Aroma compounds and sensory characteristics of Arneis Terre Alfieri DOC wines: the concentration of polyfunctional thiols and their evolution in relation to different ageing conditions
arneis is a white wine grape cultivar grown mainly in Pied-mont, in northwest Italy. The production of arneis wines is regulated by three different Controlled Designation Of origin (DOC), namely Langhe Arneis (DOC), Roero Arneis (DOCg) and Terre Alfieri Arneis (DOC). These three denominations are located in the most suitable viticultural areas in Piedmont: Roero and Colline Alfieri, on the left side of the Tanaro river and Langhe, the hilly region that extends to the orographic right of that river. The production of this wine continues to rise and, in 2010, reached, only for the main denomination Roero Arneis, a cultivated area of approximately 7 km2 with a pro-duction of over 39.000 hl. (data from “Consorzio di Tutela Barolo Barbaresco alba langhe e Roero”); besides being an autochthonous grape variety, the interest in arneis grapes and wines is increasing in overseas regions, such as new Zealand, australia, California and Oregon [1]. Despite the growing export and significant economic interest, chemical profile of this native variety, with particular regard to the characteristic aroma composition, is largely unknown.
The sensory evaluation of arneis wines often exhib-its fruity notes with noticeable tropical fruits, passion fruit, grapefruit and sage, especially during the first month after the end of alcoholic fermentation (aF). However, no correla-tion had been made until now between these olfactory char-acteristics and the chemical composition of arneis wine.
Many different compounds are involved in wine aroma characterization, covering a wide concentration range vary-ing between mg l−1 to the ng l−1 level [2]. Moreover, sev-eral chemical classes of molecules, such as hydrocarbons,
Abstract arneis is an Italian autochthonous white grape cultivar. This study involved investigating the chemicophysi-cal, aromatic composition and sensory evaluation of arneis wine in relation to different oenological practices during win-emaking and ageing. For the first time, polyfunctional thiols related aromas were identified above their perception thresh-old in arneis wine. Moreover, citrus, grapefruit and tropical fruit notes characterized this wine during the first month of ageing, thus suggesting a strong correlation between chemical and sensory results. The concentration of thiols decreased rap-idly during the first month of ageing, together with the tropical fruit notes. In particular, the perception of the grapefruit note of the wine decreased in association with the 3-mercaptohexyl acetate content in both the barrel and stainless steel (ST) aged wines. Moreover, the ageing technique clearly affected wine composition and sensory profile; barrel aged wines were char-acterized both by vanilla and honey notes, and a weaker per-ception of thiols despite containing a similar concentration to ST aged wines. Within this study, the ability of glutathione to decrease the oxidation of volatile thiols in arneis wine was confirmed, but under experimental conditions employed, the addition of reduced glutathione did not lead to any statistically significant differences in sensory results.
F. Piano · M. Petrozziello (*) · E. Vaudano · F. Bonello Consiglio per la Ricerca e Sperimentazione in agricoltura, Centro di Ricerca per l’Enologia, Via P. Micca 35, asti, Italye-mail: [email protected]
V. Ferreira · J. Zapata · P. Hernández-Orte Departamento de Química analítica, Universidad de Zaragoza, Calle Pedro Cerbuna 12, 50009 Saragossa, Spain
J. Zapata Instituto de Química, Facultad de Ciencias Exactas y naturales, Universidad de antioquia, Calle 67 no. 53-108, Medellin, Colombia
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alcohols, terpenols, esters, aldehydes, ketones, acids, ethers, lactones, sulphur and nitrogen compounds, characterize the wine aroma [3, 4]. The presence of these compounds in wines is the result of several factors among which the most important are: grape variety, ripeness, environment, win-emaking process and ageing [2]. Only a small number of aromatic compounds seem to be responsible for the specific aroma of different white wines varieties [5]. among these, the polyfunctional thiols 4-mercapto-4-methyl-2-pentanone (MP), 3-mercaptohexyl acetate (aMH) and 3-mercaptohex-anol (MH) are responsible for box tree, passion fruit, grape-fruit, guava and passion fruit aromas [6–8].
