Influence of some technological parameters on the formation of dimethyl sulfide, 2-mercaptoethanol,methionol, and dimethyl sulfone in port wines

Volatile sulfur compounds of 15 young port wines and 12 old port wines were determined. As there is a great difference in the pool of sulfur compounds between the two groups of wines, an experimental protocol was performed to determine which technological parameter (dissolved O(2), free SO(2) levels, pH, and time/temperature) was related with the formation/consumption of these compounds. Four sulfur compounds were selected for this purpose: dimethyl sulfide, 2-mercaptoethanol, dimethyl sulfone, and methionol. The synergistic effects of increasing temperature and O(2) at lower pH had the largest impact. Dimethyl sulfide was formed during the experimental period in the presence of O(2). Dimethyl sulfone had the same behavior. Methionol decreased significantly in the presence of O(2), but no methional was formed. 2-Mercaptoethanol, considered to be an important "off-flavor" in dry wines, also decreased during the experimental period (54 days) in the presence of O(2), and the respective disulfide was formed. These results corroborate the fact that old port wine (barrel aged) never develops "off-flavors" associated with the presence of methionol (cauliflower), 2-mercaptoethanol (rubber/burnt), or methional (cooked potato). In fact, temperature and oxygen are the major factors in the consumption of these molecules. However, some notes of "quince" and "metallic" can appear during port wine aging, and these can be associated with the presence of dimethyl sulfide.     

Changes in the odorants of boiled carp fillet (Cyprinus carpio L.) as affected by increasing methionine levels in feed

Sixty common carp in groups of five in four tanks per treatment were given three diets containing different increasing amounts of methionine. The aroma extract dilution analysis (AEDA) of the boiled carp fillets resulted in 32 odorants, of which 26 were identified. Ten compounds were quantified using an internal standard (IS), and the very low concentrations of 2-acetyl-1-pyrroline, (Z)-1, 5-octadien-3-one, and methional were calculated by the nasally determined detection limit. The concentration of methional seemed to increase with increasing methionine in the diet. Because the unstable methional could be converted by beta-elimination into methanethiol, the impact resulting in an off-flavor was investigated by headspace analysis. The investigation revealed no difference in the methanethiol contents between the treatments with the lowest and highest methionine supplies.     

Relationship between potentiometric measurements, sensorial analysis, and some substances responsible for aroma degradation of white wines

Oxidative degradation of white wines can be described sensorially as developing from a loss at positive aroma characteristics, through the development of negative aromas to a linel stage of chromatic alterations. This work attempts to relate the oxidation "status" evaluate by potentiometric titrations, with sensorial degradation and the levels of substances responsible for "off-flavors", such as methional and phenylacetaldehyde. The potentiometric titration employed measures the most powerful antioxidants of white wines (e.g., those which more rapidly consume oxygen). Considering that aromatic precedes chromatic degradation, resistance to oxidation (ROX) constitutes a useful indicator of resistance to oxidation. Sensorial degradation (ID), potentiometric measures, and volatiles were determined both in samples submitted to a "forced aging" protocol and normal aged white wines. High correlation values were observed between ROX and the ID, in both sets (r > 0.87). ID is better explained by ROX values than by the indicated wine age or by the "degree of browning" (Abs = 420 nm). It was also observed that in samples with ROX values higher than 10, the concentration of methional and phenylacetaldehyde were above their respective odor threshold. Finally, it was observed that there is a relationship between oxygen consumption and the respective ROX. Although these results seem very promising, they needed to be further complemented in order to estimate the shelf life of a white wine using potentiometric titrations.     

Effect of oxygen on volatile and sensory characteristics of Cabernet Sauvignon during secondary shelf life

The oxidation of Cabernet Sauvignon wines during secondary shelf life was studied by headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-quadrupole mass spectrometry (GC-qMS) and sensory tests, with the support of multivariate statistical analyses such as OPLS-DA loading plot and PCA score plot. Four different oxidation conditions were established during a 1-week secondary shelf life. Samples collected on a regular basis were analyzed to determine the changes of volatile chemicals, with sensory characteristics evaluated through pattern recognition models. During secondary shelf life the separation among collected samples depended on the degree of oxidation in wine. Isoamyl acetate, ethyl decanoate, nonanoic acid, n-decanoic acid, undecanoic acid, 2-furancarboxylic acid, dodecanoic acid, and phenylacetaldehyde were determined to be associated with the oxidation of the wine. PCA sensory evaluation revealed that least oxidized wine and fresh wine was well-separated from more oxidized wines, demonstrating that sensory characteristics of less oxidized wines tend toward "fruity", "citrous", and "sweetness", while those of more oxidized wines are positively correlated with "animal", "bitterness", and "dairy". The study also demonstrates that OPLS-DA and PCA are very useful statistical tools for the understanding of wine oxidation.     

