Accepted Manuscript
Characterisation of Australian Verdelho wines from the Queensland GraniteBelt region
Francesca Sonni, Evan G. Moore, Fabio Chinnici, Claudio Riponi, Heather E.Smyth
PII: S0308-8146(15)30057-1DOI: http://dx.doi.org/10.1016/j.foodchem.2015.10.057Reference: FOCH 18252
To appear in: Food Chemistry
Received Date: 20 May 2015Revised Date: 2 September 2015Accepted Date: 12 October 2015
Please cite this article as: Sonni, F., Moore, E.G., Chinnici, F., Riponi, C., Smyth, H.E., Characterisation ofAustralian Verdelho wines from the Queensland Granite Belt region, Food Chemistry (2015), doi: http://dx.doi.org/10.1016/j.foodchem.2015.10.057
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Characterisation of Australian Verdelho wines from the Queensland Granite Belt region
Francesca Sonnia,b,*
, Evan G. Moorec, Fabio Chinnici
a, Claudio Riponi
a, Heather E. Smyth
b
aDepartment of Agricultural and Food Science, Alma Mater Studiorum, University of Bologna, Viale
Fanin 40, 40127 Bologna, Italy.
bCentre for Nutrition and Food Science, Queensland Alliance for Agricultural and Food Innovation,
University of Queensland, QLD, 4072, Australia
cSchool of Chemistry and Molecular Biosciences, University of Queensland, QLD, 4072, Australia.
*Corresponding author. Tel.: +61 733 651 854; fax: +61 733 460 539. E-mail address:
Abstract
Verdelho is a white-grape-vine, growing well in the Granite Belt region of Queensland. Despite its
traditional use in Madeira wine production, there is scant literature on the flavour characteristics of this
variety as a dry wine. In this work, for the first time, volatile compounds of Verdelho wines from the
Granite Belt have been isolated by solid phase extraction (SPE), and analysed using gas chromatography-
mass spectrometry (GC-MS). A corresponding sensory characterisation of this distinctive wine style has
also been investigated, using sensory descriptive analysis. Chemical compounds that mostly contribute to
the flavour of these wines were related to fruity sweet notes (ethyl esters and acetates), grassy notes (3-
hexenol), floral aromas (2-phenylethanol and β-linalool) and cheesy aromas (fatty acids). Sensory
analysis confirmed that the Verdelho wines were characterised by fruity aroma attributes, especially
“tree-fruit” and “rockmelon”, together with “herbaceous”, while significant differences in the other
attributes were found.
Keywords: Verdelho wine, volatile compounds, GC-MS, sensory descriptive analysis
1. Introduction
Wine is a highly complex beverage matrix, with an aroma profile consisting of several hundred
compounds, representing a variety of different chemical classes, with a wide range of boiling points,
differing aroma potencies and present in concentrations from the mg/l to the ng/l range (Ebeler, 2001).
Historically, analytical investigations in flavour chemistry were performed assuming that all volatiles
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contribute to the aroma, and consequently analytical procedures, such as gas chromatography, were
confined to identifying and quantifying volatiles and elucidating the sensory relevance of these
compounds (Grosch, 2001). The compounds that were easily accessible from an analytical point of view
were compounds present at relatively high concentration. However, more recently, advances in analytical
instrumentation together with improved isolation and pre-concentration steps involved in sample
preparation techniques have made possible the analysis of compounds present in much lower
concentrations, leading to an improved understanding of the types of compounds present (Lopez, Aznar,
Cacho, & Ferreira, 2002). At the same time, although hundreds of different volatile compounds may be
present in a given wine, it has been recognised that only a subset of these are likely to be actively
contributing to aroma (Grosch, 2000). In order to truly understand the olfactory impact of identified
volatiles and their real sensory contribution, it is therefore necessary to explore the relationships between
volatile composition and sensory properties (Francis & Newton, 2005) and to validate relationships
between compounds and sensory attributes using reconstitution, spiking and omission models (Grosch,
2001). To this end, quantitative descriptive analysis is one of the most comprehensive and informative
tools used in sensory analysis, and it has been successfully used for characterising the aromatic profile of
many wine varieties by several authors (Campo, Ballester, Langlois, Dacremont, & Valentin, 2010; Tao,
Liu, & Li, 2009; Parr, Green, White, & Sherlock, 2007; Sánchez-Palomo, Díaz-Maroto Hidalgo,
González-Viñas, & Pérez-Coello, 2005; Smyth, Cozzolino, Herderich, Sefton, & Francis, 2005).
