New methodology for removing carbonyl compounds from sweet wines

Sweet white wines from botrytized grapes present high SO2 levels because of their high sulfur dioxide binding power. The objective of this work was to develop a new method for reducing this binding power by partially eliminating the carbonyl compounds naturally present in these wines that are responsible for this phenomenon. A selective liquid-solid removal technique was developed. Phenylsulfonylhydrazine was selected as the best candidate for removing carbonyl compounds. Its reactivity in the presence or absence of sulfur dioxide was verified in model media containing acetaldehyde, pyruvic acid, and 2-oxoglutaric acid, some of the main carbonyl compounds responsible for the SO2 binding power of sweet wines. The scavenging function was grafted on porous polymer supports, and its efficiency was evaluated in model wines. Dependent upon the supports used, different quantities of carbonyl compounds (over 90% in some cases) were removed in a few days. The presence of sulfur dioxide delayed removal without changing its quality. The results obtained showed that the method removed carbonyl compounds efficiently and was applicable to wines at any stage in winemaking.     

Development of a potentiometric method to measure the resistance to oxidation of white wines and the antioxidant power of their constituents

This work describes a new potentiometric method to evaluate the resistance to oxidation of white wines. Reduction and oxidation titrations were made, and coefficient of variation obtained were 10.87 and 2.65%, respectively. The antioxidant powers of ascorbic acid (Aas) and sulfur dioxide (SO(2)) were evaluated by this method, SO(2) proving to be much less active in this respect than ascorbic acid. The two agents did not demonstrate any antioxidant synergy. A relationship between oxygen present and ascorbic acid was found by the proposed method (1 mmol of O(2) <--> 0.84 mmol of Aas). This method enables the distinction of different wines on the basis of their resistance to oxidation.     

Influence of yeast macromolecules on sweetness in dry wines: role of the saccharomyces cerevisiae protein Hsp12

Yeast autolysis during lees contact influences the organoleptic properties of wines especially by increasing their sweet taste. Although observed by winemakers, this phenomenon is poorly explained in enology. Moreover, the compounds responsible for sweetness in wine remain unidentified. This work provides new insights in this way by combining sensorial, biochemical and genetic approaches. First, we verified by sensory analysis that yeast autolysis in red wine has a significant effect on sweetness. Moderate additions of ethanol or glycerol did not have the same effect. Second, a sapid fraction was isolated from lees extracts by successive ultrafiltrations and HPLC purifications. Using nano-LC-MS/MS, peptides released by the yeast heat shock protein Hsp12p were distinctly identified in this sample. Third, we confirmed the sweet contribution of this protein by sensorial comparison of red wines incubated with two kinds of yeast strains: a wild-type strain containing the native Hsp12p and a deletion mutant strain that lacks the Hsp12p protein (Δ°HSP12 strain). Red wines incubated with wild-type strain showed a significantly higher sweetness than control wines incubated with Δ°HSP12 strains. These results demonstrated the contribution of protein Hsp12p in the sweet perception consecutive to yeast autolysis in wine.     

Role of carbonyl compounds in SO(2) binding phenomena in musts and wines from botrytized grapes

Carbonyl compounds play an important role in musts from botrytized grapes. Some of them, such as glyoxal and methylglyoxal, may explain a considerable part of bindable SO(2). Others, such as 2- and 5-oxogluconic acids, produced by gluconic acid oxidation in proportions respectively from 2.5 per 1 play an interesting role as SO(2) binding indicator. Finally, the levels of some compounds such as dihydroxyacetone, 5-oxofructose, and delta-gluconolactone in balance with gluconic acid are well correlated with SO(2) binding powers and also explain a large part of the bindable SO(2) in musts. During alcoholic fermentation, only dihydroxyacetone among these three compounds is metabolized by yeast. Thus, two compounds present in grapes, delta-gluconolactone and 5-oxofructose, with three yeast SO(2)-binding byproducts, ethanal, pyruvic, and 2-oxoglutaric acids, explain much of the SO(2) binding power in wines from botrytized grapes.     