Quality and aromatic sensory descriptors (mainly fresh and dry fruit character) of Spanish red wines can be predicted from their aroma-active chemical composition

A satisfactory model explaining quality could be built in a set of 25 high quality Spanish red wines, by aroma-active chemical composition. The quality of the wines was positively correlated with the wine content in fruity esters, acids, enolones, and wood derived compounds, and negatively with phenylacetaldehyde, acetic acid, methional, and 4-ethylphenol. Wine fruitiness was demonstrated to be positively related not only to the wine content on fruity esters and enolones, but to wine volatile fatty acids. Fruitiness is strongly suppressed by 4-ethylphenol, acetic acid, phenylacetaldehyde, and methional, this involved in the perception of dry-fruit notes. Sensory effects were more intense in the presence of β-damascenone and β-ionone. A satisfactory model explaining animal notes could be built. Finally, the vegetal character of this set of wines could be related to the combined effect of dimethylsulfide (DMS), 1-hexanol, and methanethiol.     

Mousy off-flavor: a review

Although mousy off-flavor occurs infrequently in wine, it can be economically disastrous to the wine producer as, at worst, it can render the wine unpalatable or, at best, decrease the quality of the wine resulting in a lower sale price. Wines infected with either lactic acid bacteria (LAB) (particularly heterofermentative strains) or Dekkera/Brettanomyces yeast can potentially produce mousy off-flavor. There are three known compounds that cause mousy off-flavor: 2-ethyltetrahydropyridine, 2-acetyltetrahydopyridine, and 2-acetylpyrroline. Dekkera/Brettanomyces have been shown to be capable of producing at least two of these compounds, whereas LAB are capable of producing all three. The reason as to why mousy off-flavor forms in some wines and not in others is still not fully understood. The issue is further complicated by the fact that the compounds that have thus far been identified as necessary for off-flavor formation are all potentially available in wine (e.g., ethanol, L-lysine, L-ornithine, and metal ions). For these reasons, the microbe's metabolism probably plays a key role in mousy off-flavor formation. In the case of Dekkera/Brettanomyces-induced mousy off-flavor, it appears that oxygen may play a key role. Thus, a wine infected with Dekkera/Brettanomyces in the absence of oxygen may not become mousy unless exposed to oxygen via a processing or handling procedure.     

Sweet-like off-flavor in Aglianico del Vulture wine: ethyl phenylacetate as the mainly involved compound

Interest in high-quality and peculiar products is a recent trend in the enological field; for this reason, production of wines from autochthonous vine varieties is requested by consumers. Aglianico wine from the Italian region "Basilicata" is an example of a promising product strictly connected to the territory; nevertheless, it is affected by a frequent sweet-like off-flavor. In this study the compositional cause of this off-flavor was investigated by SPME-GC-olfactometry, SPME-GC-MS, and sensory tests. Ethyl phenylacetate (EPhA) was found to be the compound mainly responsible, and its sensory threshold was determined near 73 microg/L; products with the odorant concentration near and up to these values were always recognized as significantly different from the other wines and were often far from wine technical pleasantness; besides EPhA gave to the wines a strong honey-like character. Some preliminary hypotheses about its mechanism of formation (shikimate pathway) are presented in this study: these hypotheses could explain the correlation between EPhA and volatile phenols that was found by both sensory tests and GC quantitative analysis of wines affected by different levels of defect.     

New qualitative approach in the characterization of antioxidants in white wines by antioxidant free radical scavenging and NMR techniques

The aim of this study was to obtain new information on antioxidant compounds in white wines. For this purpose, white wine degradation was promoted by a forced aged protocol, and six normally aged white wines from different vintages were analyzed. Both normal and forced aged wines were sequentially extracted using hexane and ethyl acetate. Apolar antioxidants were removed using hexane, and polar antioxidants were extracted with ethyl acetate. This last residue was subject to partial re-extraction with hexane and acetone. The antioxidant capacity of the wines and of each fraction was evaluated by two free radical methods, ABTS and DPPH. Normal aging provides a decrease in the total antioxidant capacity of wines. The antioxidant activity of ethyl acetate/acetone extracts was approximately 95% higher than that found for the hexane extracts. Concerning the forced aged wines, results showed that the wine submitted to a temperature of 60 degrees C for 21 days had higher antioxidant activity than that submitted to a temperature of 20 degrees C. With regard to the ethyl acetate/acetone extracts, oxygen and temperature treatment leads to a decrease in their antioxidant activity. NMR analysis was performed in the highest antioxidant capacity organic fractions (ethyl acetate/acetone extracts) and in the aqueous fraction of the control wine (T = 20 degrees C), in order to attempt the characterization of species involved in oxygen protection. Possible structures of antioxidant compounds in white wines were proposed. Two of these are tyrosol-like structures. This molecule is a well-known phenolic compound in wine, and it is reported to have antioxidative effects.     

