Yeast-induced inhibition of (+)-catechin and (-)-epicatechin degradation in model solutions

(+)-catechin and (-)-epicatechin degradation in water-alcohol solutions containing Fe2+ and tartaric acid was studied in the presence and absence of yeasts. On the basis of the results, yeast partially inhibited the degradation of both flavans, with much slower formation of browning products absorbing at 420 and 520 nm. In comparative terms, yeast was found to be more efficient toward the degradation products of (+)-catechin absorbing at the latter wavelength. Likewise, the presence of yeast decreased the yield of a group of colored compounds eluting at high retention times in HPLC and indicated these as important contributors to color darkening in white wines. This inhibitory effect may in part account for the resistance to browning observed over periods of several years in sherry wines subjected to biological aging under flor yeast.     

Phenolic compounds and browning in sherry wines subjected to oxidative and biological aging

The composition in hydroxybenzoic and hydroxycinnamic acids, hydroxycinnamic esters, tyrosol, syringaldehyde, and flavan-3-ol derivatives of three different types of sherry wine obtained by aging of the same starting wine under different conditions was studied. So-called "fino" wine was obtained by biological aging under flor yeasts, "oloroso" wine by oxidative aging, and "amontillado" wine by a first stage of biological aging followed by a second oxidative step. On the basis of the results, the wines subjected to oxidative aging exhibited higher phenol contents, in addition to scarcely polar compounds absorbing at 420 nm that were absent in the wines obtained by biological aging. Taking into account that flavan-3-ol derivatives play an important role in wine browning, a model catechin solution was inoculated with flor yeast which, contrary to the findings of other authors in the absence of yeasts, formed no colored compounds. This different behavior may account for the resistance to browning of pale sherry wines in the presence of flor yeasts.     

Antioxidant action of glutathione and the ascorbic acid/glutathione pair in a model white wine

Glutathione was assessed individually, and in combination with ascorbic acid, for its ability to act as an antioxidant with respect to color development in an oxidizing model white wine system. Glutathione was utilized at concentrations normally found in wine (30 mg/L), as well as at concentrations 20-fold higher (860 mg/L), the latter to afford ascorbic acid (500 mg/L) to glutathione ratios of 1:1. The model wine systems were stored at 45 °C without sulfur dioxide and at saturated oxygen levels, thereby in conditions highly conducive to oxidation. Under these conditions the results demonstrated the higher concentration of glutathione could initially provide protection against oxidative coloration, but eventually induced color formation. In the period during which glutathione offered a protective effect, the production of xanthylium cation pigment precursors and o-quinone-derived phenolic compounds was limited. When glutathione induced coloration, polymeric pigments were formed, but these were different from those found in model wine solutions without glutathione. In the presence of ascorbic acid, high concentrations of glutathione were able to delay the decay in ascorbic acid and inhibit the reaction of ascorbic acid degradation products with the wine flavanol compound (+)-catechin. However, on depletion, the glutathione again induced the production of a range of different polymeric pigments. These results highlight new mechanisms through which glutathione can offer both protection and spoilage during the oxidative coloration of a model wine.     

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.     

Identification of 4-methylspinaceamine, a pictet-spengler condensation reaction product of histamine with acetaldehyde, in fermented foods and its metabolite in human urine

Previous study demonstrated that 4-methylspinaceamine (4-methyl-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine), a Pictet-Spengler condensation reaction product of histamine with acetaldehyde, is present in human urine. The current study sought to determine whether 4-methylspinaceamine is present in fermented foods; its presence might be expected since both histamine and acetaldehyde are often present in these foods. Soy sauce, fish sauce, cheese, and shao hsing wine (Chinese wine) were found to contain 4-methylspinaceamine. The concentration of 4-methylspinaceamine excreted in human urine was greatly elevated after ingestion of a meal containing soy sauce as a dietary source of 4-methylspinaceamine, demonstrating that the level of 4-methylspinaceamine in human urine was affected by dietary foods. In addition, a metabolite of 4-methylspinaceamine in human urine was investigated. An enhanced peak in the HPLC chromatogram of human urine samples after ingestion of 4-methylspinaceamine-containing foods was observed. A peak at the same retention time was also observed from a human urine sample after administration of 4-methylspinaceamine, suggesting that the peak was due to a metabolite. By comparison with the newly synthesized authentic compound, the metabolite was identified as 1,4-dimethylspinaceamine.     