Chemical analysis together with sensory investigation allows the characterisation of a product that
expresses typical flavour characteristics, as a function of its physical and cultural environment (Parr et al.,
2007; Maitre, Symoneaux, Jourjon, & Mehinagic, 2010).
Verdelho is a grape cultivar characterized by its thick skin, and it has been traditionally used since the
15th century as one of the five main grape varieties for the production of fortified wines in Portugal and
the islands of Madeira off the coast of Morocco in North Africa (Perestrelo, Albuquerque, Rocha, &
Câmara, 2011). In Australia, where the first plantings of cv Verdelho were made in the 1820s, this variety
has been successfully grown especially in the warm-climate wine regions of Southern Queensland (South
Burnett and Granite Belt), where it is used for the production of dry white wines. In particular, the
Granite Belt, which takes its name from the igneous rock deposits in the area, is typified by its cold
winter months, due to its elevation that ranges from 450 m to 900 m above sea level. This, together with a
relatively low rainfall, yields climatic conditions that are suitable for producing high quality wines from
vines well suited to the environment. In this region, Verdelho wines make up almost 25% of the entire
Queensland production, making this grape of particular importance for the Queensland Wine Industry
(Wine Australia, 2012). Furthermore, with Verdelho listed as one of the top 10 premium white wine
grape varieties nationally (Gordon 2005), the future demand for Verdelho can be expected to rise.
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Despite the increasing production and consumer interest in this wine variety, there remains a distinct lack
of scientific literature concerning its chemical and sensory characteristics. In this study, we present the
first ever complete volatile profile characterisation for several of the most representative commercial
Australian Verdelho wines from the Granite Belt region, in order to characterise the aroma profile of this
variety and identify some potential quality markers for this cultivar, as a function of the specific
production area. To achieve this aim, solid-phase extraction (SPE) and gas chromatography with mass
spectrometric (GC-MS) detection were utilised, resulting in the quantification of a wide range of volatile
compounds that potentially contribute to the unique wine aroma. For a more complete characterisation of
the Verdelho variety aroma profile, free and bound monoterpenes have also been analysed. At the same
time, these wines have been subjected to quantitative descriptive sensory analysis, both to compare the
sensory evaluation of the different products and also with the aim of highlighting specific characteristics
that typify this wine variety and geographical production area.
2. Material and methods
2.1. Wine samples
In this study, eight commercial Australian wines from cv. Verdelho (2012 vintage), originating from the
Queensland Granite Belt region, were analysed. Each of the wines selected have been subjected to as near
as possible identical commercial winemaking protocols, consisting of soft pressing of grapes, cold
clarification, alcoholic fermentation and ageing in stainless steel tanks for six months before being
bottled. Samples were identified using labels from VD1 to VD8.
2.2. Reagents and standards
Standard reference compounds for GC-MS analysis were supplied by Sigma Chemicals (St. Louis,
Missouri, USA), Fluka Chimie AG (Buchs, Switzerland), and Alfa Aesar (Karlsruhe, Germany).
Dichloromethane and methanol (SupraSolv) were supplied by Merck (Darmstadt, Germany), absolute
ethanol (ACS grade) was obtained from Scharlau Chemie (Sentmenat, Spain), and pure water was
obtained from a Milli-Q purification system (Millipore, USA). LiChrolut EN resin for solid-phase
extraction (SPE) prepacked in 200 mg cartridges (3 ml total volume) were purchased from Merck
(Darmstadt, Germany).
