How do esters and dimethyl sulphide concentrations affect fruity aroma perception of red wine? Demonstration by dynamic sensory profile evaluation

Food Chemistry 194 (2016) 196–200

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How do esters and dimethyl sulphide concentrations affect fruity aroma perception of red wine? Demonstration by dynamic sensory profile evaluation Georgia Lytra, Sophie Tempere, Stéphanie Marchand, Gilles de Revel, Jean-Christophe Barbe ⇑ Univ. Bordeaux, ISVV, EA 4577, Unité de recherche Œnologie, 33882 Villenave d’Ornon, France INRA, ISVV, USC 1366 Œnologie, 33882 Villenave d’Ornon, France

a r t i c l e

i n f o

Article history: Received 4 March 2015 Received in revised form 15 July 2015 Accepted 28 July 2015 Available online 1 August 2015 Keywords: Dimethyl sulphide Esters Fruity aroma Dynamic sensory profiles Aromatic reconstitutions

a b s t r a c t Our study focused on variations in wine aroma perception and molecular composition during tasting over a period of 30 min. In parallel, dynamic analytical and sensory methods were applied to study changes in the wines’ molecular and aromatic evolution. Dynamic sensory profile evaluations clearly confirmed the evolution of the wine’s fruity notes during sensory analysis, highlighting significant differences for red-berry and fresh fruit as well as black berry and jammy fruit, after 5 and 15 min, respectively. Dynamic analytical methods revealed a decrease in ester and dimethyl sulphide (DMS) concentrations in the first few minutes. Sensory profiles of aromatic reconstitutions demonstrated that the aromatic modulation of fruity notes observed during wine tasting was explained by changes in ester and DMS concentrations. These results revealed that variations in concentrations of DMS and esters during wine tasting had a qualitative impact, by modulating fruity aromas in red wine. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction Wine tasters agree that wine aroma evolves in the glass after it is served. This aromatic evolution is probably due to changes in headspace composition over time, as compounds evaporate at varying rates (Hirson, Heymann, & Ebeler, 2012), according to their volatility and affinity for the matrix. Previous research highlighted the role of ethyl esters and acetates in the fruity character of red wines (Falcao, Lytra, Darriet, & Barbe, 2012; Lytra, Tempere, de Revel, & Barbe, 2012a, 2012b, 2014a; Pineau, Barbe, Van Leeuwen, & Dubourdieu, 2009). These studies demonstrated that at least part of the fruity aroma of red wines was due to perceptual interactions between these aromatic compounds, which enhance the perception of fruity aromas, even at concentrations below their individual olfactory thresholds, thanks to synergistic effects (Lytra, Tempere, Le Floch, de Revel, & Barbe, 2013; Pineau et al., 2009). The literature provides evidence that, besides these esters, other compounds that do not necessarily present fruity aromas may have an important impact on the overall fruity aroma of wine. Studies investigating red wine ⇑ Corresponding author at: Univ. Bordeaux, ISVV, EA 4577 Œnologie, F-33140 Villenave d’Ornon, France; INRA, ISVV, USC 1366 Œnologie, F-33140 Villenave d’Ornon, France. E-mail address: [email protected] (J.-C. Barbe). http://dx.doi.org/10.1016/j.foodchem.2015.07.143 0308-8146/Ó 2015 Elsevier Ltd. All rights reserved.

aromas have investigated the impact of dimethyl sulphide (DMS) on fruity aroma expression (Anocibar-Beloqui, Kotseridis, & Bertrand, 1996; de Mora, Knowles, Eschenbruch, & Torrey, 1987; Segurel, Razungles, Riou, Salles, & Baumes, 2004). These studies demonstrated that adding DMS at concentrations above its olfactory threshold conferred blackcurrant and raspberry notes on some young wines, whereas, in older wines, especially those aged in oak barrels, DMS supplementation may produce truffle or hay nuances, and even an unpleasant green-olive odour at excessive concentrations (Anocibar-Beloqui et al., 1996; Segurel et al., 2004). Very recently, Lytra et al. (2014b) used aromatic reconstitutions to demonstrate the sensory importance of DMS, suggesting that it was an active contributor to black berry nuances in the fruity matrix studied. This compound participated, both quantitatively and qualitatively, in modulating black berry fruit aroma and, more specifically, enhancing blackcurrant aroma. The perception of flavour is not a single event but a dynamic process – a series of events – and every step must be considered to obtain a true understanding of flavour (Piggott, 1994). Thus, aroma perception must be matched by dynamic research methods, i.e. including a time component (Dijksterhuis & Piggott, 2001). Sensory profile evaluation is a descriptive approach, widely used to qualify the nature and quantify the intensity of the sensory properties of food (Stone, Sidel, Oliver, Woolsey, & Singleton, 1974). However, in this method, sensory properties are assessed