Heterocyclic acetals from glycerol and acetaldehyde in Port wines: evolution with aging

In Port wine, isomers of glycerol and acetaldehyde acetals have been found at total contents ranging from 9.4 to 175.3 mg/L. During oxidative aging, the concentrations of the 5-hydroxy-2-methyl-1,3-dioxane and 4-hydroxymethyl-2-methyl-1,3-dioxolane isomers increased with time showing a linear correlation (r > 0.95). The flavor threshold for the mixture of the four isomers was evaluated in wine at 100 mg/L. Thus, it is expected that they contribute to "old Port wine" aroma in wines older than 30 years. Experiments with model solutions and wine clearly demonstrated that SO(2) combines with acetaldehyde and blocks the acetalization reaction.     

Impact of oxygen consumption by yeast lees on the autolysis phenomenon during simulation of wine aging on lees

Potential oxygen consumption by lees, more precisely by nonviable yeasts, during wine aging was recently described. Additionally, yeast autolysis is described as the main mechanism of degradation of lees during wine aging. Thus, to understand the effect of oxygen consumption by yeast lees during wine aging, an accelerated wine aging methodology was tested. Wine aging in the presence of yeast lees was studied both in the presence and in the absence of oxygen. Different markers of yeast autolysis were followed to find a relationship between oxygen consumption by yeast lees and changes in the final wine composition after aging. No differences for compounds tested were found in the wine and in the lees except among sterol compounds in lees: in the presence of oxygen, the concentration of ergosterol in lees was significantly lower than that in the absence of oxygen. It was hypothesized that ergosterol could be oxidized under the influence of oxygen, but none of the known products of ergosterol oxidation were recovered in the corresponding yeast lees. In addition, the decrease of ergosterol content in yeast lees cannot account for the total amount of oxygen consumed by yeast lees during such wine aging.     

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.     

Influence of blending on the content of different compounds in the biological aging of sherry dry wines

Principal components analysis to examine the effect of blending (viz. the mixing and transfer of wine between cask rows in a "criaderas and solera" system) on metabolic activity in flor yeasts during biological aging of sherry dry wines was carried out. The variables used in the analysis were the wine compounds most deeply involved in the flor yeast metabolism, namely ethanol, acetaldehyde, glycerol, acetic acid, and l-proline. The greatest blending effect was found to be on the third and second "criadera", which are the stages where the yeasts show a high metabolic activity. The stages holding the oldest wine (viz. the first criadera and the solera) exhibited no differences before and after blending; therefore, the yeasts have a decreased biological activity in them and physical-chemical aging processes seemingly prevail over it.     

Use of dehydrated waste grape skins as a natural additive for producing rosé wines: study of extraction conditions and evolution

Dehydrated waste grape skins from the juice industry were used as an additive to produce rosé wines. Maceration time, particle size, dosage, alcoholic content, and maceration temperature were first studied in model wine solutions using two different dehydrated waste grape skins. Full factorial experimental designs together with Factor Analysis and Multifactor ANOVA allowed for the evaluation of each parameter according to the composition of color and phenolic and aroma compounds. Higher maceration time favored the extraction of anthocyanins; phenolic compound release was influenced by dosage independent from other factors studied. Rosé wines were produced by direct addition of dehydrated waste grape skins, according to selected parameters in two different white wines, achieving characteristics equivalent to commercial rosé wines. After three months of storage, rosé wine composition was stable.     

Adsorption of phenolic compounds and browning products in white wines by yeasts and their cell walls

Dehydrated yeast cells at variable concentrations were used as fining agents to decrease the color of white wines with two different degrees of browning (0.153 and 0.177 au, measured at 420 nm). Both wines showed a linear decrease of browning with increasing yeast concentration. However, in terms of efficiency, the yeasts exhibited a higher color lightening at greater concentrations acting on the darker wine. This suggests a preferential retention of some types of yellow-brown compounds that could increase their concentrations at the higher degree of browning. To confirm the role of yeast cell walls in the retention of browning compounds and to evaluate their potential use as fining agents, they were applied at variable concentrations to a browned wine (0.175 au). The cell walls were found to be the active support for the adsorption of browning compounds, but their efficiency was much lower than that of an equivalent amount of the yeast cells from which they were obtained. Finally, HPLC determinations of low-molecular-weight phenolic compounds showed flavan-3-ol derivatives to be significantly retained by both yeasts and their cell walls.     

Inhibition of trypsin by condensed tannins and wine

Phenolic compounds are abundant vegetable secondary metabolites in the human diet. The ability of procyanidin oligomers and wine polyphenols to inhibit trypsin activity was studied using a versatile and reliable in vitro method. The hydrolysis of the chromogenic substrate N-benzoyl-d,l-arginine-p-nitroanilide (BApNA) by trypsin was followed by spectrophotometry in the presence and absence of condensed tannins and wine. A clear relationship between the degree of polymerization of procyanidins and enzymatic inhibition was observed. Trypsin activity inhibition was also detected in several types of wine. In general, the inhibition increased with the concentration of phenolic compounds in wines. These results may be relevant when considering these compounds as antinutritional factors, thereby contributing to a reduced absorption of nutrients.     

