Associations between the sensory attributes and volatile composition of Cabernet Sauvignon wines and the volatile composition of the grapes used for their production.

The sensory properties of wine are influenced by the chemical composition of the grapes used to produce them. Identification of grape and wine chemical markers associated with the attributes perceived by the consumer of the wine will enable better prediction of the potential of a parcel of grapes to produce wine of a certain flavor. This study explores the relationships between Cabernet Sauvignon grape volatile composition and wine volatile profiles with the sensory properties of wines. Twenty grape samples were obtained from nine vineyard sites across three vintages and wines vinified from these parcels using controlled winemaking methods. The volatile composition of the grapes were analyzed by SBSE-GCMS, the wines were analyzed by SPME-GCMS, and these data sets were compared to that obtained from the sensory analysis of the wines. Statistical treatment of the data to account for vintage and region effects allowed underlying relationships to be seen between wine sensory attributes and wine or grape volatile components. The observed associations between grape or wine volatile compounds and wine sensory attributes has revealed target compounds and pathways whose levels may reflect the biochemical effects on grape composition by differing growth conditions during berry development and ripening. The compounds identified in this study may be useful grape or wine markers for potential wine sensory characteristics.

Induction of secondary metabolism in grape cell cultures by jasmonates.

The use of a genetic approach to study the biosynthetic pathways leading to the production of secondary metabolites in grapes is difficult given the long generation times and difficulty in transforming this species. In the present study, GC/MS and microarray experiments were used to identify compounds produced in grape cell cultures in response to jasmonates and to examine the expression of genes from pathways that produce these secondary metabolites. Methyl jasmonate (MeJA) and jasmonic acid (JA) treatments resulted in the production of at least 25 compounds with sesquiterpene-like mass spectra in the cell cultures. A significantly greater amount of proanthocyanidins was produced in the MeJA-treated cell cultures compared with controls and stilbene biosynthesis was induced in both MeJA- and JA-treated cells. Salicylic acid (SA) suppressed the MeJA-associated increase in sesquiterpenes and proanthocyanidins, but SA did not suppress the stilbene production induced by MeJA treatment. The mechanism by which jasmonates induced secondary metabolite production in cultured grape cells varied depending on the pathway. The increased production of proanthocyanidins and stilbenes was associated with the induction of all of the genes in associated biosynthesis pathways, including those involved in the production of phenylalanine, whereas increased sesquiterpene synthesis was linked to the induction of certain genes from relevant biosynthesis pathways.

Generation of (E)-1-(2,3,6-trimethylphenyl)buta-1,3-diene from C13-norisoprenoid precursors.

Three C(13)-norisoprenoid compounds, 3,6,9-trihydroxymegastigma-4,7-diene (6), 3,4,9-trihydroxymegastigma-5,7-diene (4), and the actinidols (8), have all been synthesized and subjected to acid hydrolysis. All three were shown to generate (E)-1-(2,3,6-trimethylphenyl)buta-1,3-diene (1) under wine conservation conditions. At 45 degrees C, approximately 4000-5000 ng/L of 1 was formed from 1.0 mg/L of precursor, after 173 days, while at 25 degrees C more wine-like amounts (200-600 ng/L) were observed. A glucoside, 4,5-dihydrovomifoliol-C(9)-beta-d-glucopyranoside (9b), was isolated from grapevine leaves by multilayer coil countercurrent chromatography (MLCCC), and its stereochemistry was deduced as being (5R, 6S, 9R) by NMR and CD spectroscopy. Hydrolysis of this glucoside produced 1, but in quantities insufficient to account for the levels observed in wine.

Quantitative analysis, occurrence, and stability of (E)-1-(2,3,6-Trimethylphenyl)buta-1,3-diene in wine.

A stable isotope dilution assay has been developed for quantification of (E)-1-(2,3,6-trimethylphenyl)buta-1,3-diene (4) in wine using a [(2)H(6)]-analogue. Using this method, 4 was found in 96 out of 97 white wines, but in none of 12 red wines analyzed. 4 was found to be most prevalent in Semillon wines, followed by Chardonnay, with Riesling showing the least amount of 4 among these three varieties. 4, like 1,1,6-trimethyldihydronaphthalene (TDN, 3), appears to be formed during the aging process. 4 was found to be unstable in model wine, and in both white and red wine, with the order of stability being model > white > red. In a PVPP-stripped red wine, the rate of degradation of 4 was substantially lessened, with the final concentrations very close to those observed in model wine. When treated with either grape or wine tannin extracts in model wine, the concentration of 4 was found to decrease to levels very close to those observed with an untreated red wine. When white wine was heated at 45 degrees C, 4 was formed, indicating the presence of precursor forms. The amounts formed were much higher than those found in a commercial white wine. 4 was also observed in red wine heated to 45 degrees C, but the concentration produced was much less than that with white wine.