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.     

Contribution of benzenemethanethiol to smoky aroma of certain Vitis vinifera L. wines

Benzenemethanethiol, a volatile thiol with a strong empyreumatic aroma reminiscent of smoke, has been identified in boxwood (Buxus sempervirens L.) as well as in red and white Vitis vinifera L. wines. The perception threshold in a model hydroalcoholic solution is approximately 0.3 ng/L. All of the wines analyzed for this study contained this compound in concentrations of several dozen nanograms per liter. The Chardonnay wines had 30-40 ng/L. Sensory discrimination between a wine containing 7 ng/L benzenemethanethiol and the same wine with an additional 4 ng/L is very significant; the difference in smell is described as "empyreumatic". This compound can therefore significantly contribute to the aroma of certain wines (Sauvignon Blanc, Semillon, Chardonnay, etc.) containing concentrations as high as 30-100 times higher than their perception threshold.     

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.     

From wine to pepper: rotundone, an obscure sesquiterpene, is a potent spicy aroma compound

An obscure sesquiterpene, rotundone, has been identified as a hitherto unrecognized important aroma impact compound with a strong spicy, peppercorn aroma. Excellent correlations were observed between the concentration of rotundone and the mean 'black pepper' aroma intensity rated by sensory panels for both grape and wine samples, indicating that rotundone is a major contributor to peppery characters in Shiraz grapes and wine (and to a lesser extent in wine of other varieties). Approximately 80% of a sensory panel were very sensitive to the aroma of rotundone (aroma detection threshold levels of 16 ng/L in red wine and 8 ng/L in water). Above these concentrations, these panelists described the spiked samples as more 'peppery' and 'spicy'. However, approximately 20% of panelists could not detect this compound at the highest concentration tested (4000 ng/L), even in water. Thus, the sensory experiences of two consumers enjoying the same glass of Shiraz wine might be very different. Rotundone was found in much higher amounts in other common herbs and spices, especially black and white peppercorns, where it was present at approximately 10000 times the level found in very 'peppery' wine. Rotundone is the first compound found in black or white peppercorns that has a distinctive peppery aroma. Rotundone has an odor activity value in pepper on the order of 50000-250000 and is, on this criterion, by far the most powerful aroma compound yet found in that most important spice.     

Determination of 2,4,6-trichloroanisole and 2,4,6-tribromoanisole in wine using microextraction in packed syringe and gas chromatography-mass spectrometry

A selective and fast method for the quantitative determination of 2,4,6-trichloroanisole (TCA) and 2,4,6-tribromoanisole (TBA) in wine was developed. Microextraction in packed syringe (MEPS) was optimized for the extraction and preconcentration of the analytes using extremely small volume samples (0.1-1 mL). For GC-EI-MS, the limit of detection (LOD) for red and white wine was in the range 0.17-0.49 microg L(-1) for TCA and TBA. In addition to GC-EI-MS both GC-NCI-MS and GC-HRMS were used to further improve both selectivity and sensitivity. The lowest LODs were achieved using GC-HRMS in the EI mode. In red and white wine samples the LODs were between 0.22-0.75 ng L(-1) for TCA and TBA. The reproducibility and linearity for the GC-HRMS method was good, with RSD-values of 4-10% for spiked red wine samples at 1 ng L(-1) and linearity with R (2) > 0.962 over a concentration range of 1 to 100 ng L(-1).     

Isolation and identification of 2-methoxy-3,5-dimethylpyrazine, a potent musty compound from wine corks

The compound responsible for a "fungal must" taint evident in industry assessments of wine corks was identified as 2-methoxy-3,5-dimethylpyrazine. The identification was made on the basis of gas chromatography/odor analyses, collection of material using micropreparative techniques, determination of chemical properties of collected material, and comparison by gas chromatography/mass spectrometry with an authentic sample, synthesized from 2-hydroxy-3,5-dimethylpyrazine. 2-Methoxy-3,5-dimethylpyrazine is an extremely potent compound with an unpleasant, musty, moldy aroma and an aroma threshold in a white wine of 2.1 ng/L. While its contribution to the frequency and intensity of cork taint in bottled wine is yet to be established, it has been assessed by some wine industry personnel as second only to 2,4,6-trichloroanisole as a cause of cork taint in Australian wine.     