Characterization of aroma-active compounds in rainbow trout (Oncorhynchus mykiss) eliciting an off-odor

The aroma-active and off-flavor compounds of cooked rainbow trout (Oncorhynchus mykiss) were analyzed by sensory and instrumental analyses. Sensory analysis shows that the aromatic extract obtained by vacuum steam distillation was representative of rainbow trout odor. To obtain more information on odorants of volatile compounds, analyses were conducted on two gas chromatography columns of different polarities (DB-5 and DB-Wax). The results of the gas chromatography-olfactometry analysis showed that 38 odorous compounds were perceived when the DB-5 column was used and 36 with the DB-Wax column. Of these, 31 with the DB-5 and 28 with the DB-Wax were identified. (E)-2-Nonenal, 2-ethyl-1-hexanol, 2-methylisoborneol, geosmin, 2-methylnaphthalene, and 8-heptadecene were described as off-flavor compounds by the sniffing assessors. The most powerful off-flavor compounds identified in the extract were 2-methylisoborneol and geosmin, which were described as strong musty and earthy odors, respectively.     

An assessment of the role played by some oxidation-related aldehydes in wine aroma

The levels of important oxidation-related aldehydes, such as methional, phenylacetaldehyde, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, methylpropanal, 2-methylbutanal, and 3-methylbutanal, were determined in 41 different wines belonging to different types (young whites and reds, natural sparkling wines, oxidized young whites and reds, Sherry, aged red wines, Port wines). Except (E)-2-hexenal and (E)-2-heptenal, all of them could be found at levels above threshold. Different compositional patterns were identified: Sherry wines have large amounts of branched aldehydes but not of (E)-2-alkenals, wines exposed to oxygen can have large amounts of (E)-2-alkenals but not of branched aldehydes, while aged wine and Port have relatively large amounts of both classes of compounds. Different sensory tests confirmed the active sensory role of these compounds and revealed the existence of interactions (additive or synergic) between them and with other wine volatiles. (E)-2-Alkenals are related to flavor deterioration, while branched aldehydes enhance dried fruit notes and mask the negative role of (E)-2-alkenals.     

The role of lysine amino nitrogen in the biosynthesis of mousy off-flavor compounds by Dekkera anomala

Mousy off-flavor is an insidious and economically disastrous microbiologically derived spoilage characteristic of wine and other fermented beverages. Tainted wines are rendered unpalatable and there is currently no satisfactory procedure for removal of the off-flavor. Here we report the confirmation of that both d- and l-lysine can act as a precursor for the formation of mousy off-flavor N-heterocycles. Further, through the use of stable isotope feeding experiments, we could establish that a pentylamine group from lysine is incorporated into the piperideine moiety of two off-flavor N-heterocycles. A biochemical pathway for the formation of mousy off-flavor compounds is proposed.     

Isolation and characterization of a thermally extracted yeast cell wall fraction potentially useful for improving the foaming properties of sparkling wines

Two different yeast cell wall extracts were obtained using enzymatic digestion and thermal treatment. The effects of the extracts obtained on the foaming properties of a model wine and two sparkling wines were studied. The model wine and sparkling wines, supplemented with the thermal extract, presented better foaming properties than did the samples supplemented with the enzymatic extract. The fractioning (Con A chromatography) and characterization (SDS-PAGE, SEC, GC, and RP-HPLC) of both extracts showed that the fraction responsible for the foaming properties is constituted by mannoproteins with a relative molecular weight between 10 and 30 kDa, presenting an equilibrated composition of the hydrophobic and hydrophilic protein domains. This thermal extract did not modify the protein stability in both the model wine and the sparkling wines. These results demonstrate that the enrichment of a sparkling wine with mannoproteins extracted by mild heat procedures will contribute to improving its foaming properties.     