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immediately after sniffing or eating. Several existing methods take into account the dynamics of perception of a matrix. For example, the time–intensity method was developed by Larson-Powers and Pangborn (1978) to measure the intensity and duration of sweetness, bitterness, sourness, and flavour in solutions. More recently, a descriptive sensory method, known as temporal dominance of sensations (Pineau, Cordelle, Imbert, Rogeaux, & Schlich, 2003), consisted of identifying the dominant sensation and scoring its intensity repeatedly, until the sensation ends. These methodologies usually involve flavour evaluation over a short time period, from a few seconds to a few minutes, once the subject has swallowed the product (Labbe, Schlich, Pineau, Gilbert, & Martin, 2009). These protocols were not applicable to sensory analysis over a 30-min period. The main goal of this work was to evaluate the impact of ester and DMS concentrations evolution on variations in wine fruity aroma during sensory analysis. This required a dynamic process with a series of sensory profiles of a wine over a 30-min period. Then, various aromatic reconstitutions, containing DMS and fruity esters, at concentrations found in the wine itself during the initial tasting, were subjected to sensory analysis, to determine their qualitative contribution to fruity aroma modulation.

2. Materials and methods 2.1. Chemicals and odorant stimuli Absolute ethanol (analytical grade, 99.97%, Scharlau Chemie S.A, Barcelona, Spain) was distilled before use. Sodium sulphate (99%) was also provided by Scharlau Chemie S.A. Microfiltered water was obtained using a Milli-Q Plus water system (resistivity: 18.2 MX cm; Millipore, Saint-Quentin-en-Yvelines, France). Standard-grade compounds were obtained from commercial sources as follows: ethyl propanoate, ethyl 2-methylpropanoate, ethyl butanoate, ethyl hexanoate, ethyl octanoate, ethyl 3-hydroxybutanoate, 2-methylpropyl acetate, butyl acetate, hexyl acetate, DMS, and thiophene from Sigma–Aldrich, Saint-Quentin-Fallavier, France; ethyl-d5 butanoate, ethyl-d5 hexanoate, ethyl-d5 octanoate, and ethyl-d5 decanoate from Cluzeau, Sainte Foy la Grande, France; 3-methylbutyl acetate from VWR-Prolabo, Fontenay-sous-bois, France; and ethyl (2R)-2-hydr oxy-4-methylpentanoate, ethyl (2S)-2-hydroxy-4-methylpentano ate, and ethyl (2S)-2-methylbutanoate were synthesised by Hangzhou Imaginechem Co., Ltd, Hangzhou, China. All compounds used in this work were olfactively pure, as confirmed by the three judges who performed gas chromatography analysis with olfactometric detection of reference compounds. Moreover, a flame ionisation detector analysis confirmed the products’ very high purity.

2.2. Samples 2.2.1. Wine A fruity red wine (Willunga 100 ‘The Tithing’ Grenache, McLaren Vale, Australia, 2010 vintage) that exhibited an interesting evolution of fruity character over time was subjected to instrumental and descriptive sensory analysis.

2.2.2. Aromatic reconstitution To elaborate aromatic reconstitutions (AR), the various compounds were blended together in dearomatised red wine (DRW), at concentrations found in the red wine tasted (Table 1), according to the method described by Lytra et al. (2014b).

Table 1 Ester and DMS concentrations in the aromatic reconstitution. Compounds

Ethyl propanoate Ethyl butanoate Ethyl hexanoate Ethyl octanoate Ethyl 2-methylpropanoate Ethyl 3-methylbutanoate Ethyl (2S)-2-methylbutanoate Ethyl (2R)-2-hydroxy-4methylpentanoate Ethyl (2S)-2-hydroxy-4methylpentanoate Ethyl 3-hydroxybutanoate Butyl acetate Hexyl acetate 2-Methylpropyl acetate 3-Methylbutyl acetate Dimethyl sulphide (DMS)