In spite of trace concentrations, thiol molecules play a key role in the aromatic expression of wines. The varietal thiols, identified firstly in Sauvignon Blanc cv. [6], also characterize wines made from various other white Vitis vinifera grape varieties, such as gewürtztraminer, Muscat d’alsace, Colombard, Petit Maseng and botrytized Semillon [9]. The sensory role on the aroma of white wine contrib-uting to fruity, fresh and green notes has been investigated [10]. Several volatile compounds with a thiol function, pre-sent in numerous white wines, have been identified also being responsible for fruity notes in red wines [11].
Other sulphur-containing molecules, such as ben-zenemethanethiol (BM), 2-furfurylthiol (FFT) and 2-methyl-3-furanthiol (MF), are involved in the aromatic profile of various wines; these compounds are responsible for smoky, roasted and empyreumatic aromas in wine [9, 12].
During ageing, the sensory properties of wine alter, due to the change in aromatic composition. In particular, the oxidative degradation of white wine is an undesirable pro-cess where varietal thiols decrease, in the presence of oxy-gen, due to their reactivity with phenolic compounds [13, 14]. as a result, a significant loss of mercaptans occurs, particularly during the first year of ageing; as a result, there is a loss of freshness and tropical fruit notes. In particular, MH and aMH degrade; the former is lost due to oxidation, and the latter hydrolyses to form MH and acetic acid. In fact, aMH has been identified as the least stable thiol in bottled wine [15, 16].
During winemaking and ageing, the presence of antioxi-dant species is responsible for lessening oxidative damage and reducing the loss of volatile thiols. In fact, the thiols content decreases when the amount of antioxidant drops (i.e. free SO2 and reduced glutathione, gSH). The natu-rally occurring tripeptide gSH [17–19] is an effective anti-oxidant. In fact, when added as a wine supplement prior to bottling, it leads to higher MH levels, compared with a con-trol wine, after 6 months of bottle ageing [20].
In addition, it was observed that oxidative damage is reduced during winemaking and wine ageing, due to yeast cell wall antioxidant properties. When yeasts are removed
from the wine, white wines oxidize faster [21, 22]. The employment of well-known winemaking techniques is able to influence the content of sulphur-related odours, i.e. their evolution and disappearance, during the ageing of arneis wine. In this scenario, wines characterized by a different sensory profile could be obtained, leading to a more diver-sified supply in arneis wine production.
In the case of arneis wine, olfactory notes that could be related to thiol compounds were often described, espe-cially in the earlier stage of storage. Moreover, preliminary explorative work analyzed various arneis wines, obtained by different winemaking techniques, and the results showed the presence of varietal thiol molecules (data not shown).
The aim of this work was a preliminary evaluation of the occurrence of aromatic thiol related components, together with more abundant aromatic compounds, in arneis wine during different ageing techniques and in relation to glu-tathione content. Moreover, the sensory significance of such smelling molecules was investigated during ageing. For this purpose, the content of volatile thiols and the over-all volatile composition was evaluated during barrel ageing and in wine stored in stainless steel (ST) tanks. Varying concentrations of reduced glutathione (gSH) were added to bottled wine in order to evaluate their influence on the con-tent of volatile thiols, the overall volatile composition and sensory evolution of the experimental wines.
Materials and methods
Chemicals and reagents
all chemicals, except where otherwise stated, were pur-chased from Sigma (Sigma-aldrich, St. louis, MO, USa), at the highest grade of purity available.
Experimental plan
Influence of ageing technique
Winemaking trials were carried out during the 2010 vin-tage in the “Vaudano Enrico e Figli” winery, located in Cisterna d’asti (asti, Piedmont, Italy). arneis grapes were harvested in crates at maturation (22.0 Brix). a mixture of 30 % ascorbic acid and 70 % SO2, as potassium metabisul-phite (50 mg kg−1), was added directly to the grapes prior to crushing at a concentration of 15 mg Kg−1. The grapes were then crushed, destemmed and pressed; pectic enzyme (1 g hl−1) was then added. The must was immediately cooled to 8 °C and underwent to static decantation. Fer-mentation was started by inoculating 20 g hl−1 of active dry yeast (aDY) (BK1, Tecnofood Italia s.n.c., Santa Maria della Versa, Padova, Italy). Rehydration was carried out in
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warm water for 30 min, as described by the manufacturer. Fermentation took place in ST tanks at 16 °C and lasted 20 days. at the end of aF, SO2 was added to the wine at 30 mg l−1. Subsequently, the following two ageing tech-niques were evaluated: ageing in ST tanks (technique: ST) and barrel ageing (technique: Ba). In the first case, the wine was cooled to 5 °C in order to separate the coarse lees and then transferred into ST tanks. Subsequently, the wine was clarified and underwent the tartaric stabilization pro-cess. Finally, the wine was filtered and bottled after three months of storage.