Influence of storage conditions on the formation of some volatile compounds in white fortified wines (Vins doux naturels) during the aging process

Sweet fortified wines, traditionally aged under strong oxidation conditions, have a characteristic aroma. An experimental study investigated the aging of white sweet fortified wines under various conditions. The development of various molecules, previously identified as characteristic of the aroma of this type of wine, was monitored by analysis. The development of these compounds during accelerated aging was affected by oxidation and the color of the wine. Aging in oak containers, variable storage temperatures, and variable modes of oxidation affect the formation of many of the volatile compounds responsible for the aging aroma of vins doux naturels (fortified wines). Furfural (1), 5-ethoxymethylfurfural (2), and sotolon (3) always reach concentrations above their perception thresholds in wood-aged wines, especially when new oak is used. The isomers of methyl-gamma-octalactone (4 and 5) are reliable indicators of aging in oak. Among the many identifiable volatile phenols, only the vanillin (7) content increases with aging, particularly if the container is made of wood and there is a high degree of oxidation. This molecule frequently reaches and even exceeds its perception threshold. We show here that vanillin and isomers of methyl-gamma-octalactone have a major impact on the aromas of fortified wines.     

Comparative study of polyphenol scavenging activities assessed by different methods

The effect of procyanidin solutions on superoxide anion radicals was studied with an enzymatic method and their EC(50) values were determined. A comparative study of the results suggested that the free radical scavenger potential of these phenolic compounds closely depends on their chemical and stereochemical structures. Oligomeric procyanidins were isolated in different fractions from grapes and wines by low- and high-pressure liquid chromatography. These compounds were found to be efficient free radical scavengers even for the weak concentrations in wines. Their activity in grapes or wines was much stronger than that of other commercially available natural antioxidants (such as ascorbic acid and gallic acid). The effect of tannins isolated from grapes on different radicals was analyzed according to three distinct methods: an enzymatic method for superoxide anion radicals (O(2)(*)(-)), a chemical method for the stable 1,1-diphenyl-2-picrylhydrazyl radical (DPPH(*)), and an immunochemical method to study the scavenging activity of seed procyanidins on DNA lesions induced by the radical HO(*).     

Study of the formation mechanisms of some volatile compounds during the aging of sweet fortified wines.

Sweet fortified wines, traditionally aged under strong oxidation conditions, have a characteristic aroma. An experimental laboratory study investigated the aging of red and white sweet fortified wines under various conditions. The formation of various molecules, previously identified as characteristic of the aroma of this type of wine, was monitored by analysis. The development of these compounds during accelerated aging was affected by oxidation and the color of the wine. Among the molecules studied, sotolon [3-hydroxy-4, 5-dimethyl-2(5H)-furanone] was one of the few molecules present in concentrations above the perception threshold, in both red and white wines. Buildup was strongly affected by the presence of oxygen in white wine subjected to accelerated aging. (Ethoxymethyl)furfural, formed from 5-(hydroxymethyl)furfural, and furfural, derived from sugars, are also involved in the aroma of sweet fortified white wines aged in oxygen-free conditions. The substances most characteristic of accelerated aging of sweet fortified red wines were 5-(hydroxymethyl)furfural, acetylformoin, and hydroxymaltol, the formation of which is affected by oxidation, and dihydromaltol, formed in the absence of oxidation.     

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.     