New method for reducing the binding power of sweet white wines

Sulfur dioxide is now considered to be a toxic chemical by most world health authorities. However, it remains an irreplaceable additive in enology for wine conservation, combining antioxidant and antibacterial properties. Sweet white wines from botrytized grapes retain particularly high SO 2 levels due to their high sulfur dioxide binding power. This paper presents a new method for reducing this binding power by removing some of the carbonyl compounds responsible, which are naturally present in these wines. The main carbonyl compounds responsible for the SO 2 binding power of sweet wines were removed, that is, acetaldehyde, pyruvic acid, 2-oxoglutaric acid, and 5-oxofructose. The method retained was selective liquid-solid removal, using phenylsulfonylhydrazine as a scavenging agent. The scavenging function was grafted on different classes of porous polymer supports, and its efficiency was evaluated on sweet white wines under conditions intended to conserve their organoleptic qualities. The results obtained showed that the method was efficient for removing carbonyl compounds and significantly reduced the binding power of the wines. Sensory analysis revealed that this process did not deteriorate their organoleptic qualities.     

Studies on the acetaldehyde-induced condensation of (-)-epicatechin and malvidin 3-O-glucoside in a model solution system.

The reaction between (-)-epicatechin, malvidin 3-O-glucoside, and acetaldehyde was studied in a model solution system. Ethyl-linked flavanol oligomers and anthocyanin-flavanol derivatives were observed, showing that the two polyphenols competed in the condensation process. Among the anthocyanin-ethyl-flavanol adducts, dimeric compounds in which the flavanol was linked to the anthocyanin with CH(3)-CH bridges were observed. In addition, trimeric and tetrameric products containing one anthocyanin and one, two, or three flavanols units were detected. A tetrameric product containing two anthocyanin and two flavanol units was also found as a doubly charged ion. No compound containing more than two malvidin 3-O-glucosides was detected, suggesting that only one anthocyanin A ring summit can be included in the polymerization process, which thus stops when both ends are occupied by an anthocyanin moiety. Thioacidolysis of the two isolated anthocyanin-ethyl-flavanol dimeric derivatives showed that anthocyanin-ethyl linkage was not sensitive to such reactants, whereas the flavanol-ethyl one was. In addition, flavanol-ethyl linkages involved in anthocyanin-ethyl-flavanol adducts were found to be less sensitive to those involved in flavan-ethyl dimers.     

Effect of different lysis treatments on the characteristics of yeast derivatives for winemaking

The effects of three preparation techniques on the oenological properties of a yeast autolysate were investigated: enzymatic autolysis, thermolysis, and the combination of a slow freezing-defrosting and mechanical disruption were carried out on a commercial formulation of active dry yeasts (Saccharomyces cerevisiae). The powders obtained by freeze drying, were characterized: volatile compounds were analyzed by SPME-GC with mass spectrometric (MS) and olfactometric detection (O); the release of colloids in winelike solution was studied by SDS-PAGE and size exclusion chromatography (SEC). Finally, the effects of the powders addition on the aroma composition of a white wine were investigated by SPME-GC-MS, SPME-GC-O, and sensory evaluation. The products obtained were quite different from each other. In particular, enzymatic autolysis led to higher contents of nonglycosilated soluble proteins in the powders and determined a higher retention of wine aroma compounds. On the contrary, thermal autolysate was richer in glycoproteins, and it was able to increase the wine aroma intensity; nevertheless, in the wines treated with such preparation, a slight yeastlike olfactory note was perceived.     

Changes in nitrogen compounds in must and wine during fermentation and biological aging by flor yeasts.

Urea, ammonium, and free amino acid contents were quantified in a must from Vitis vinifera cv. Pedro Ximenez grapes and in fermented wine and after a short aging of this wine by Saccharomyces cerevisiae race capensis yeast under variable oxygen availability conditions. The previous compounds were also determined in a wine in which the nitrogen source was depleted by the same race of flor yeast (old wine) and also following the addition of ammonium ion, L-glutamic acid, and L-proline. Under specific conditions such as low oxygen level and the absence of some nutrients, the yeasts release some amino acids including L-threonine, L-tryptophan, L-cysteine, and L-methionine to the medium. These amino acids must originate primarily in a de novo synthesis from ethanol that regenerates NAD(P)+. On the basis of these results, the yeasts may be able to use amino acids not only as nitrogen sources but also as redox agents to balance the oxidation-reduction potential under conditions of restricted oxygen, when electron transport along the respiratory chain may be hindered or limited.     