2.3. Oenological parameters
Sample pH was determined by automatic titration with a 702 SM Titrino apparatus (Metrohm, Herisau,
Switzerland). Free and total SO2 were measured with a colorimetric method based on a chemical reaction
with a chromogen in the visible range (R-Biopharm AG, Darmstadt, Germany). The alcohol content of
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wines was determined by a UV-method using an enzymatic test-kit (R-Biopharm AG, Darmstadt,
Germany). Sample colour was determined by direct measurement at 420 nm (after filtration at 0.45 nm
with PTFE filters) using a DU 530 UV/Vis spectrophotometer (Beckman Coulter, Brea, California,
USA). Quantification of malic and lactic acids was conducted following the HPLC procedure described
by Castellari et al. (2000). The HPLC utilised was a Shimadzu apparatus (Shimadzu Corporation, Tokyo,
Japan) equipped with a cooling autosampler (SIL-20AC), a system controller (SCL-10A), an isocratic
pump (LC-10AT), a column oven (CTO 10A), and a photodiode array detector (SPD-M10A). The
column was a Bio-Rad Aminex HPX-87H (300 mm × 7.8 mm) for analysis of organic acids, the injection
volume was 20 µl and the UV detector was set at a wavelength of 210 nm. At the time of analysis, the
wines were 8 months old.
2.4. Extraction of free and bound volatile compounds
For the analysis of volatiles, in order to provide a rapid and solventless technique for concentration and
isolation of analytes from the sample matrix, a solid-phase extraction (SPE) with a polymeric sorbent was
used. The SPE extraction method was a modification of a developed and validated method outlined by
Lopez et al (2002), using a 20 ml wine sample (containing 100 µl of 2-octanol at 514 mg/l as an internal
standard). Analytes were recovered by elution with 5 ml of dichloromethane, and concentrated to a final
volume of 200 µl under a stream of pure nitrogen (N2), prior to GC-MS analysis. Analyses were
performed in duplicate and mean values were used in further data processing.
For the analysis of the bound volatile compounds, wine samples were first treated with a commercial
enzyme preparation based on pectinase and β-glucosidase (2000 β -D-Glu u/g) derived from Aspergillus
niger (OenoBioTech, Chanteloup en Brie, France) in order to hydrolyse the fraction of terpenes bonded
with glucose as monoglucosides and diglycosides in the wine. Hence, 20 ml of wine sample (containing
100 µl of 2-octanol at 514 mg/l as an internal standard) was added to 20 ml of citrate phosphate buffer
(pH 5.4) in order to dilute the alcohol and sugar contents, and to increase the wine pH, in order to
guarantee the highest enzyme activity. Samples were then treated with the enzyme preparation in excess
(2.6 ml of a 250 g/l solution of the enzyme in water), and stored at 38°C for 18 hours. Subsequently,
samples were subjected to the same SPE extraction method applied to the other wine samples, and
analysed by GC-MS. The amount of volatile compounds obtained after enzymatic treatment represent the
total fraction, which can subsequently be used to estimate the quantity of bound volatile compounds, as a
difference between the total and free fractions.
2.5. GC/MS analysis
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Samples were analysed with an Agilent 6890N gas chromatograph (GC) equipped with a 5975 mass
spectrometric detector (MSD) (Agilent Technologies, Palo Alto, CA, USA). The GC was fitted with a
DB-WAX column (J&W Science, i.d. = 0.25 µm, length = 30.0 m, film thickness = 0.25 µm) and helium
(BOC gases, ultrahigh purity) was used as a carrier gas at a flow rate (constant flow) of 1.0 ml/min. A
programmed temperature vaporiser (PTV) injector (Gerstel, Mülheim an der Ruhr, Germany) was used,
with an unpacked glass liner (Supelco, St Louis, MO, USA, i.d. = 2 mm).