The wine used for barrel ageing was transferred into a barrel (225 l), with its lees, at the end of fermentation cooled to 5 °C, and the free SO2 was adjusted to 30 mg l−1. The lees were periodically re-suspended; once a week in the first month of ageing and then once every 15 days in the following period of barrel ageing.
Influence of glutathione addition
at the bottling stage (technique ST), the free SO2 was adjusted to 30 mg l−1 and gSH was added to the wines at a concentration of 0, 20 and 40 mg l−1.
analytical methods
Physicochemical analyses
Physicochemical parameters (pH, free and total SO2, total acidity, volatile acidity, reducing sugars, alcoholic percent-age and dry extract) were determined according to official European methods [23]. The total phenolic content of the wine samples was evaluated using Folin-Ciocalteu reactive [24], flavan-3-ols reactive to p-dimethylaminocinnamalde-hyde (DMaCa Index) were determined spectrophotometri-cally according to Di Stefano [25]. analyses were carried out in duplicate except for SO2, which was determined in single repetition using the distillation method [23]. Wine colour was monitored using spectrophotometry (absorb-ance at 420, 520 and 620 nm, on 1 cm of optic pathway), and CIElaB indices (cylindrical coordinates: l* lightness, C* chroma, h* hue) were determined according to Piracci [26].
Overall volatile composition
The analysis was carried out according to gianotti [27] modified as follows: 30 ml of wine was diluted threefold, and 300 µl−1 of 1-heptanol (798 mg l−1) was added as an internal standard; the mixture was extracted using a solid-phase extraction (SPE) method, i.e. loading the sample onto a reversed-phase C18 EC cartridge, 1 g (Biotage, aB Head-quarters Uppsala, Sweden), which was previously activated
with 5 ml of methanol and 5 ml of water obtained from a MilliQ purification system (Millipore, Bedford, Ma, USa). after sample loading, the cartridge was washed with 5 ml of water and the free volatile substances were eluted using 5 ml of dichloromethane. The organic phase, collected in a 25-ml flask, was dried with the addition of anhydrous sodium sulphate, concentrated about 50-fold by evaporation and analyzed using gC–MS.
gC–MS analysis was carried out using an agilent 6890 Series chromatograph equipped with an agilent 5975C mass selective detector (agilent Technologies, Santa Clara, Ca, USa). One μl of concentrate was manually injected into the split–splitless injector, using a Zebron ZB-Wax col-umn (30 m length, 0.25 mm i.d., 0.25-μm film thickness; Phenomenex, Torrance, Ca, USa). Helium was used as the carrier gas, with a constant flow of 1 ml min−1. The injector was kept at 250 °C. The oven temperature was held at 45 °C for 2 min, then raised to 60 °C at a rate of 30 °C min−1, from 60 to 230 °C at a rate of 2 °C min−1, and held at 230 °C for 20 min. The source and transfer line were kept at 230 °C, the quadrupole at 150 °C. The acquisition of mass spectra was carried out in total ion current mode (TIC).
Identification was performed by comparing the mass spectra and retention indices with those of pure standard compounds, while their quantification was carried out by comparison between their peak area and the one corre-sponding to the internal standard peak (1-heptanol).
Volatile thiols analyses
analysis of polyfuntional mercaptans was carried out according to the methodology proposed by Mateo-Vivara-cho et al. [10]. In this method, polyfunctional mercap-tans present in 6 ml of wine are selectively retained in a 50-mg solid-phase extraction cartridge and derivatiza-tion takes place in the same cartridge at room tempera-ture (25 °C) in 20 min by adding small amounts of pen-tafluorobenzyl bromide (PFBBr) and a strong alkali: 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The corre-sponding derivatives are further eluted and determined by gas chromatography–negative ion mass spectrometry (gC–nCI-MS). For quantification, calibration curves were plotted for 2-methyl-3-furanthiol, 2-furfurylthio, 4-methyl-4-mercapto-2-pentanone, 3-mercaptohexyl acetate, 3-mercaptohexanol and benzylmercaptane in wine using 2-phenylethanethiol, 4-methoxy-alpha-toluenethiol and octafluoronaphthalene as internal standards according to Mateo-Vivaracho method [10].