Determination of free proline and monosaccharides in wine samples by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD)

A sensitive and selective analytical method for the simultaneous separation and quantitative determination of proline and free monosaccharides in wine samples by high-performance anion-exchange chromatography coupled with pulsed amperometric detection is described. Under optimized experimental conditions, a complete separation was obtained in less than 30 min, using an isocratic elution with 10 mM NaOH and 1 mM Ba(OAc)(2). No postcolumn addition of strong bases to the eluent for enhancing detection sensitivity was needed. Upon 25-fold sample dilution and purification to avoid interference of tannins, pigments, and phenolic compounds, the fingerprinting of common monosaccharides (i.e., arabinose, glucose, fructose, galactose, and xylose) and proline in wines, musts, and vinegars can be easily accomplished. The method allows high recovery and satisfies the necessary requirements for accuracy, repeatability, and sensitivity. Values obtained for proline content ranged from 470 to 1190 mg/L in "Aglianico" red wines (mean value, 870 +/- 192 mg/L, n = 21) and from 168 to 286 mg/L in white wines (mean value, 208 +/- 32 mg/L, n = 11). Lower levels were found in musts of red and white grapes, 550 and 87 mg/L, respectively. The lowest content of proline, ca. 10 mg/L, was found both in white and red vinegars.     

Isomeric influence on the oxidative coloration of phenolic compounds in a model white wine: comparison of (+)-catechin and (-)-epicatechin

The reactions of (+)-catechin and (-)-epicatechin with glyoxylic acid were studied in a model white wine solution. When the reactions were performed in darkness at 45 degrees C, the (-)-epicatechin concentration decreased more rapidly than that of (+)-catechin, and the (-)-epicatechin sample had twice the 440 nm absorbance of the (+)-catechin sample after the 14 day incubation period. The main pigments generated were identified as xanthylium cation pigments regardless of the isomeric character of the phenolic compound. Using a combination of absorbance and ion current data, the xanthylium cation pigments generated from (-)-epicatechin were found to have combined molar absorptivity coefficients 1.8 times that of the xanthylium cation pigments generated from (+)-catechin. The implication of these results on the development of an index of white wine oxidation susceptibility is discussed.     

Antioxidant capacities and phenolics levels of French wines from different varieties and vintages.

Phenolics from grapes and wines can play a role against oxidation and development of atherosclerosis. Levels of phenolics, major catechins [(+)-catechin, (-)-epicatechin, procyanidin dimers B1, B2, B3, and B4], phenolic acids (gallic acid and caffeic acid), caftaric acid, malvidin-3-glucoside, peonidin-3-glucoside, and cyanidin-3-glucoside were quantified by HPLC with UV detection for 54 French varietal commercial wines taken from southern France to study the antioxidant capacity and the daily dietary intake of these compounds for the French population. The highest antioxidant capacity was obtained with red wines and ranged from 12.8 mmol/L (Grenache) to 25.2 mmol/L (Pinot Noir). For white wines, Chardonnay enriched in phenolics by special wine-making was found to have an antioxidant capacity of 13.8 mmol/L, comparable to red wine values. For red wines classified by vintages (1996-1999) antioxidant capacities were approximately 20 mmol/L and then decreased to 13.4 mmol/L for vintages 1995-1991. Sweet white wines have 1.7 times more antioxidant capacity (3.2 mmol/L) than dry white wines (1.91 mmol/L). On the basis of a still significant French wine consumption of 180 mL/day/person, the current daily intake of catechins (monomers and dimers B1, B2, B3, and B4) averaged 5 (dry white wine), 4.36 (sweet white wines), 7.70 (rosé wines), 31.98 (red wines), and 66.94 (dry white wine enriched in phenolic) mg/day/resident for the French population. Red wine, and particularly Pinot Noir, Egiodola, Syrah, Cabernet Sauvignon, and Merlot varieties, or Chardonnay enriched in phenolics during wine-making for white varieties contribute to a very significant catechin dietary intake.     