The GC oven temperature started at 45 °C for 1 min, was heated at 3 °C/min to 100°C, and then heated at
5 °C/min to 240°C (held for 10 min). The injection temperature was 250°C. The wine sample extracts
were injected with a 10 µl liquid injection syringe using an automated Multi Purpose Sampler (MPS2)
(Gerstel, Mülheim an der Ruhr, Germany). The injection volume was 1 µl at a speed of 50 µl/sec in
splitless mode.
The MSD ion source was maintained at 250°C. Analyte detection was carried out by positive ion electron
ionization (EI) mass spectrometry in selected ion monitoring mode (SIM) for terpene compounds and in
the full scan mode for all other volatile compounds, using an ionisation energy of 70 eV and a transfer
line temperature of 220°C. The characteristic ions selected (m/z) for each target volatile terpene in SIM
mode were (the m/z ratios used for quantification are shown in parentheses): cis/trans-linalool oxide (59),
94, 137; β-linalool (71), 93, 121; isopulegol (67), 81, 121; α-terpineol (93), 121, 136; β-citronellol (69),
95, 123; geraniol (69), 93, 123; nerol (69), 93, 121. Utilising SIM mode ensured that several terpenes
could be identified and quantified even if they were present at very low levels in the samples. For the
other compounds, the mass acquisition range used was from m/z 33 - 400 and the scanning rate was 1
scan/sec.
Data analysis was carried out with MSD ChemStation Data Analysis software (Agilent Technologies).
Chromatographic peaks were identified by comparing their mass spectra and retention times with those of
authentic standards and/or those reported in the literature or in commercial libraries NIST 2.0 and Wiley
7 (P > 90%). Of the 56 total compounds found in our samples, 43 were identified using reference
standards, and 13 using commercial libraries and information reported in literature.
Semi-quantification of terpenes in SIM mode was carried out using the selected ion (m/z) of the 2-octanol
(45) internal standard. Semi-quantification of the other compounds in full scan mode was carried out via
the total ion current peak areas according to the internal standard method.
Calibration curves were obtained by duplicate injection of five standard solutions containing a mixture of
74 commercial standard compounds at two different ranges of concentration: 0, 0.5, 5, 50, 500 µg/l, and
0, 5, 50, 500, 5000 µg/l, according to their usual concentrations found in wine, with a constant
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concentration of the internal standard 2-octanol (2.57 mg/l). The calibration equations for each compound
were obtained by plotting the peak area response ratio (target compound/internal standard) versus the
corresponding concentration ratio (target compound/internal standard).
Linearity was found throughout the range for each component, with r-values between 0.9281 and 0.9998.
For compounds lacking reference standards, the calibration curves of standards with similar chemical
structure were used.
2.6. Odour activity values
To evaluate the contribution of a chemical compound to the aroma of a wine, the odour activity value
(OAV) was determined. OAV, also called aroma or odour units, or aroma values, is a useful measure to
assess the relative importance of a specific compound to the odour of a sample. The odour activity value
was calculated as the ratio between the concentration of an individual compound and the perception
threshold (OTH) found in the literature (Tufariello, Capone, & Siciliano, 2012; Vilanova, Genisheva,
Masa, & Oliveira, 2010; Gómez-Míguez, Cacho, Ferreira, Vicario, & Heredia, 2007; Culleré, Escudero,
Cacho, & Ferreira, 2004) and ideally determined in a similar matrix (e.g. model wine).
2.7. Sensory analysis
After a preliminary screening session, five of the eight Verdelho wines analysed in this study were further
evaluated using descriptive sensory techniques, together with four Australian Viognier wines (results for
which will be reported elsewhere). The sensory panel consisted of 13 assessors, 6 women and 7 men
(aged from 28 to 58) who had been previously tested for sensory acuity, were experienced in sensory
analysis, and were recruited from staff and students of the Health and Food Sciences Precinct, Coopers
Plains, Qld. As per the sensory descriptive analysis method, the assessors were trained using freshly
opened bottles of the Verdelho wine samples during nine sessions. The panellists were asked to assess
samples for appearance, aroma, flavour, mouthfeel and aftertaste, and generate a list of sensory terms.
