Development and validation of an LC-FTMS method for quantifying natural sweeteners in wine.

The quality of a wine largely depends on the balance between its sourness, bitterness and sweetness. Recently, epi-dihydrophaseic acid-3'-O-ß-glucopyranoside (epi-DPA-G) and astilbin, two molecules obtained from grapes, have been shown to contribute notably to the sweet taste of dry wines. To study the parameters likely to affect their concentration, a new method was developed and optimized by LC-FTMS. Three gradients and five C18 columns were tested. Good results in terms of linearity (r2 > 0.9980), repeatability (RSD ≤ 3%), recovery (≥89%) and LOQ (≤20 µg.L-1) were obtained. The method was used to screen epi-DPA-G and astilbin in red wines of several vintages over one century. Both compounds were detected in all wines at concentrations varying from 1.2 to 14.7 mg/L for epi-DPA-G and from 0.5 to 42.6 mg/L for astilbin. Therefore, this new method can be used to quantify epi-DPA-G and astilbin reliably in wine.

Triterpenoids from Quercus petraea: Identification in Wines and Spirits and Sensory Assessment.

Eight new triterpenoids (1-8), the known genin (9), and two known functionalized triterpenoids (10 and 11) were isolated from a Quercus petraea heartwood extract. The structures of the new compounds were unequivocally elucidated using HRESIMS and 1D/2D NMR experiments. Sensory analyses were performed in a non-oaked wine on the pure compounds 1-11. Except compounds 1 and 11, all molecules exhibited a sweet taste at 5 mg/L that was particularly intense for compounds 3 and 9. Using LC-HRMS, compounds 1-11 were observed in an oak wood extract and in oaked red wine and cognac. They were also semiquantified in several samples of sessile ( Q. petraea) and pedunculate ( Q. robur) oak wood extract. All compounds were found in quantities significantly higher in sessile than in pedunculate oak wood. These results support the hypothesis of their contribution to the increase in sweetness during oak aging and show that they can be used as chemical markers to identify the species of oak used for cooperage.

Taste-guided isolation of sweet-tasting compounds from grape seeds, structural elucidation and identification in wines.

This work aimed at improving knowledge about sweetness in dry wines. Following on from the empirical observations of winegrowers, we assessed the contribution of grape seeds to wine sensory properties. An inductive fractionation method guided by gustatometry was used to isolate and characterize sweet-tasting compounds from grapes. Fractionation of grape seed macerates was achieved by liquid-liquid extraction, centrifugal partition chromatography (CPC) and preparative HPLC. Then, the structures of the purified compounds were elucidated by use of FTMS and NMR. Five compounds were identified: two new compounds, 2-hydroxy-3-methylpentanoic-2-O-ß-glucopyranoside (H3MP-G) and 2-hydroxy-4-methylpentanoic-2-O-ß-glucopyranoside acids (H4MP-G), along with gallic-4-O-ß-glucopyranoside acid (AG-G), 3-indolyl-(2R)-O-ß-d-glycoside lactic acid (ILA-G) and epi-DPA-3'-O-ß-glucopyranoside acid (epi-DPA-G). These compounds exhibited various levels of sweetness in a hydro-ethanolic solution and in white and red wines. Additionally, H3MP-G, H4MP-G and epi-DPA-G were identified for the first time in grapes and wines, whereas AG-G has already been reported in white grapes but never in wine.

Development of a quantitation method to assay both lyoniresinol enantiomers in wines, spirits, and oak wood by liquid chromatography-high resolution mass spectrometry.

Wine taste balance evolves during oak aging by the release of volatile and non-volatile compounds from wood. Among them, an enantiomer of lyoniresinol, (+)-lyoniresinol, has been shown to exhibit bitterness. To evaluate the impact of (+)-lyoniresinol on wine taste, a two-step quantitation method was developed and validated. First, (±)-lyoniresinol was assayed in wines, spirits, and oak wood macerates by C-18 liquid chromatography-high resolution mass spectrometry (LC-HRMS). Then, the lyoniresinol enantiomeric ratio was determined by chiral LC-HRMS in order to calculate the (+)-lyoniresinol content. In red and white wines, the average concentrations of (+)-lyoniresinol were 1.9 and 0.8 mg/L, respectively. The enantiomer proportions were not affected by bottle aging, and lyoniresinol appeared to remain stable over time. The sensory study of (+)-lyoniresinol established its perception threshold at 0.46 mg/L in wine. All the commercial wines quantitated were above this perception threshold, demonstrating its impact on wine taste by an increase in bitterness. In spirits, (+)-lyoniresinol ranged from 2.0 to 10.0 mg/L and was found to be released continuously during oak aging. Finally, neither botanical origin nor toasting was found to significantly affect the (+)-lyoniresinol content of oak wood. Graphical abstract From oak wood to wine: evaluation of the influence of (+)-lyoniresinol on the bitterness of wines and spirits.

How stereochemistry influences the taste of wine: Isolation, characterization and sensory evaluation of lyoniresinol stereoisomers.

Wine expresses its beauty by sending a sensory message to the taster through molecules coming from grapes, yeast metabolism or oak wood. Among the compounds released during barrel aging, lyoniresinol has been recently reported as a relevant contributor to wine bitterness. As this lignan contains three stereogenic carbons, this work aimed at investigating the influence of stereochemistry on wine taste by combining analytical and sensorial techniques. First, an oak wood extract was screened by Liquid Chromatography-High Resolution Mass Spectrometry to target isomers separable in a symmetric environment and a diastereoisomer called epi-lyoniresinol was isolated for the first time. Then, an original racemic resolution based on natural xylose-derivatives was carried out to obtain lyoniresinol enantiomers. Chiroptical spectroscopic measurements associated with theoretical calculations allowed the unambiguous determination of their absolute configuration. The taste properties of all these stereoisomers revealed that only one lyoniresinol enantiomer is strongly bitter whereas the other one is tasteless and the diastereoisomer is slightly sweet. The presence of these three compounds was established in an oaked Bordeaux wine by chiral and non-chiral chromatography, suggesting the significant influence of stereochemistry on wine taste.