Glutathione analysis
Reduced glutathione was determined by HPlC–fluo-rescence analysis using precolumn online derivatization
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with o-phthalaldehyde (OPa) and 2-aminoethanol (aE) as reported by Park [28]. The HPlC system used (agi-lent 1200 series, agilent Technologies, Santa Clara, Ca, USa) was equipped with an autosampler. Derivatives were separated on a Synergi 4u Hydro-RP 80a column (150 mm × 4.6 mm ID 4 μm, Phenomenex, Torrence, Ca). n-acetylcysteine was added (5 mg l−1) as an internal standard (IS) to wine samples and submitted to precolumn derivatization as follows: 4 μl OPa in methanol was with-drawn (2 mg ml−1), then 5 μl of sample and 4 μl aE (4 mg ml−1 in borate buffer 20 mM pH 8.0) were with-drawn and mixed for 2 min. Separation was performed using a solvent gradient. Solvent a was 50 mM acetate buffer at pH 5.0, and solvent B was 100 % methanol. Deri-vatized glutathione and IS were detected using a fluores-cence detector, where the wavelengths for excitation and emission were 340 and 450 nm, respectively. The ratio between gSH and IS concentrations was compared with the ratio between the corresponding peak areas to obtain the calibration curve. The same wine sample was injected five times under the same analytical conditions in order to assess repeatability for gSH determination, which was characterized by good precision (RSD 6.23 %).
Sensory analysis
The sensory analysis was carried out by a trained panel of the CRa—Centro di Ricerca per l’Enologia comprised of 12 trained tasters, 6 male and 6 female, with an average age of 38 years; all belong to the laboratory staff and have considerable experience in wine sensory analysis. Tasting sessions were performed using ISO (3591–1977)-approved transparent glasses in an ISO (8589–2007) tasting room, for all the tasting sessions. Samples were presented ran-domly and in an anonymous way, using 3-digit random codes. Sensory descriptive analysis was carried out using a nonstructured scale developed at the same institute [29]. This scale consists of an aroma wheel with as many radii (60 mm long) as aroma descriptors, dividing the wheel into equal sectors. all the aroma terms were adapted from the aroma wheel developed by guinard and noble [30]. These aroma terms were identified in previous tastings as the most appropriate to describe the wines. The tasters were asked to choose between more specific descriptors exclud-ing the very generic top level (level 1 in the noble wine aroma wheel). Second level attributes were chosen if more than 50 % of the assessors identified the descriptor, while the third level attributes were chosen if more than 25 % of the assessors identified the descriptor. The sensory profiling was carried out by the same trained panel that had deter-mined the sensory attributes of the wine. For the construc-tion of the ballot, the choice of more specific descriptors was preferred. Judges were asked to mark the perceived
aroma term in the corresponding radius and to score its intensity according to the distance of the mark from the centre of the circle (the longer the distance, the higher the intensity). Each tasting session was repeated twice. Then, distances were measured, and the average of the distances given by all judges was used. Both sensorial and chemi-cal analyses were performed at the end of the aF, after 3 months (corresponding to the bottling for the ST experi-ment), 9 months after the aF and 1 year after the aF.
Statistical analysis
Differences between wines were tested using one-way analysis of variance (anOVa) followed by the post hoc Tukey’s test. The mean values were considered signifi-cantly different when p < 0.05. Correlation coefficients between chemical and sensory variables were measured by Pearson’s correlation coefficient two-tailed test using all the dataset. all the data were submitted to statistical analy-sis using SPSS for Windows ver. 15 (SPSS Inc. Chicago, Il, USa) or by XlSTaT version 2011.2.05 (addinsoft, new York, nY, USa).