Standardized wine aroma terminology proposed by Noble (2003) and Gawel, Oberholster, & Francis
(2000) were presented during initial training sessions to assist with vocabulary development. A total of
twenty-two (22) attributes were selected by consensus to describe the wine samples, including three for
the appearance, eleven for the aroma, and eight for the mouthfeel/palate. Over the course of the training
sessions, a verbal definition was developed for each sensory attribute, together with aroma reference
standards that were presented, discussed and agreed upon by the panel. Table 1 summarises all of the
sensory attributes together with verbal definitions and the composition of the sensory reference standards.
The final training session was a practice booth session whereby samples of wines were presented to the
panel in individual booths, under controlled lighting and temperature, together with filtered water for
7
palate cleansing and reference standards and definitions. Panellists were asked to assess the standards,
then assess and rate the wines for each of the attributes using the scales on the computer. Data was
collected using the Compusense five software (version 5.0.49, Guleph, Canada). The purpose of the
practice session was to ensure the attributes, definitions and scales selected were relevant, to assess
panellist performance, and to familiarise the panel with the set-up of the formal evaluation sessions. Nine
formal evaluation sessions were undertaken to evaluate the intensity of the twenty-two attributes for each
of the wines selected using an unstructured line scale anchored from “low/none” to “high”. In each
session, a total of 4 random wine samples (30 ml at 22°C) were presented on white trays according to a
balanced Latin square block design in coded wines glasses (ISO 3591). Each of the wines were poured
immediately prior to each session, samples were served covered with a lid (watch glass) and each wine
was evaluated by each panellist in triplicate.
2.8. Statistical analysis
Statistical analysis of GC-MS data and sensory data was performed using the XLSTAT Software package
(Version 2013.2, France). For each wine, significant differences in mean concentrations of volatile
compounds and in sensory attributes were tested by one-way analysis of variance (ANOVA) followed by
a post hoc comparison (Tukey’s test at p < 0.01 for the volatile compounds, and at p < 0.05 for the
sensory attributes). Pearson’s correlation was analysed for all the volatiles found in the samples, in order
to underline which compounds were correlated with each other (r ≤ -0.85; r ≥ 0.85).
3. Results and discussion
3.1. Oenological parameters (General composition of wines)
Eight commercial Australian wines from cv. Verdelho (2012 vintage), all originating from the Granite
Belt region, were selected for preliminary screening and subjected to a basic chemical characterisation,
with resulting data as shown in Table 2. The wines were without obvious defects, such as oxidative or
reductive aromas. The pH, alcohol content, free and total SO2, and organic acid content were used for
basic characterisation of the wines, as important parameters directly correlated with the wine quality and
stability. The Verdelho samples showed a broad range of pH (from 2.85 to 3.34) and differing alcohol
content (from 12.0% to 13.7%), which has been shown to have an impact on the perception of certain
aroma notes in wines (Fisher, Berger, Hakansson, & Noble 1996; Guth & Sies, 2001). It has previously
been noted that decreasing alcohol content in a reconstituted wine model increases the sensory perception
of ‘fruity’ and ‘flowery’ notes as well as increasing the perception of in-mouth acidity (Guth & Sies,
2001).
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The free and total SO2 values were found to range from 83.6 to 231 mg/l (total) and 4.77 to 30.2 mg/l
(free), while the optical density (O.D.) at 420 nm values ranged from 0.027 to 0.056 with the highest level
obtained for VD6.
In terms of their overall organic acid content, the levels of malic acid and lactic acid in these samples
(obtained by HPLC analysis) did not demonstrate any large differences between the various wines (with a
range from 1.25 g/l to 2.39 g/l for the malic acid and from 0.32 g/l to 0.56 g/l for the lactic acid).
