Effects of vine or bunch shading on the glycosylated flavor precursors in grapes of Vitis vinifera L. Cv. syrah.

Effects of the modification of vine or bunch environment on glycoconjugates were studied in Syrah berries over two years. Vines were shaded from berry set to maturity, with black polyethylene nets of different mesh size to obtain 30 and 50% of the direct sunlight. Bunches were naturally shaded by the leaves or artificially with 90% shade bags. Sun-exposed berries were chosen as control berries. A quantitative decrease in levels of glycoconjugates was observed in shaded bunches, particularly for phenolic and C(13)-norisoprenoidic glycosides. In the same way, vine shading caused a decrease in the contents of glycosides of terpenols, phenols, and C(13)-norisoprenoids in berries, but the grape environment (microclimate) affected the berry composition more than the vine environment. A cluster thinning experiment confirmed the independence of grapes with regard to the plant for the biosynthesis of the C(13)-norisoprenoid glycosides.

Quantitative determination of free and hydrolytically liberated beta-damascenone in red grapes and wines using a stable isotope dilution assay.

Quantitative analysis of free and hydrolytically liberated beta-damascenone in grapes and wines was developed, using a stable isotope dilution assay. Free beta-damascenone was isolated from grapes and wines by diethyl ether-hexane (1:1, v/v) extraction and the precursor(s) (glycosidic, polyols) of beta-damascenone using Sep-Pak Plus C18 RP cartridges. Hydrolytically liberated beta-damascenone was generated by acid hydrolysis from the precursor(s) extract. Red wines from Bordeaux (Merlot, Cabernet Sauvignon and Cabernet Franc, 1995 and 1996 vintage), Burgundy (Pinot Noir, 1995 and 1996 vintage) regions and Grenache wines from Chateauneuf du Pape and Côtes du Rhône (1995 vintage) were analysed to quantify free beta-damascenone. The wines made from Grenache and Cabernet Sauvignon (1996 vintage) grapes presented the highest mean amounts of free beta-damascenone, 5.4 and 5.5 micrograms l-1, respectively. Merlot, Cabernet Sauvignon and Cabernet Franc grapes of Bordeaux (1996 vintage) and their corresponding wines were analysed for quantification of free and hydrolytically liberated beta-damascenone. The levels of hydrolytically liberated beta-damascenone in grapes could predict closely the levels of free beta-damascenone in the corresponding wines after one year of ageing, i.e., almost half the levels found for the grape samples. The influence of enzyme and heat treatment of Merlot wine samples on their beta-damascenone levels was studied. Heat treatment doubled the levels of this compound, but enzyme treatment generated, in the corresponding wines, half the levels of beta-damascenone found in the non-enzyme treated wines.

Quantitative determination of beta-ionone in red wines and grapes of Bordeaux using a stable isotope dilution assay.

Quantitative analysis of beta-ionone has been developed, using a stable isotope dilution assay. This was applied to red wines from different cultivars and regions. The Burgundy Pinot noir wines exhibited the highest levels of beta-ionone. The variation in the levels of beta-ionone in grape samples and in their corresponding wines, of Merlot, Cabernet Sauvignon and Cabernet franc from Bordeaux regions was monitored at four different stages towards the end of maturation: the levels of beta-ionone were almost similar, exhibiting only a slight decrease during maturation. beta-Ionone occurred in all the grapes and wines samples analysed at levels higher than, or close to its odour threshold which was determined in a model wine solution and was found to be of 90 ng l-1. In a previously supplemented model wine solution with beta-ionone (250 ng l-1), the odour threshold was found to be of 980 ng l-1 (total levels).

Quantitative determination of 2-methoxy-3-isobutylpyrazine in red wines and grapes of Bordeaux using a stable isotope dilution assay.

Quantitative analysis of 2-methoxy-3-isobutylpyrazine (MIBP) in grapes and wines was developed, using a stable isotope dilution assay. This was applied to red grapes and wines from the Bordeaux region. The grapes and the wines of the 1995 and 1996 vintages came from the three most frequently used varieties of the region, Merlot, Cabernet Franc and Cabernet Sauvignon. The wines made from Cabernet Sauvignon grapes exhibited levels of MIBP (mean concentration, 12 ng l-1 for 1996 vintage and 13 ng l-1 for 1995 vintage) close to or higher than its odour threshold in wines (10 ng l-1) and slightly higher than the amounts found in the Merlot wines (mean concentration, 8 ng l-1 for 1996 vintage and 4 ng l-1 for 1995 vintage), especially those of the 1996 vintage. The variation in the levels of MIBP in grape samples and in their corresponding wines was monitored at four different stages towards the end of maturation. MIBP was present in all grapes and wines analysed, even in surmaturation. A linear trend was observed between grapes and wines of the three cultivars during maturation.

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.