Results and discussion
Influence of ageing technique on the wine composition
The amount of naturally occurring glutathione in “Terre alfieri arneis” wine at the end of aF was slightly higher (30.7 mg l−1) than the gSH content measured at crushing (28.40 mg l−1), in agreement with lavigne et al. [18] who showed gSH is released by yeasts during fermentation. Its concentration decreased in the first few months of storage. Surprisingly, after the first 3 months of storage, the high-est amounts of SO2 and gSH were detected in Ba wine, while wines stored in ST tanks showed a lower concen-tration (Table 1). The higher amount of free SO2 in barrel aged (Ba) wine was likely due to its accumulation in the barrel during sanitation practices (méchage) carried out in order to sanitize the barrel before its use [32]. The greater concentration of SO2 in Ba wine can be explained by both the greater concentration of naturally occurring glutathione in barrel and its slower decrease over time; several stud-ies have highlighted the ability of SO2 to prevent gSH oxidation [33]. as expected after 3 months of storage, Ba wines showed a deeper yellow colour measured as absorb-ance at 420 nm and expressed as CIElaB colour space coordinates, in comparison with bottled ST arneis wines (Table 1). This difference is linked to the greater content in phenols and total polyphenols of Ba wines [31].
With regards to the varietal and prefermentative com-pounds at the end of aF (Table 2), arneis wine was
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characterized by a high amount of vinylphenols. among the terpenoids, only linalool was detectable in wine at the end of aF; moreover, its concentration was very low. It is noteworthy that high amounts of cis-3-hexenol were observed in arneis wine, together with a high concentration of other C6 saturated (hexanol) and unsaturated alcohols (data not reported) derived from the oxidative degradation of long unsaturated fatty acids. These compounds can con-tribute to fresh green grass notes perceived in young wines. as regards fermentative compounds, the short and medium fatty acid ethyl esters, related to fresh fruity notes, were high in concentration. Conversely, as expected, diethylsuc-cinate, ethyl lactate and monoethyl succinate were low in concentration at the end of aF; these are high perception threshold compounds and are recognized as related to wine ageing.
The concentration of the acetates of higher alcohols (hexyl acetate, 2-phenylethyl acetate and isoamylacetate) drops quickly in the first month of ageing due to acidic hydrolysis and is independent of the winemaking technique
Table 1 arneis physicochemical composition 3 months after the end of alcoholic fermentation
§ absorbance at 420 nm§§ CIEl*a*b* parameters
Stainless steel (ST) wine
Barrel (Ba) wine
Free SO2 (mg l−1) 16 45
Total SO2 (mg l−1) 100 153
Titratable acidity (g l−1) 4.7 5
Volatile acidity (g l−1) 0.29 0.37
pH 3.18 3.26
Total polyphenols index (mg l−1)
77 114
DMaCa Index (mg l−1) 6.7 14
a 420§ 0.0801 0.1065
l§§ lightness 99.49 97.71
a§§ redness −1.99 −1.88
b§§ yellowness 5.85 6.26
gSH (mg l−1) 21.9 25.1
Table 2 Volatile compounds measured from the end of alcoholic fermentation until 12 months of ageing for control and barrel aged wines
Data reported as mean values ± standard error
BA barrel aged, nd not determined
*, **, *** and n.s. indicate significance at p ≤ 0.05, 0.01, 0.001 and not significant, respectively. all data are in μg l−1 except where indicated
End of aF (n = 3) bottling (n = 3) 9 month (n = 2) 12 month (n = 2)
mean ± se* Control Ba F Sig. Control Ba F Sig. Control Ba F Sig.
Trans oak lactone nd nd 83 – – nd 119 – – – 166 – –
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or SO2 content. These compounds play an important role in the olfactory profile of young wines due to their fresh fruity notes and low perception threshold. after 9 months of stor-age, the overall content of acetates in wines is greater in Ba wines than in the control wine, likely correlated to the greater content of acetic acid [34] and the higher pH of this wine (Table 1). Medium-chain fatty acids and especially C6 alcohols (leaf alcohols) were more stable compounds. Their overall concentration, in particular cis-3-hexenol and hexanol, did not vary significantly during 12 months of ageing; this agrees with several studies that indicate leaf alcohols as very stable compounds and useful as varietal and technological markers [35]. no differences between barrel wines and steel aged wines were noticed relatively to these compounds until 9 months of ageing (Table 2). The rapid formation of diethylsuccinate was observed in both the control wine and Ba wine during storage. The increase in such esters during wine storage is due to chemical esteri-fication of succinic acid by ethanol. Its concentration is strictly correlated to storage conditions (time, temperature, pH) and could be considered a good marker for the degree of wine ageing [36, 37].