Observed differences may be attributed to the diverse composition of the initial must used in the wines
elaboration that may be due to climatic variations.
3.2. Volatile characterisation of wines
3.2.1. General
Overall, fifty-six volatile aroma compounds were identified and quantified for the 8 Verdelho wines, and
the results were subjected to ANOVA (p<0.01), with the aim of highlighting significant differences
between volatile compounds present in the wine samples. As expected, the volatile chemical data ranged
from as low as 1 µg/l (e.g. several free terpenes) to more than 50,000 µg/l (e.g. isoamyl alcohol and ethyl
hydrogen succinate). In Table 3, a summary of these results is shown for the volatiles grouped into
different chemical classes (alcohols, esters, acids) including the minimum and maximum concentrations
for all the wines, the mean, standard deviation (SD), and coefficient of variation (CV) of the volatiles. In
order to assess the influence of the compounds studied on overall wine aroma, the odour activity values
(OAV) were also calculated on the average value of each volatile. As odour thresholds are affected by
additive, synergic and antagonistic effects of the volatile compounds in a matrix, the identification of the
most powerful odorants only on the basis of their OAV values has been considered as a tentative study in
order to explore the compositional basis of these Verdelho Queensland wines which have not been
characterised before.
In addition, the terpene profiles for each of the wines were analysed, calculated as the total, free and
bound fractions, and the results are shown in Table 4.
3.2.2. Alcohols
Of the chemical classes, the C6-alcohols identified were found to significantly differ in concentration
between wine samples. In particular, cis-3-hexenol was present between wines at levels above their
sensory detection thresholds, suggesting that this alcohol plays a role in the aroma of certain Verdelho
wines, contributing “green”, “grass” and “leafy” notes to the wine bouquet (Gómez-Míguez, et al., 2007;
Culleré et al., 2004; Guth & Sies, 2001). Levels and relationships between C6-alcohol compounds have
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been found to be characteristic of the grape variety (Versini, Orriols, & Dalla Serra, 1994). In our study,
all the Verdelho wine samples analysed showed the trans form of 3-hexenol to be present in higher
concentrations than the cis form, results which are in accordance with findings published by other
research groups for different grape varieties (García-Carpintero, Sánchez-Palomo, Gómez Gallego, &
González-Viñas, 2011).
Alcohols may have intense odours that can play an active role in wine aroma. In particular, higher
alcohols, at concentrations less than 300 mg/l (as a sum) certainly contribute a desirable level of
complexity to wine flavour, while at higher levels, their penetrating odours can mask the wines aromatic
finesse, with a detrimental effect on wine quality (Rapp & Versini, 1996). In our samples, the
concentration of total alcohols, in which the higher alcohol amounts have played a large role, ranged
between 115 and 220 mg/l and hence positively contributed to wine aroma. Of the three higher alcohols,
only 1-butanol was found to be significantly different between samples, and only 3-methyl-1-butanol
showed a level of odour activity value (OAV=3.8) that may have contributed to the wine aroma with a
“fusel”, “alcohol” note (Tufariello et al., 2012; Gómez-Míguez et al., 2007). Furthermore, the other two
alcohols that may make a potentially important contribution to the wine bouquet, showing an OAV
greater than 1, were the fusel alcohol 2-phenylethyl alcohol and the phenol 2-methoxy-4-vinylphenol.
These two compounds may contribute to pleasant ‘rose-like’ and spicy aroma nuances in wine. The latter,
a yeast metabolite of feroulic acid, was also found to be significantly different between the samples
(p<0.01) (Etiévant, 1991).
3.2.3. Esters
The presence of esters in wine originates mainly from yeast metabolism during the alcoholic
fermentation, but some of them have also been found in small amounts in the grape berry (Ribéreau-
Gayon, Glories, Maujean, & Dubourdieu, 2007). This chemical group of compounds is considered to be
the major contributor of fruity notes to the aroma of young wines and, in particular, ethyl esters of organic
acids are the most abundant, followed by acetates and ethyl esters of fatty acids (Etiévant, 1991; Rapp &
Versini, 1996). During wine ageing, the wine ester profile is subject to changes in concentration, due to
ongoing chemical esterification and hydrolysis reactions (Pérez-Coello, Martin-Alvarez, & Cabezudo
1999).