Concentrations (lg/L) t = 0 min

t = 5 min

t = 15 min

321 335 477 440 245 98 55 190

268 257 436 400 204 85 41 182

259 236 395 358 184 72 36 174

10

9

8

300 10 5 46 460 44

270 9 4 38 342 35

250 8 4 33 312 26

2.3. Analytical methods 2.3.1. Experimental procedure Prior to the first sensory tests, the kinetics of variations in the concentrations of the compounds listed in Table 1 was evaluated during wine tasting, in order to assess the evolution of the composition of the wine submitted to the panel. The wine was prepared under the same conditions used during sensory analysis. It was poured into seven ISO glasses (ISO 3591, 1977) and then swirled twice every 5 min. After swirling, one glass was collected to analyse its contents (using the analytical methods described in Sections 2.3.2. and 2.3.3), thus obtaining samples at t = 0, t = 5 min, t = 10 min, t = 15 min, t = 20 min, t = 25 min, t = 30 min. 2.3.2. DMS analysis Chromatographic conditions and sample preparation were as described by Lytra et al. (2014b), inspired by Anocibar-Beloqui et al. (1996). A 100-mL sample was placed in a 125-mL vial at room temperature and 10 lL of the internal standard (thiophene 330 mg/L) were added. The vial was then sealed using a screw-top cap with a Teflon-faced septum. After 24 h at 22 °C and away from direct light, 1 mL of gaseous phase was injected using the headspace technique (HS). DMS was assayed by injection into an HP-5890 gas chromatograph coupled to a flame photometric detector (injector temperature: 70 °C, interface temperature: 150 °C), using an HP5 column. The oven was programmed at 30 °C for the first minute, raised to 100 °C at 10 °C/min, and, finally, increased at 20 °C/min to a final isotherm at 180 °C. The carrier gas was hydrogen 5.5 (Air Liquide, France). 2.3.3. Ester analysis Chromatographic conditions and sample preparation were as optimised by Antalick, Perello, and de Revel (2010), using solid-phase microextraction (SPME). The fibre (Supelco, Bellefonte, PA) was coated with 100 lm polydimethylsiloxane stationary phase (PDMS-100). For the quantitative study, 20 lL of a stock solution of internal standards, ethyl-d5 butanoate, ethyl-d5 hexanoate, ethyl-d5 octanoate, and ethyl-d5 cinnamate at about 200 mg/L each in absolute ethanol, was added to 25 mL of the samples. A 10-mL sample of the mixture was placed in a 20-mL headspace vial, 3.5 g sodium chloride were added, and the vial was tightly sealed with a PTFE-lined cap. The solution was homogenised in a vortex shaker and then loaded onto a Gerstel (Mülheim an der Ruhr, Germany) autosampling device. Gas chromatography analyses were carried out on an HP 5890 GC system

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coupled to an HP 5972 quadrupole mass spectrometer. Injections were in splitless mode (injector temperature, 250 °C; interface temperature, 280 °C) and a BP21 capillary column (50 m  0.32 mm, film thickness, 0.25 lm; SGE, Ringwood, Australia). The oven temperature was programmed at 40 °C for 5 min, then raised to 220 °C at 3 °C/min, and held at that temperature for 30 min. The mass spectrometer was operated in electron ionisation mode at 70 eV in selected-ion-monitoring (SIM) mode. 2.4. Sensory analysis 2.4.1. General conditions A panel of 10 judges, 3 males and 7 females, aged 29 ± 8 (mean ± SD) volunteered for sensory analysis. All panellists were research laboratory staff at ISVV, Bordeaux University, selected for their experience in assessing aromas in red wines. Sensory analyses were performed as described by Martin and de Revel (1999). Samples were evaluated at controlled room temperature (20 °C), in individual booths, using covered, black, ISO glasses (ISO 3591, 1977) containing about 50 mL liquid. 2.4.2. Sensory analysis of wine over a 30-min period A glass of the red wine studied was presented to each member of the panel. During the descriptive wine analysis, judges were asked to choose free descriptors at 5-min intervals over a period of 30 min. The glass was swirled twice before olfaction (t = 0 min-before agitation, t = 0 min-after agitation, t = 5 min, t = 10 min, t = 15 min, t = 20 min, t = 25 min, t = 30 min) and the terms cited were selected to obtain characteristic descriptors for the whole panel. A glass of the red wine studied was once again presented to each member of the panel. Dynamic sensory profiles in wine were then evaluated for red and black berry fruit, fresh and jammy fruit, vegetal, spicy, and smoky/toasted aroma intensity. The subjects swirled the glass twice every 5 min, before olfaction, then rated the intensity of these descriptors (t = 0 min-before agitation, t = 0 min-after agitation, t = 5 min, t = 10 min, t = 15 min, t = 20 min, t = 25 min, t = 30 min) on a 100-mm unstructured scale ranging from ‘‘no odour perceived’’ on the left to ‘‘very intense’’ on the right (Martin & de Revel, 1999).