Changes during storage in conventional and ecological wine: phenolic content and antioxidant activity

Polyphenol content, free radical scavenging capacity, and changes during storage over 7 months in the dark were studied in ecological and conventional red and white wines. In red wines, the most changeable components during storage were the anthocyanins since during storage anthocyanins content decreased 88% in conventional wine and 91% in ecological wine. Initially, the total flavonol contents of the conventional and ecological red wines were 163.88 +/- 2.69 and 153.58 +/- 1.71 mg/L, respectively, and no significant variations occurred during storage. No differences in hydroxycinnamic acid derivatives content between conventional and ecological red and white wines were observed. The flavonol level in white wines was very low, as expected since these compounds are found in grape skin. The initial antioxidant activity was 5.37 +/- 0.14 and 5.82 +/- 0.31 mM equivalents Trolox for conventional and ecological red wines, respectively; no significant differences were observed (p = 0.2831), and these values were 7-8 times higher than the antioxidant activity observed in conventional and ecological white wine. In contrast with other studies, the total concentrations of phenolic compounds in conventional and ecological red and white wines were not related to antioxidant activity (p > 0.05). In red wines, no significant differences were observed in the antioxidant activity of ecological and conventional red wine (p = 0.28), while in white wine significant differences were observed in the antioxidant activity between conventional and ecological white wine (p = 0.006).     

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.     

Phenolic and volatile composition of wines made from Vitis vinifera cv. Muscat lefko grapes from the island of Samos

A study of the phenolic and volatile composition of wines produced from the white cultivar Muscat lefko from the island of Samos was conducted. Dry, fortified, naturally sweet wines and mistelles (aged and nonaged) have been studied. The phenolic components (flavan-3-ols, hydroxycinnamates, and flavonols) were measured by high-performance liquid chromatography after solid phase extraction (SPE). The terpenes (free and glycosidically linked) were determined by the use of gas chromatography-mass spectrometry (GC-MS) after SPE. The fermentation aroma components were analyzed by GC-MS after liquid-liquid extraction. It was found that the dry wines contained lower amounts of most of the phenolics and higher quantities of terpenes and fermentation aroma compounds than the sweet wines. The aged mistelle wines contained lower levels of coutaric and caftaric acids, higher concentrations of the free acids, and markedly fewer free and bound terpenes and fermentation aroma components compared to the other sweet wines. The naturally sweet wine contained relatively increased amounts of phenolics, 2,3-butanediol, and glycosidically linked terpenes.     

Antioxidant activity of South African red and white cultivar wines: free radical scavenging

The free radical scavenging activity of South African red (n = 46) and white (n = 40) cultivar wines was determined using 2,2'-azinobis(3-ethylbenzothialozinesulfonic acid) radical cations (ABTS(.+)) and 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH.). The total antioxidant activities (TAA) of red and white wines using ABTS(.+) were 14.916 and 0.939 mM Trolox, respectively, at corresponding total phenol (TP) contents of 2339.0 and 273.8 mg of gallic acid equiv/L. Ruby Cabernet wines had the lowest TAA(ABTS) (13.177 mM Trolox) of the red wines, whereas the TAA(ABTS) values of Chardonnay and Chenin blanc wines were the highest (1.060 mM Trolox) and lowest (0.800 mM Trolox) of the white wines. The TAA(DPPH) values were of the same magnitude as the TAA(ABTS) values, and similar trends were observed. TAA correlated (P < 0.001) with total phenol content of red (r = 0.935) and white (r = 0.907) wines, as well as flavanol content of red wines (r = 0.866) and tartaric acid ester content of white wines (r = 0.767). Canonical discriminant analysis using phenolic composition and antioxidant activity was applied to differentiate between red and white cultivar wines.     

Antibacterial activity of red and white wine against oral streptococci

Wine contains a number of biologically active compounds with beneficial effects on human health. The antibacterial action of commercial red and white wines against oral streptococci responsible for caries development and against S. pyogenes responsible for pharyngitis was studied. Its postcontact effect against S. mutans was also studied. Both wines displayed activity. The compounds responsible for such activities were succinic, malic, lactic, tartaric, citric, and acetic acid. The synthetic mixtures of the organic acids tested at the concentrations found in wine had greater antibacterial activity than the beverages, indicating that in wine they are inhibited by other components. Wine polyphenols displayed no activity against oral streptococci or S. pyogenes. Findings show that wine is active against oral streptococci and S. pyogenes and suggest that it enhances oral health.     