In our study, the ester group showed the most significant variability among the wine samples. In
particular, two ethyl esters of organic acids, namely ethyl hydrogen succinate and ethyl lactate, showed
the highest concentrations, affecting the total amount of this class of compounds. Medium-chain fatty
acid ethyl esters, such as ethyl hexanoate, ethyl octanoate, and ethyl decanoate, together with some
acetates, such as isoamyl acetate and 2-phenylethyl acetate, were found to be significantly different in the
10
samples with an OAV well above the odour threshold, especially for ethyl hexanoate and isoamyl acetate,
which showed the highest odour activity values (OAV=106 and 241 respectively). The ester compound 2-
phenylethyl acetate has been described as an effective enhancer for the “floral” and “sweet-like” notes in
young white wines, especially if associated with other compounds that have a “sweet” aroma, such as
isoamyl acetate (Campo, Ferreira, Escudero, & Cacho, 2005). In our work, these two acetates showed
OAV values well above their odour thresholds, confirming an active contribution to the sensory
properties of these Verdelho wines.
3.2.4. Acids
Although there are many different types of acids found in wine, fatty acids are considered to be the most
likely of this class of compounds to contribute to wine aroma (Etiévant, 1991). Fatty acids contribute to
either the fresh flavour of wine if they are present in the correct amount or to an unpleasant flavour if they
are in excess, and they can also help to modify the perception of other taste sensations (Ribéreau-Gayon
et al., 2007). In our samples, the amount of medium-chain fatty acids followed the trend of the
corresponding ethyl esters due to their common biosynthetic pathway (Soumalainen & Lehtonen, 1979).
In particular, hexanoic acid, octanoic acid and decanoic acid were detected at concentrations above their
sensory threshold level with an OAV greater than 1, which is likely to be detectable in the wines. At the
same time, short-chain fatty acids, such as isobutyric acid, butyric acid, and 3-methylbutyric acid, showed
an OAV>1, and with concentrations that differed significantly between samples, which might lead to
differences in their contribution to the wines aroma. At the concentrations found, fatty acids can
contribute “cheese” or “fatty” notes to the wines aroma (Rocha, Rodrigues, Coutinho, Delgadillo, &
Coimbra, 2004; Miranda-Lopez, Libbey, Watson, & Mc Daniel, 1992).
Pearson’s correlation (pair-wise) between chemical variables was also undertaken for the chemical
concentration values (data not shown). Extremely high correlations have been found between the total
amount of each chemical group and the volatile compound most representative of the group: total
alcohols and 3-methyl-1-butanol (r = 0.99), total esters and ethyl hydrogen succinate (r = 0.96). High
collinearity was also observed between some volatile compounds, specifically between 2-methyl-
propanol and ethyl lactate (r = 0.86) and between diethyl-succinate and 1-methylpropyl pentanoate (r =
0.91). The high correlation observed between some of the volatile compounds probably arises from the
similarity in biochemical pathway from which these compounds are derived. For example, ethyl
hexanoate, hexyl acetate, hexanoic acid and octanoic acid all showed a positive correlation value (r ≥
0.87), probably due to the fact that the biosynthesis of those esters is analogous to the synthesis of fatty
acids, that is they originate primarily from yeast metabolism during the fermentation (Suomalainen &
Lethtonen, 1979; Etiévant, 1991). On the other hand, the concentrations of diethyl succinate and ethyl
11
lactate have been reported to increase in the case of malolactic fermentation of wines (Ugliano & Moio,
2005). Similar biochemical pathways could also explain the extremely high correlation (r = 0.97) found
between the two long-chian fatty acids, tetradecanoic acid and pentadecanoic acid, and between the two
alcohols 2-phenylethanol and tyrosol (r = 0.89). Negative correlations resulted between isoamyl acetate
and ethyl lactate, 1-hexanol and diethyl succinate (r ≤ -0.88).
