG-II > mRG-II > AGP4 but was strongly salted out in the presence of fraction MP0. Furthermore, the diacetyl activity in water was overall not modified increasing only at high concentrations of AGP4. Reference polysaccharides dextrin and dextran were used for binding strength comparison.

Interactions between wine polyphenols and aroma substances. An insight at the molecular level.

Control of the organoleptic quality of wine or grape-derived beverages requires the study of the interactions between flavor volatiles and polyphenols. The influence of catechin and a wine highly condensed tannin fraction on the volatility of aroma substances was investigated using a dynamic headspace technique. In a hydroalcoholic solution, isoamyl acetate, ethyl hexanoate, and benzaldehyde appeared to be more retained than limonene at low catechin concentrations (0-5 g/L). The tannin fraction induced a slight decrease of benzaldehyde volatility and a salting out of limonene and had no effect on the two esters. Furthermore, investigations at the molecular level were conducted using (1)H NMR spectroscopy. Chemical shift changes registered upon addition of a ligand to a substrate kept at constant concentration allowed the determination of the dissociation constant in a 1:1 binding model. Complexation with catechin was evaluated to be similarly weak for benzaldehyde and the two esters. In addition, catechin and epicatechin displayed a higher affinity for benzaldehyde than for 3, 5-dimethoxyphenol, supporting the hypothesis of a hydrophobic driving force.

6-O-alpha-L-Arabinopyranosyl-beta-D-glucopyranosides as aroma precursors from passion fruit.

The 6-O-alpha-L-Arabinopyranosyl-beta-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 1H NMR spectroscopy and mass spectral analysis and by methylation analysis of the carbohydrate moieties.

Analytical methods for monoterpene glycosides in grape and wine. II. Qualitative and quantitative determination of monoterpene glycosides in grape.

Free and glycosidically bound terpenes of five Vitis vinifera grape cultivars (muscat of Alexandria, muscat of Frontignan, muscat of Hamburg, muscat Ottonel and Gewürztraminer) were investigated. The free and bound fractions were separated by selective retention on Amberlite XAD-2 resin. The glycosidic fractions were analysed by gas chromatography and gas chromatography-mass spectrometry using either enzymic hydrolysis and subsequent analysis of the released aglycones or trimethylsilyl (TMS) and trifluoroacetyl derivatives. The known monoterpenyl, benzyl and 2-phenylethyl beta-D-glucopyranosides, beta-rutinosides, 6-O-alpha-L-arabinofuranosyl-beta-D-glucopyranosides and 6-O-beta-D-apiofuranosyl-beta-D-glucopyranosides were determined. A number of other glycosides were detected and the structures of some of them, mainly apiosylglucosides and glucosides with aglycones in higher oxidation state than linalol, were tentatively identified using the mass spectra of their TMS and TFA derivatives and the results obtained from the analysis of their aglycones.

Analytical methods for monoterpene glycosides in grape and wine. I. XAD-2 extraction and gas chromatographic-mass spectrometric determination of synthetic glycosides.

Synthetic monoterpene and aromatic beta-D-glucopyranosides, beta-rutinosides and 6-O-(alpha-L-arabinofuranosyl)-beta-D-glucopyranosides and their corresponding alcohols, diluted in a synthetic solution imitating wine, were isolated and separated by selective retention on Amberlite XAD-2. The corresponding recoveries and the conditions for the direct determination of these glycosides by gas chromatography and gas chromatography-mass spectrometry after derivatization were determined. Trifluoroacetylation gave the best results but trimethylsilylation provided complementary results. The separation of some diastereoisomeric monoterpene glycosides was also examined.