Synergistic effect of high and low molecular weight molecules in the foamability and foam stability of sparkling wines

The foam of sparkling wines is a key parameter of their quality. However, the compounds that are directly involved in foam formation and stabilization are not yet completely established. In this work, seven sparkling wines were produced in Bairrada appellation (Portugal) under different conditions and their foaming properties evaluated using a Mosalux-based device. Fractionation of the sparkling wines into four independent fractions, (1) high molecular weight material, with molecular weight higher than 12 kDa (HMW), (2) hydrophilic material with molecular weigh between 1 and 12 kDa (AqIMW), (3) hydrophobic material with molecular weigh between 1 and 12 kDa (MeIMW), and (4) hydrophobic material with a molecular weight lower than 1 kDa (MeLMW), allowed the observation that the wines presenting the lower foam stability were those that presented lower amounts of the MeLMW fraction. The fraction that presented the best foam stability was HMW. When HMW is combined with MeLMW fraction, the foam stability largely increased. This increase was even larger, approaching the foam stability of the sparkling wine, when HMW was combined with the less hydrophobic subfraction of MeLMW (fraction 3). Electrospray tandem mass spectrometry (ESI-MS/MS) of fraction 3 allowed the assignment of polyethylene glycol oligomers (n = 5-11) and diethylene glycol 8-hydroxytridecanoate glyceryl acetate. To observe if these molecules occur in sparkling wine foam, the MeLMW was recovered directly from the sparkling wine foam and was also analyzed by ESI-MS/MS. The presence of monoacylglycerols of palmitic and stearic acids, as well as four glycerylethylene glycol fatty acid derivatives, was observed. These surface active compounds are preferentially partitioned by the sparkling wine foam rather than the liquid phase, allowing the inference of their role as key components in the promotion and stabilization of sparkling wine foam.     

Polyphenol compounds and anti-inflammatory activities of Korean black raspberry ( Rubus coreanus Miquel) wines produced from juice supplemented with pulp and seed

Three types of Korean black raspberry wine were produced via alcoholic fermentation from juice, juice-pulp, and juice-pulp-seed, respectively. These wines were compared in terms of their anti-inflammatory activities and polyphenol contents. The total content of polyphenol compounds in wines was increased by 22.4% after supplementation with pulp and by 56.7% after supplementation with both pulp and seed. The reduction rate of NO evolution was highest in the order juice-pulp-seed wine, juice-pulp wine, and juice wine. Addition of the juice-pulp-seed wine at a level of 62.5-500 mg/L decreased the NO evolution rate by 40.5-94.2%. Eight fractions were obtained from juice-pulp-seed wine via ethyl acetate extraction and silica gel chromatography. Of these, the AF fraction, which exhibited the highest in vitro anti-inflammatory activity, exerted inhibitory effects on ear edema, writhing response, and vein membrane vascular permeability in mice. 3,4-Dihydroxybenzoic acid accounted for 37.6% of the total polyphenol content in the AF fraction.     

White wine continuous protein stabilization by packed column

Protein stabilization is an important stage in the production of white wine. This paper studies white wine protein stabilization using a continuous process with zirconium oxide (powder and pellets) packed in a column. The results show that the total proteins decrease by 50 and 70% for the pellet and powdered zirconium oxides, respectively. Treatment with all zirconium oxides improves wine stability. The effect of the heat regeneration process on both zirconium oxide forms is to increase the adsorption capacity. The wine treated with powdered zirconium oxide after the regeneration is the most effective for preventing protein haze. The protein profile of wine after treatment shows that the 20-50 kDa and 50-70 kDa fractions are the ones removed preferentially, while the 15 kDa fraction and the ones higher than 70 kDa are removed the least. The results show that the protein fraction with a molecular weight of 15 kDa does not affect the protein instability of the wines studied. The protein fraction with a molecular weight higher than 70 kDa seems to influence protein instability. The physicochemical properties of wine after treatment were not affected, and the values obtained were like those of the standardized range.     

A novel method for quantification of 2-methyl-3-furanthiol and 2-furanmethanethiol in wines made from Vitis vinifera grape varieties

A rapid, easy method has been developed for isolating and quantifying 2-methyl-3-furanthiol (2M3F) in wines. Until now, it was not possible to quantify this highly odoriferous compound, with a smell reminiscent of cooked meat, in wine. The original aspect of this method is the specific release of volatile thiols using a cysteamine solution applied in reverse flow to sample percolation on the basis of a p-hydroxymercuribenzoate (pHMB)-volatile thiol conjugate formed by the direct addition of pHMB to 50 mL of wine. Purification of volatile thiols in wines is much faster and easier than our previous method. This method may also be used to assay 2-furanmethanethiol in wine. This thiol's strong aroma of roasted coffee has been shown to contribute to the "roast coffee" aroma of certain wines. Assaying 2M3F by this method showed that it was present in the wines analyzed (red and white Bordeaux, Loire Valley Sauvignon blanc, white Burgundy, and Champagne) at concentrations up to 100 ng/L, i.e., significantly above the olfactory perception threshold for this compound in model dilute alcohol solution.     