A powerful aromatic volatile thiol, 2-furanmethanethiol, exhibiting roast coffee aroma in wines made from several Vitis vinifera grape varieties

The chemical compound 2-furanmethanethiol (2FM), with a strong roast coffee aroma, has been identified in sweet white wines made from the Petit manseng grape variety, and in certain red Bordeaux wines (made from the Merlot, Cabernet franc, and Cabernet sauvignon grape varieties). This was done by extracting specific volatile thiols using p-hydroxymercuribenzoate. The 2FM has also been found in toasted oak used in barrel-making. All the Petit manseng sweet white wines and some of the red Bordeaux wines analyzed contained between a few ng/L and several dozen ng/L of 2FM. Taking into account its very low perception threshold (0.4 ng/L in a model hydro alcoholic environment), 2FM could therefore contribute to the roast coffee aroma of certain wines.     

Changes in the sotolon content of dry white wines during barrel and bottle aging

GC-MS in electron ionization mode (EI) was used as a simple, sensitive method for assaying sotolon [4,5-dimethyl-3-hydroxy-2(5) H-furanone] in various dry white wines. The impact of barrel-aging conditions, that is, whether yeast lees were present or not, on the formation of sotolon in dry white wines was then studied. The sotolon content was highest in dry white wines aged in new barrels without lees, often exceeding the perception threshold (8 microg/L). These results demonstrated that yeast lees were capable of minimizing the formation of sotolon in dry white wines during aging. The sotolon and oxygen contents of several bottle of the same white wine were also compared 7 years after bottling. At the range of dissolved oxygen concentrations generally measured, between 5 and 100 microg/L, the sotolon content remained below its perception threshold in wine. The perception threshold was exceeded only in wines with oxygen concentrations above 500 microg/L. The presence of dissolved oxygen in the wine samples analyzed also resulted in a decrease in their free sulfur dioxide content.     

Resistance to oxidation of white wines assessed by voltammetric means

This work concerns the development of a methodology suited to measure the resistance to oxidation of white wines by cyclic voltammetry. The voltammetric responses of several white wines of different origin and age were analyzed in the oxidation potential range (0.2-1.2 V vs SCE). Currents measured at fixed potentials were correlated to the concentration of ascorbic acid, SO2, and total phenolics. A forced degradation study was monitored by cyclic voltammetry; from plots of current versus time, the consumption rates of oxidizable species in wine were estimated.     

Levels of stilbene oligomers and astilbin in French varietal wines and in grapes during noble rot development

Phenolics from grapes and wines can play a role against oxidation and development of atherosclerosis. Stilbenes have been shown to have cancer chemopreventive activity and to protect lipoproteins from oxidative damage. A method for the direct determination of stilbene oligomers (viniferin and pallidol) as well as astilbin in different types of wine using high-performance liquid chromatography with UV detection is described. In a survey of 21 commercial wines from the south of France, levels of pallidol and viniferin are reported for the first time in different types of wines. Viniferin was found to be present only in red and botrytized sweet white wines with levels between 0.1 and 1.63 mg/L; pallidol was not found in dry and sweet white wines but only in wines made by maceration with stems, with levels between 0.38 and 2.22 mg/L. Highest levels of astilbin were found in Egiodola (15.13 mg/L), Merlot (11.61 mg/L), and Cabernet Sauvignon (8.24 mg/L) for red wines and in Sauvignon (5.04 mg/L) for white varietal wines. Astilbin levels are highest for recent vintages, but pallidol is not found in older vintages. During noble rot development in Sauvignon or Sémillon grapes from the Sauternes area, levels of trans-astringin, trans-resveratrol, trans-piceid, and pallidol are quite low (<0.5 mg/kg of grapes). Viniferin and astilbin levels become optimum at 2 and 30 mg/kg, respectively, during spot grape and speckle grape stages.