Sulfate--a candidate for the missing essential factor that is required for the formation of protein haze in white wine

Protein haze formation in white wine is dependent on the presence of both wine protein and other unknown wine components, termed factor(s) X. The ability to reconstitute protein haze upon heating artificial model wine solutions (500 mg/L thaumatin, 12% ethanol, 4 g/L tartaric acid) to which candidate components were added was employed to identify factor(s) X. No protein haze was formed in the absence of additives. The individual or combined addition of caffeic acid, caftaric acid, epicatechin, epigallocatechin-O-gallate, gallic acid, or ferulic acid at typical white wine concentrations did not generate protein haze. However, PVPP fining of commercial wines resulted in a reduction in protein haze, suggesting that phenolic compounds may play a modulating role in haze formation. To elucidate the nature of the unknown factor(s) wine was fractionated and fractions were back-added to model wine and tested for their essentiality. Wine fractions were generated by ultrafiltration, reverse-phase chromatography, and mixed-mode anion-exchange and reverse-phase chromatography. The only purified fraction containing the essential component(s) was free of phenolic compounds, and analysis by mass spectrometry identified sulfate anion as the dominant component. Reconstitution with KHSO4 using either commercially available thaumatin or wine proteins confirmed the role of sulfate in wine protein haze formation. The two main wine proteins, thaumatin-like protein and chitinase, differed in their haze response in model wines containing sulfate. Other common wine anions, acetate, chloride, citrate, phosphate, and tartrate, and wine cations, Fe(2+/3+) and Cu(+/2+), when added at typical white wine concentrations were not found to be essential for protein haze formation.     

Method for the gas chromatographic assay with mass selective detection of trichloro compounds in corks and wines applied to elucidate the potential cause of cork taint

To investigate the role of trichloro compounds as a potential cause of "cork taint" in wine, an assay for trichloroanisole (TCA) and trichlorophenol (TCP) in corks and wine was developed utilizing solid phase extraction on a C(18) cartridge followed by gas chromatography with mass selective detection. Recovery and imprecision for TCA were 86-102 and 1.6-5.8%, respectively, and for TCP 82-103% and 1.7-3.9%, respectively. Limits of detection and quantitation were 0.1 and 2 ng/L, respectively, for TCA, and 0.7 and 4 ng/L, respectively for TCP. A survey of 2400 commercial wines revealed a higher incidence of cork taint in white wine than in red and in wines utilizing composite cork closures; wines from central Europe and Spain had higher overall rates of contamination and those from Canada and Italy the lowest. Significant but modest associations were found between the TCA and TCP contents of the wines and corks, but many wines exhibiting cork taint had low or undetectable concentrations of TCA. Over a 12-month period, experimentally bottled wines exhibited a slow increase in TCA and TCP content while cork closures manifested a decrease; most bottles showing cork taint contained low levels of TCA, and TCP concentrations were well below the sensory threshold. Neither compound was cytotoxic to human cell lines in culture up to final concentrations of 500 ng/mL. It was concluded that these two trichloro compounds are, at most, minor components of cork taint in commercial wines.     

Anthocyanin and proanthocyanidin content in selected white and red wines. Oxygen radical absorbance capacity comparison with nontraditional wines obtained from highbush blueberry

Antioxidant capacity, as measured by oxygen radical absorbance capacity (ORAC(PE)), total phenolic, total and individual anthocyanins, and proanthocyanidin fraction contents were evaluated in red and white wines from grapes. A comparison in terms of antioxidant capacity is made with nontraditional wines made from highbush blueberry. Blueberries are among fruits that are best recognized for their potential health benefits. In red wines, total oligomeric proanthocyanidin content, including catechins, was substantially higher (177.18 +/- 96.06 mg/L) than that in white wines (8.75 +/- 4.53 mg/L). A relative high correlation in red wines was found between ORAC(PE) values and malvidin compounds (r = 0.75, P < 0.10), and proanthocyanidins (r = 0.87, P < 0.05). In white wines, a significant correlation was found between the trimeric proanthocyanidin fraction and peroxyl radical scavenging values (r = 0.86, P < 0.10). A moderate drink (1 drink per day, about 140 mL) of red wine, or white wine, or wine made from highbush blueberry corresponds to an intake of 2.04 +/- 0.81 mmol of TE, 0.47 +/- 0.15 mmol of TE, and 2.42 +/- 0.88 mmol of TE of ORAC(PE)/day, respectively.     