Influence of procyanidins on the color stability of oenin solutions

The aim of the present work was to specify the influence of the polymerization degree on the color stability of anthocyanins using model solutions under higher thermal conditions simulating rapid food aging. Results showed that an increase in polymeric degree improves the color stability of oenin. Solutions containing a catechin tetramer, purified from brown rice, displayed a remarkable stability. Flavanols as monomers, (+)-catechin and (-)-epicatechin, appeared to decrease stability with the formation of a xanthylium salt leading to yellowish solutions. For the dimers, procyanidin B2 and B3, different behaviors on red color stability have been observed corresponding to their different susceptibility to cleavage upon heating. In the presence of the trimeric procyanidin C2, the red color appeared more stable. However, the HPLC chromatograms showed a decrease in the amplitude of the peaks of oenin and procyanidin C2. Concomitantly, a new peak appeared with a maximal absorption in the red region. This newly formed pigment probably came from the condensation of oenin and procyanidin C2.     

Influence of different phenolic copigments on the color of malvidin 3-glucoside

The effectiveness of seven phenolic compounds (catechin, epicatechin, procyanidin B2, caffeic acid, p-coumaric acid, myricitrin, and quercitrin) as copigments of malvidin 3-glucoside, the major anthocyanin in red wines from Vitis vinifera, using a copigment/pigment molar ratio of 1:1 was assayed in model wine solutions under the same conditions (pH=3.6, 12% ethanol). The stability of the copigment-pigment complexes formed was studied during a storage period of 60 days at 25 degrees C. Tristimulus colorimetry was applied for color characterization of the copigmentation process, and HPLC-DAD-MS was used to monitor changes in the composition of the samples. Copigmentation has been found to occur in all cases despite the low copigment/pigment molar ratio used, although the effect was different depending on the compound. Flavan-3-ols appeared as the less effective copigments, procyanidin B2 being even worse than monomeric flavanols, whereas flavonols behaved as the best ones. These latter copigments also induced the most statistically significant bathochromic shift in lambdamax. In the colorimetric analysis, it was observed that the lightness L* of the copigmented solutions increased with time, chroma C*ab decreased, and the hue hab increased. The copigments that produced a greater increase in the hue angle were the monomeric flavan-3-ols, which therefore showed to be the least protective cofactors against browning of the anthocyanin solution during the storage. With the time of storage, the formation of new pigments was observed in the solutions containing flavanols (xanthylium structures) and hydroxycinnamic acids (pyranoanthocyanins), which explains some of the color modifications produced in these solutions. Another relevant observation was that the stability of the anthocyanin was not much improved by most of the assayed copigments, since quite similar degradation rates were observed in the presence and absence of those cofactors.     

Role of vinylcatechin in the formation of pyranomalvidin-3-glucoside-+-catechin

Reactions between malvidin-3-glucoside (mv3glc) and 8-vinylcatechin were carried out to synthesize pyranomv3glc-(+)-catechin pigment and to study the formation of intermediates. A rapid decrease of mv3glc content concomitant with the formation of more complex structures such as mv3glc-vinylcatechin [precursor of pyranomv3glc-(+)-catechin pigment] and mv3glc-divinylcatechin was observed. On the other hand, 8-vinylcatechin undergoes acid-catalyzed dimerization in model wine solution, giving rise to 8-vinylcatechin dimers. These compounds were also found in the reaction between mv3glc and (+)-catechin mediated by acetaldehyde, which provides evidence for the formation of 8-vinylcatechin and its involvement in the formation of pyranoanthocyanins in aged red wines.     

Concurrent phenomena contributing to the formation of the aroma of wine during aging in oak wood: an analytical study

Red wine was stored in different oak barrels or in stainless steel, and samples were taken for two years to determine 79 aroma compounds. Aging in oak affects 41 compounds. The type of wood affects 11 compounds. At least seven different processes seem to take place concurrently in aroma evolution, and five such processes, affecting 37 compounds, are linked to the oak cask. These are extraction from the wood, oxidation of wine alcohols and amino acids, microbiological formation of ethyl phenols, sorption processes, and condensation of acetaldehyde with polyphenols. The wood can release linear gamma- and delta-lactones, beta-damascenone, and ionones. Some compounds are released very fast from wood, which suggests they lie in the external part of the wood. Some extraction profiles are too complex to be explained by physical processes. Finally, the levels of 2,5-dimethyl-4-hydroxy-3(2H)-furanone and 2-ethyl-5-methyl-4-hydroxy-3(2H)-furanone increase even in the reference wine, which suggests the presence of a precursor.