Finally, Ba wine was enriched with aromatic molecules extracted from barrel; vanillin, cis and trans oak lactones were identified. Their concentration, as expected, increased during ageing. (Table 2).
With regards to the volatile thiols, their sum in arneis wine was over 400 ng l−1 at the end of aF (Table 3). In particular, MP and aMH were well over above their per-ception threshold. Their OaV (odour activity value) expressed as: concentration/odour threshold was 50 and 4.5, respectively, thus suggesting that all these compounds could contribute to fruity, fresh and green notes of several
wines even at low concentration, as reported by Mateo-Vivaracho et al. [10]. as expected, the thiols concentration decreased rapidly during the first month of ageing, both in the control wine and Ba wines. a difference between these was clearly noticed, even if not statistically significant, as reported in Table 3. Moreover, it is noteworthy that the greatest overall thiols concentration, throughout the stor-age period, was measured in the Ba wine. In this case, the high content in free SO2 could be responsible for the better preservation of thiols and glutathione in wines [13, 38]. In fact, in Ba wine, the free SO2 level was fairly constant dur-ing the ageing period and always greater than the ST aged wines (Table 3). In this case, the protective effect of SO2 was exerted on both volatile thiols and gSH since this latter decreased in accordance with the volatile thiols. Moreover, during barrel ageing, furanthiol derivatives, such as MF and FFT, increased in concentration, as previously reported [39], because the furfural extracted from oak plays a key role in their biogenesis. It is worth highlighting that the only significant statistical differences between these were observed for the FFT and BM concentration at 12 months of storage.
Influence of glutathione addition on wine composition
as previously reported in “Experimental plan” sec-tion, at bottling, the free SO2 in ST wine was adjusted to 30 mg l−1 and three different gSH doses (0, 20 and 40 mg l−1) were added to the wines. Until 9 month of stor-age, no relevant differences were highlighted between these with regards to the fermentation compounds (Table 4). as expected, C6 alcohols did not vary during bottle ageing nor did gSH addition modify their content. Diethylsuccinate
Table 3 Thiols content, SO2 and gSH in experimental wines during bottle and barrel storage
MF 2-methyl-3-furanthio, FFT 2-Furfurilthiol, MP 4-mercapto-4-methyl-2-pentanone, AMH 3-mercaptohexyl acetate, MOH 3-mercaptohex-anol, BM benzylmercaptane, ST stainless steel wine;Ba barrel wine, Pt Perception threshold in ng l−1 all analyses were carried out in duplicate
* These concentrations are FFT units; there is not a calibration curve for this compound
** nd not determined. all data are in ng l−1 except where otherwise stated. The bold font indicates the compounds with an OaV (olfactory activity value) greater than 1
was not affected by the glutathione content in bottled wines, whereas wine pH, temperature and storage time are known to be the most important parameters affecting the formation of this ester in wine. In the case of the acetates of higher alcohols, which play an important role in the olfac-tory characterization of young wines, the acidic hydroly-sis was the driving force responsible for the decline of the content in such esters, regardless of the concentration of reduced glutathione, which is in contrast with some results reported by other authors [40–42]. after 12 months, storage is observed for slight differences in composition, mainly regarding ethyl esters (Table 4).
Wines with added gSH were characterized by a higher content in volatile thiols; moreover, the evaluation of vola-tile thiols showed a statistical significance (effect of gSH addition), only in MP concentration 9 months after bottling (Table 5). In particular, it is noteworthy that in the case of the highest amount of added gSH, the concentration of most volatile thiols 9 months after bottling was near or higher than their perception threshold. These results are in agreement with Ugliano [20] and lavigne [18].