White wine with red wine-like properties: increased extraction of grape skin polyphenols improves the antioxidant capacity of the derived white wine.

Lower antioxidant activity in white wines in comparison to red wines lies in the low grape-skin-derived polyphenol content. This paper reports the analysis of the antioxidant capacities of white wine samples obtained along two different processing procedures directed to enrich the wine with polyphenols. White wine samples derived from whole squeezed grapes stored for increasing periods of time (up to 18 h) contained increasing concentrations of polyphenols (from 0.35 to 0.55 mmol/L) and, in parallel, exhibited increased capacity to scavenge free radicals and to inhibit copper ion-induced low-density lipoprotein (LDL) oxidation. However, addition of increasing concentrations of alcohol (up to 18%) to the whole squeezed grapes remarkably augmented the extraction of grape skin polyphenols into the wine up to 1.25 mmol/L, resulting in an increased capacity of the wine to scavenge free radicals and to inhibit LDL oxidation, to an extent similar to that of red wine. The extent of LDL oxidation inhibition was directly related to the wine polyphenolic content (r = 0.986). It is concluded that processing white wine by imposing a short period of grape skin contact in the presence of alcohol leads to extraction of grape skin polyphenols and produces polyphenol-rich white wine with antioxidant characteristics similar to those of red wine.     

Sensory threshold of 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) and concentrations in young Riesling and non-Riesling wines

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) is well-known to contribute "petrol" aromas to aged Riesling wines, but its prevalence and contribution to young Riesling or non-Riesling wines is not well understood. TDN concentrations were measured in 1-3-year-old varietal wines produced from Cabernet franc (n = 14 wines), Chardonnay (17), Cabernet Sauvignon (4), Gewurztraminer (4), Merlot (9), Pinot gris (6), Pinot noir (9), Riesling (28), or Sauvignon blanc (6). TDN concentrations in the Riesling wines, 6.4 ± 3.8 μg/L, were significantly higher than in all other varietals, 1.3 ± 0.8 μg/L. The odor detection thresholds for TDN were then determined in both model wine and a neutral white wine. Group sensory thresholds were found to be the same in both matrices, 2 μg/L, indicating little masking of TDN due to the odorants in the neutral white. The TDN sensory threshold was a factor of 10 below the previously reported odor threshold. On the basis of this revised threshold, 27 of 28 Riesling wines had suprathreshold TDN, whereas only 7 of 69 non-Riesling wines had suprathreshold TDN. The monoterpenes linalool and geraniol were also measured in the Riesling wines, and odor activity values (OAVs) were calculated for the monoterpenes and TDN. The OAV for TDN was higher than for the monoterpenes in 25 of 28 Riesling wines.     

L-(-)-malic acid production by Saccharomyces spp. during the alcoholic fermentation of wine (1)

In an attempt to increase the acidity of wine by biological means, malate-producing yeasts were selected from a collection of 282 strains isolated in different parts of Spain. Only 4% of these strains (all of which belonged to Saccharomyces cerevisiae) produced l-(-)-malic acid in the range of 0.5-1 g/L. This was formed between days 2 and 6 of alcoholic fermentation, reaching a maximum on days 3 and 4; the concentration remained stable from day 7. Malic acid production was favored by temperatures in the 18-25 degrees C range and by musts with a high pH and low concentrations of sugar, initial malic acid, and yeast-assimilable nitrogen. Oxaloacetic acid, a precursor of malic acid, had no influence on malate production. The precursors pyruvic and fumaric acid did, however, have a significant effect on the production of this acid in some strains. No direct relation between pyruvate and malate metabolism was observed.     

Application of a headspace sorptive extraction method for the analysis of volatile components in South African wines

A headspace sorptive extraction (HSSE) in combination with thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) method for the analysis of volatile components (alcohols, esters, carbonyls, acids, phenols and lactones) in wine samples was developed. Extraction conditions such as salting-out effects, sorption time, stirring speed, phase ratio, extraction temperature, and effect of pH were thoroughly evaluated as part of method validation. The method was very sensitive with LODs and LOQs between 50 pg/L to 299 microg/L and 0.2 ng/L to 0.996 microg/L, respectively. Repeatability for all the compounds was between 3 and 22%. The intermediate repeatability was obtained within the acceptable range. Out of 39 volatile compounds selected, 37 were detected and quantitated. The method was found to be simple, cost-effective, sensitive, and use a small sample volume. The method was successfully applied for the routine analysis of 79 young red and white wine samples from various South African districts.     