Distribution and organoleptic impact of sotolon enantiomers in dry white wines

The enantiomers of sotolon, a flavor compound typical of oxidized white wines, were separated by preparative HPLC to determine their perception thresholds and distribution in wines. The enantiomeric ratios of chiral sotolon were evaluated in several dry white wines using gas chromatography and a chiral column (beta-cyclodextrin) connected to a 2 m precolumn (BP20). The perception threshold of (S)-sotolon (0.8 microg/L) in model wine solution was 100 times lower than that of the (R) form (89 microg/L), indicating that (S)-sotolon contributes to the characteristic aroma of prematurely aged dry white wines. Both enantiomers are detected in white wines. Analysis of commercial dry white wines from various vintages and origins revealed three types of distribution patterns: the racemic form, an excess of R, and an excess of S. The proportions found in these wines may be partially explained by the slow racemization kinetics (20 months) of optically active sotolon.     

Foamability and foam stability of molecular reconstituted model sparkling wines

The present work aims at identifying the contribution of the different wine components to the foaming properties of wines. Twelve fractions were isolated from wine, and foam aptitude of each fraction was measured individually at the concentration at which it was recovered, using wine model solutions. For these concentrations, the maximum foam height (HM) was 8.4-11.7 cm, foam height on stability was 6.9-7.5 cm, and foam stability (TS) was 3.0-6.5 s. Moreover, foam measurements were also performed using 2-, 5-, and 10-fold concentrations of these compounds in wine. The HM increased linearly with the concentration of mannoproteins having low content of protein (MP1), and TS increased exponentially. The fractions that individually showed higher foaming properties were mixed in binary and ternary combinations, demonstrating that MP1 when mixed with low molecular weight hydrophobic compounds strengthens the air/water interface of these solutions, a characteristic that is on the basis of sparkling wines' foamability and foam stability.     

Effect of macerating enzymes on the oligosaccharide profiles of Merlot red wines

Commercial pectinase preparations are applied in winemaking to improve wine processing and final quality. These preparations contain pectolytic enzyme activities such as polygalacturonases, pectin esterases, pectin lyases, and rhamnogalacturonases. These enzymes modify the polysaccharide and oligosaccharide composition of wines. The influence of various commercial enzyme preparations on wine oligosaccharide composition was studied, on Merlot wines from the Bordeaux area. Wine oligosaccharides were isolated by high-resolution size-exclusion chromatography on a Superdex-30 HR column. The glycosyl residue and glycosyl linkage compositions of the oligosaccharide fractions obtained were determined. The MS spectra of the Merlot oligosaccharide fractions from control and enzyme-treated wines were recorded on an AccuTOF mass spectrometer equipped with an electrospray ionization (ESI) source and a time-of-flight (TOF) mass analyzer. Oligosaccharides in the control wines were partly methylated homogalacturonans, corresponding to smooth regions of pectins, whereas those of the enzyme-treated wines were mostly rhamnogalacturonan-like structures linked with neutral lateral chains, arising from the hairy regions. The enzyme preparations used thus cleaved the rhamnogalacturonan backbone of the hairy zones and demethylated and hydrolyzed the smooth regions. Besides, different structures were detected, depending on the enzyme preparation used, indicating that they contained rhamnogalacturonase activities with different specificities. The oligosaccharide profiles can serve as a marker of enzymatic treatments.     

Identification and sensory evaluation of volatile compounds in oxidized porcine liver

Headspace solid phase microextraction (HS-SPME) was used to isolate the off-flavor volatile compounds, which are formed during the oxidation of porcine liver induced by iron. Poly(dimethylsiloxane)/divinylbenzene fiber was used in the HS-SPME. Changes in the volatile compounds of oxidized porcine liver and unsaturated fatty acids induced by iron were examined. Results showed that 1-octen-3-one (metallic), hexanol (weak metallic), 1-octen-3-ol (mushroomlike), (E)-2-nonenal (cardboardlike), and (E,E)-2,4-decadienal (fatty, oily) were the main contributors to the overall off-flavor of porcine liver. The results of the sensory evaluation revealed that oxidized arachidonic acid has a major impact on metallic and liverlike off-flavor and that when liverlike off-flavor is perceived, metallic is also included. Oxidized linolenic acid was the most important contributor to the objectionable fishy off-flavor. Oxidized porcine liver exhibited distinct metallic, liverlike, and weak fishy background notes. Liverlike flavor had a high correlation coefficient with odor characteristics such as metallic (0.839) and fishy (0.777). In this study, it was clearly observed that the stronger the metallic and fishy off-flavor the higher the perception of liverlike off-flavor.