Considering all the data as a whole, it is noteworthy that the amount in volatile thiols was correlated with reduced glutathione content in particular MH, aMH and MF showed a strong positive correlation (Pearson’s coefficient 0.67, 0.85 and 0.76, respectively) with gSH concentration during storage (Table 6). On the contrary, no correlation
was noticed between the thiols content and free SO2. 2-methyl-3-furanthiol, 3-mercaptohexyl acetate, 3-mercap-tohexanol and benzylmercaptane decreased during storage with statistically significant differences between the ninth and twelfth months of storage (Table 6). Only aMH loss during storage followed a different pathway compared with the other compounds; ester hydrolysis is the predominant mechanism leading to the degradation of this volatile thiol. Its fast hydrolysis during the first month of storage, at wine pH, leads to MH and acetic acid accumulation. accord-ingly, a negative correlation (even if not statistically signifi-cant) was observed between MH and aMH.
Changes in the sensory profile of wines
at the end of aF, “Terre Alfieri” Arneis wines were char-acterized by floral, citrus and exotic fruit as well as aca-cia blossom, grapefruit, banana and melon notes (Fig. 1). The attribute “grapefruit” note, which was characterized by a great identification frequency, could be related to the presence of thiol aromatic compounds as reported in previ-ous works [9, 10]. These descriptors, together with colour (straw yellow, greenish highlight) and gustative descrip-tors (sour, structure and bitter), were used for testing wines throughout the entire trial. In the case of Ba wine, two fur-ther descriptors were identified during preliminary sensory analysis: vanilla and honey.
Table 4 Volatile compounds in bottled wines containing different gSH concentration
Different letters along the line (effect of gSH dose) indicate means that are statistically different (p > 95 %). ns not significant. all data are in μg l−1 except where otherwise stated
9 months (n = 2) 12 months (n = 2)
gSH 0 gSH 20 gSH 40 F Sig. gSH 0 gSH 20 gSH 40 F Sig.
The ageing technique affected the aromatic profile. after the first 3 months of ageing, beside citrus, grapefruit and banana notes, Ba wine was characterized by vanilla and honey descriptors corresponding to aromatic compounds released from the barrel (Table 2). Moreover, during the Ba technique, the intensity of vanilla and honey descriptors increased according to the greater content of vanillin and lactones. The intensity of the straw yellow colour increased during ageing, while greenish highlights, grapefruit and floral notes decreased (Fig. 2a). Despite physicochemi-cal analyses highlighting clear differences between Ba and ST wine colour at 3 months of storage, no statistical differences were highlighted during the sensory analyses
concerning their colour (data not shown). Similarly, no statistical differences were measured between Ba and ST wines in their aromatic notes, after 9 months of storage, except for the grapefruit note, which was perceived as more intense in ST wine.
after twelve months of ageing, the straw yellow colour was perceived to be significantly more intense in Ba wine. Moreover, a greenish reflection, grapefruit and acacia notes were perceived as weaker in the Ba wine (Fig. 2b). It is noteworthy that even if a higher content of overall volatile thiols was measured in Ba wines; the sensory descriptors related to their presence were more intense in ST wines; masking effects could be due to the presence of aromatic
Table 5 Volatile thiols in wines during ageing, which contain different gSH
MF 2-methyl-3-furanthiol, FFT 2-furfurylthio, MP 4-mercapto-4-methyl-2-pentanone, AMH 3-mercaptohexyl acetate, MOH 3-mercaptohexanol and BM: benzylmercaptane. nd not determined; all analyses were carried out in duplicate
* These concentrations are reported in FFT units; there is no calibration curve for this compound. all data are in ng l−1 except where other-wise stated. The bold font indicates the compounds with an OaV (olfactory activity value) greater than 1
sum of thiols – 258 374 420 1.0 ns 195 224 236 1.2 ns
gSH (mg l−1) – 2.7 13.6 24 – – 2.1 2.6 4.8 – –
Free SO2 (mg l−1)
– 9 9 11 – – 7 8 8 – –
Table 6 Thiols content in arneis wine during storage
MF 2-methyl-3-furanthiol, FFT 2-Furfurilthiol, MP 4-mercapto-4-methyl-2-pentanone, AMH 3-mercaptohexyl acetate, MOH 3-mercaptohex-anol and BM: benzylmercaptane. all analyses were carried out in duplicate
* These concentrations are reported in FFT units; there is not a calibration curve for this compound
** nd: not determined. all data are in ng l−1 except where otherwise stated. The bold font indicates the compounds with an OaV (olfactory activity value) greater than 1. §pt: Perception threshold
pt§ Months of ageing
3 month 9 month 12 month F Sig.