3. Results 3.1. Evolution of wine composition during sensory analysis Prior to the sensory tests, the evolution kinetics of the compounds in the wine submitted to the panel was evaluated, to assess variations in ester and DMS concentrations. This kinetic evaluation demonstrated that concentrations of the esters and DMS in wine decreased in the first few minutes (Fig. 1). After 10 min, the concentrations of certain compounds in wine had decreased by up to 50%, and up to 70% after 30 min. 3.2. Evolution of the intensity of fruity notes in wine during sensory analysis Descriptive analysis of the wine by the 10-member panel revealed that the descriptors most frequently cited were red and black berry fruit, fresh and jammy fruit, vegetal, spicy, and smoky/ toasted. After these initial observations, the wine was presented to the panel again and dynamic sensory profiles for these descriptors were evaluated over a 30-min period, as described in Section 2.4.1. The dynamic sensory profiles in wine revealed significant differences for red berry fruit, black berry fruit, fresh fruit and jammy fruit (Fig. 2). Red berry and fresh fruit aroma intensity had increased significantly at 5 min, while the intensity of black berry and jammy fruit aroma was significantly higher at 15 min. In contrast, the average scores for vegetal, spicy, and smoky/toasted aroma intensity remained identical throughout sensory analysis (results not shown). 3.3. Role of DMS and esters in the evolution of fruity notes during sensory analysis As shown in Fig. 3, when DRW was supplemented with the concentrations of esters and DMS found in the wine during sensory analysis after 5 min, the average intensities for red berry and fresh fruit aromas were significantly higher, while the average intensities for black berry and jammy-fruit aromas were significantly higher when DRW was supplemented with the concentrations of esters and DMS found in the wine during sensory analysis after 15 min. 4. Discussion

2.4.3. Sensory analysis of aromatic reconstitutions Aromatic reconstitutions were prepared in DRW using 13 esters (Lytra et al., 2014b) and DMS at concentrations found in the wine evaluated, at time 0, 5, and 15 min during the sensory analysis (Table 1). Three glasses containing the aromatic reconstitutions were presented to each member of the panel. The sensory profiles of these three aromatic reconstitutions were evaluated for red-and black berry fruit, and fresh and jammy fruit aroma intensity on a 100-mm scale. Sensory analyses of the wine and aromatic reconstitutions were duplicated in order to validate the sensory modifications observed. 2.4.4. Statistical data analysis Statistical data were analysed using the Kruskal–Wallis (Steel– Dwass–Critchlow–Fligner) statistical non-parametric test (XLSTAT software). All descriptors are mean-centred per panellist and scaled to unit variance. The statistically significant level was 5% (p < 0.05). The findings of the sensory analyses for both the wine and the aromatic reconstitutions were confirmed by repeat experiments (each session was conducted in duplicate). The results shown represent the addition of mean-centred values for each panellist and descriptor in both sessions.

The main goal of this work was to examine aromatic and molecular evolution in parallel, using dynamic analytical and sensory methods. The impact of ester and DMS concentrations in the headspace on variations in wine fruity aromas was evaluated during sensory analysis, a dynamic process over a 30-min period. In particular, this work aims to understand how the molecular composition of wine may change sensory properties over time under real wine tasting conditions, as described by Hirson et al. (2012). The kinetics of variations during a 30-min sensory analysis session revealed a decrease in concentrations of esters and DMS in the first few minutes. This finding supports the hypothesis that a wine’s aromatic evolution under these conditions is due to physicochemical phenomena: headspace composition changes over time as some compounds evaporate, according to their volatility and affinity for the matrix, due to interactions involving, for example, Van der Waals forces or hydrogen bonds between aromatic compounds and nonvolatile constituents of the matrix (Saenz-Navajas et al., 2010). The nonvolatile components of the matrix are apparently able to modulate headspace composition, thus impacting the aromatic perception of the wine (Lorrain et al., 2013; Saenz-Navajas et al., 2010). Dynamic sensory profiles clearly confirmed the evolution of the intensity of the wine’s fruity notes over a 30-min period, revealing

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0

5

10

15

20

25

30

decrease in concentraon (%)

0 -10 -20 -30 DMS

-40 -50 -60 -70 -80 Time (min) 0

5

10

15

20

25

30

decrease in concentraon (%)

0

C3C2

-10

iC4C2

-20

C2iC4

-30

C4C2

-40

2-mC4C2 iC5C2

-50

C2iC5

-60

C6C2

-70

C2C6

-80

C8C2 Time (min)

Fig. 1. Evolution of ester and DMS concentrations in wine during a 30-min sensory analysis session.