Evolution and occurrence of 1,8-cineole (eucalyptol) in Australian wine

A new method has been developed for the quantitation of 1,8-cineole in red and white wines using headspace solid-phase microextraction (SPME) combined with stable isotope dilution analysis (SIDA) and gas chromatography-mass spectrometry (GC-MS). An extensive survey of Australian wines (44 white and 146 red) highlighted that only red wines contained significant amounts of 1,8-cineole (up to 20 μg/L). Hydrolytic studies with limonene and α-terpineol, putative precursors to 1,8-cineole, showed a very low conversion into 1,8-cineole (< 0.6%) over a 2 year period, which does not account for the difference between white and red wines. 1,8-Cineole was chemically stable in model wine solution over 2 years, and absorption from a Shiraz wine by bottle closures was most evident for a synthetic closure only (14% absorption after 1 year). Two commercial ferments at two different locations were monitored daily to investigate the evolution of 1,8-cineole throughout fermentation. Both ferments showed daily increases in 1,8-cineole concentration while in contact with grape solids, but this accumulation ceased immediately after pressing. This observation is consistent with the extraction of 1,8-cineole into the ferment from the solid portions of the grape berries.     

Iron(III) tartrate as a potential precursor of light-induced oxidative degradation of white wine: studies in a model wine system

The potential for iron(III) tartrate to act as a photoactivator in light-induced oxidative degradation of white wine is described. Using a tartaric-acid-based model wine system containing 5 mg/L iron, exposure to light from a xenon arc lamp led to the oxidative degradation of tartaric acid and the production of glyoxylic acid. The critical wavelength of light for the degradation process was found to be below 520 nm. No glyoxylic acid was formed in the absence of iron and/or light. Flint glass offered little protection from the light-induced photodegradation of tartaric acid. Antique Green glass offered more protection but did not stop the photodegradation process.     

Using LC-MSMS to assess glutathione levels in South African white grape juices and wines made with different levels of oxygen

The effect of oxygen on the levels of glutathione, an important antioxidant, in must and wine was studied using a novel LC-MSMS method for the analysis of reduced and oxidized glutathione. This study found that the storage of grape juice at high SO2 and ascorbic acid levels at -20 degrees C did not lead to a decrease in reduced glutathione levels. The effect of varying the oxygen levels in South African white grape juices, which included a reductive treatment (less than 0.3 mg/L dissolved O2 added), a control treatment (between 1.0 and 1.5 mg/L dissolved O2 added), and an oxidative treatment (3.5-4 mg/ L dissolved O2 added, without SO2) on reduced glutathione levels in the juice and resulting wine was also investigated. A custom build press was used to press whole bunches of two different Sauvignon Blanc and Colombard grapes. Alcoholic fermentation and oxygen additions to the must led to lower reduced glutathione levels in the wine. Reduced glutathione levels were only significantly higher in the wine made from reductive juice that had the highest initial reduced glutathione levels in the grapes.     

Determination of 24 pesticide residues in fortified wines by solid-phase microextraction and gas chromatography-tandem mass spectrometry

The present work describes a solid-phase microextraction (SPME) gas chromatography-tandem mass spectrometry (MS/MS) method to quantify 24 pesticides in fortified white wine and fortified red wine. In this study "fortified wine" refers to a wine in which fermentation is arrested before completion by alcohol distillate addition, allowing sugar and alcoholic contents to be higher (around 80-100 g/L total sugars and 19-22% alcohol strength (v/v)). The analytical method showed good linearity, presenting correlation coefficients (R(2)) ≥ 0.989 for all compounds. Limits of detection (LOD) and quantitation (LOQ) in the ranges of 0.05-72.35 and 0.16-219.23 μg/L, respectively, were obtained. LOQs are below the maximum residue levels (MRL) set by European Regulation for grapes. The proposed method was applied to 17 commercial fortified wines. The analyzed pesticides were not detected in the wines tested.