*MF 1 206a 250a 136b 12.3 0.000
FFT 0.4 0.8 1.3 1.1 0.2 n.s.
MP 0.8 11.7 9.8 9.2 0.5 n.s.
aMH 4.2 21.0a 10.6b 6.1c 60.2 0.000
MOH 60 34.3b 67.5a 51.0ab 8.3 0.03
BM 0.3 1.4b 4.4a 2.7b 5.4 0.015
sum of thiols – 274.3ab 343.3a 206b 10.2 0.01
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compounds strictly related to the barrel ageing technique, such as furans, lactones and aldehydes [43]. Moreover, the grapefruit note perception decreased according to the con-centration of aMH in wine both in Ba wines and ST wines (Table 3).
glutathione addition during bottle storage did not influ-ence the sensory properties of the wine, even during long-term storage. In fact, 6 months after bottling, wines were not different in their straw yellow colour or for greenish reflection attributes. Similarly, the wines were not different in their olfactory description.
nine months after bottling (Fig. 3), a lower colour intensity and higher greenish reflection were measured for the highest gSH trial. acacia blossom as well as banana notes were more intense in the wine containing a lower gSH, while no statistical differences were high-lighted for the grapefruit and melon notes among the tri-als, even if a greater intensity in the +40 gSH trial was measured.
Conclusions
In this work, the volatile composition and sensory profile of DOC Terre Alfieri Arneis wines were investigated. The evolution of these parameters was studied during wine bar-rel and bottle ageing. Moreover, the effect of glutathione content was evaluated during bottle storage.
Varietal thiols were identified, for the first time, in arneis wines (Terre Alfieri Arneis). Despite their low con-centration, these molecules contribute to the fruit and fresh notes in these wines. Their presence plays an important role in the sensory profile of arneis wines as their concentra-tion was found to be above the perception threshold until 12 months of storage. Citrus notes (especially grapefruit notes), together with others, fruity notes decreased rap-idly during the first month of ageing. From a chemical point of view, the decrease in fruity notes corresponded to the reduction in aromatic thiols and acetate esters in both
0
25
50
75
100
FLO
RA
Lac
acia
flow
ers
gera
nium
CIT
RU
Sgr
apef
ruit
lem
onP
OM
Epe
arap
ple
EX
OT
IC F
RU
ITba
nana
mel
onan
anas
DR
UP
ES
peac
hC
AR
AM
EL
hone
yD
RY
VE
GE
TA
Lth
epo
t her
bs
% id
enti
fica
tio
n f
req
uen
cy
Fig. 1 Second level (capital letters, black bars) and third level (grey bars) descriptors identified in arneis wines at the end of aF. Continu-ous line represents the minimum value for second level descriptors, while the dotted line is the threshold for third level attributes
Fig. 2 Effects of ageing technique on sensory profile of arneis wine. a Sensory evalua-tion of arneis wine at 3, 9 and 12 months during Ba. b Sen-sory profile of Ba and ST wine at 12 months of storage. *, ** and *** indicate statistical dif-ferences significant at p ≤ 0.05, 0.01 and 0.001, respectively
Fig. 3 Effect of gSH content on the sensory profile of arneis wines 9 months after bottling
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Ba and ST aged wines. In particular, a high correlation between 3-mercaptohexyl acetate and the grapefruit note was noticed in the wines.
The ageing technique clearly affected the wine composi-tion and sensory profile; Ba wines were both characterized by vanilla and honey notes, and the perception of thiol aro-mas was weaker despite a similar amount being measured in the ST aged wines.
a reduced glutathione concentration in the wine affected volatile thiol loss during barrel and ST ageing. Despite this, at least under our experimental conditions, the addition of gSH at 20 and 40 mg l−1 did not result in any statistically significant differences in sensory results.
Acknowledgments The authors would like to thank the the “Vaudano Enrico e Figli” winery in Cisterna d’asti (asti, Piedmont, Italy) for the kind assistance.
Conflict of interest none.
Compliance with Ethics Requirement This article does not con-tain any studies with human or animal subjects.
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