1,5

t = 0 min (b.a) t = 0 min t = 5 min t = 10 mint = 15 mint = 20 min t = 25 mint = 30 min

1,5

t = 0 min (b.a) t = 0 min t = 5 min t = 10 min t = 15 min t = 20 min t = 25 mint = 30 min

Mean-centered intensity values

Red-berry fruit

Black-berry fruit

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1

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t = 0 min (b.a) t = 0 min t = 5 min t = 10 mint = 15 mint = 20 min t = 25 mint = 30 min

-1,5

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ab

ab

b

a

Jammy fruit 1

0,5

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-1,5

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t = 0 min (b.a) t = 0 min t = 5 min t = 10 min t = 15 min t = 20 min t = 25 mint = 30 min

Fresh fruit 1

-1

a

-1

bcd

cd

d

bcd

bc

ab

ab

a

-1,5

a

a

ab

bc

c

bc

abc

abc

Fig. 2. Evolution of the intensity of fruity notes in wine during a 30-min sensory analysis session. Mean-centred values with different letters are significantly different (p < 0.05). b.a; before agitation. Error bars indicate the 95% confidence interval on the mean value.

significant differences for red berry and fresh fruit, as well as black berry and jammy fruit at 5 and 15 min, respectively. Sensory profiles of aromatic reconstitutions in DRW demonstrated that ester and DMS levels evolution explains aromatic

unfolding for red berry, black berry, fresh fruit and jammy fruit notes during sensory analysis. Supplementing the DRW with esters and DMS at the concentrations found in the wine during wine tasting produced the same olfactory modifications in the fruity notes

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Mean-centered intensity values

1,5

t = 0 min

t = 5 min

t = 15 min

Red-berry fruit

1,5

t = 0 min

t = 5 min

t = 15 min

Black-berry fruit

1,5

t = 0 min

t = 5 min

t = 15 min

Fresh fruit

1,5

1

1

1

1

0,5

0,5

0,5

0,5

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-1

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-1,5

t = 5 min

t = 15 min

Jammy fruit

-1

a -1,5

t = 0 min

b

a

a

ba

-1,5

Fig. 3. Mean-centred intensities of descriptors for aromatic reconstitutions made from dearomatised red wine supplemented with different concentrations of esters and DMS. Mean-centred values with different letters are significantly different (p < 0.05). Error bars indicate the 95% confidence interval on the mean value.

over time. More precisely, adding esters and DMS at the concentrations found in wine after 5 min evolution to the matrix resulted in the same olfactory modifications in red berry and fresh fruit notes reported in wine during sensory analysis. Also, adding esters and DMS at concentrations found in wine after 15 min evolution resulted in the same olfactory modifications of black berry and jammy fruit notes reported in wine during sensory analysis. This work also revealed the indirect qualitative impact of DMS on fruity aroma expression. Although it does not possess any fruity aromas, it contributed actively to fruity aroma perception. Lytra et al. (2014b) revealed the indirect qualitative impact of DMS on fruity aroma expression. Black berry fruit and, specifically, blackcurrant aroma intensity in the aromatic reconstitution was significantly higher in dearomatised red wine supplemented with 20 lg/L DMS, confirming the contribution of DMS to the blackcurrant nuances in this matrix. These DMS levels were relatively close to those found during this experiment after 15 min in the glass (26 lg/L), thus highlighting the role of DMS as a natural enhancer of black berry fruit aroma. These results also highlight the considerable impact of esters and DMS on the molecular composition of wine aroma and, particularly, the complexification and intensification of fruity wine aroma, perceptible during sensory analysis. Aroma release and perception is a dynamic process that must be studied using dynamic methods. Dynamic sensory methods are gaining increasing application, in parallel with the development of dynamic chemical methods for studying the process of flavour release from foods (Piggott, 2000). These methods have enhanced our understanding of food flavour and, to a limited extent, flavour release can be predicted on the basis of the physical chemistry of the flavour compounds and the corresponding matrix. These experiments clarified current knowledge of changes in both the molecular composition and fruity notes of a wine, detected during wine tasting, using dynamic analytical and sensory methods. Taken together, these data revealed the evolution of a wine’s fruity notes during tasting, as well as a decrease in ester and dimethyl sulphide concentrations. However, further work is required to improve dynamic sensory process methodologies and collect sufficient physicochemical data to predict aroma release from complex matrices such as wine. Acknowledgements The authors thank Liberty Wines Ltd (London) for providing wine samples. References Anocibar-Beloqui, A., Kotseridis, Y., & Bertrand, A. (1996). Détermination de la teneur en sulfure de diméthyle dans quelques vins rouges. Journal International des Sciences de la Vigne et du Vin, 30, 167–170.

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