3.2.5. Terpenes
The structurally diverse terpenes play a significant role not only in the aroma of floral varieties, such as
Muscat, Gewürztraminer, Riesling, Auxerrois, Scheurebe, Muller-Thurgau, but also other varieties that
are not usually considered to be floral, such as Pinot Gris and Chardonnay (Dziadas & Jelen, 2010;
Bordiga, Rinaldi, Locatelli, Piana, Travaglia, Coïsson, & Arlorio, 2013). In particular, the monoterpene
content is considered a positive wine quality factor, since it is characteristic of the grape variety and it is
responsible for some typical cultivar nuances that are not affected by the fermentation process. It has been
well documented that the major part of the monoterpenes occurring in grapes and wines are not present in
their free form, but are instead bound with glucose or other sugars. Bound monoterpenes do not
contribute directly to the aroma, but they are a reservoir of odourless precursors of flavour. Even though
the bound form is quantitatively the most important, only the free form of terpenes show a floral and
citric odour contribution related to wine quality (Mateo & Jimenez, 2000; Câmara, Herberth, Marques, &
Alves, 2004; Câmara, Alves, & Marques, 2007; García-Carpintero et al., 2011). In Table 4 the
concentrations of the main monoterpenes detected in the free form and after enzyme hydrolysis are shown
for each of the Verdelho wines analysed.
With a range from 59.4 µg/l to 173 µg/l, the total amount of free monoterpenes detected confirm that
Verdelho is a neutral variety, and the presence of monoterpenes is likely to play only a minimal role in
determining the wine flavour (Mateo & Jimenez, 2000). β-Linalool and α-terpineol were markedly the
most abundant free monoterpenes, with sample VD3 showing the lowest amounts and VD7 the highest
amounts for these two monoterpenes. Only β-linalool showed significant differences between the
samples, and an odour active value greater than 1 (data not shown). These results confirm the findings
from other authors who have studied Verdelho wines originating from other countries, for which β-
linalool was the most abundant monoterpene and showed a potential discrimination sensory power,
contributing to the ‘floral’ aroma (Campo et al., 2005; Câmara et al., 2004). Lastly, in our Verdelho
samples, geraniol and nerol in the bound form were found to be more abundant than their free form, for
almost all the wine samples analysed. These results are in accordance with other studies of bound
monoterpenes in wines coming from both neutral and aromatic varieties (García-Carpintero et al., 2011;
Mateo & Jimenez, 2000; Krammer, Winterhalter, Schwab, & Schreier, 1991).
12
3.3. Quantitative descriptive sensory analysis
After an initial informal tasting, five of the eight Verdelho wines (VD1, VD2, VD3, VD5, VD6), which
were considered to be characteristic of the variety, were selected for further evaluation using descriptive
sensory analysis techniques.
A trained panel rated each wine, in triplicate, for the intensity of twenty-one (21) sensory attributes
previously developed during training sessions, as shown in Table 1, using a six point scale (anchored
from low/none - high). Reference standards utilised for aroma attributes are also shown. The descriptive
sensory results were subjected to an analysis of variance (ANOVA), and nine of the twenty-two sensory
attributes were found to be significantly different (p < 0.05) between the wines. The results are shown in
Figure 1 as two spider-web plots, divided into appearance and mouthfeel/palate attributes (Fig. 1A) and
aroma attributes (Fig. 1B).
The data confirmed that the wines originating from the Verdelho variety produced in the Granite Belt
region are characterised by a high “brilliant/clean” appearance and “flavour intensity”, in which
“crispness (or acidity)” and “persistence” are the dominant descriptors. For the aroma, the wines are
characterised as intense, with “tree-fruit” and “pungency” as dominant descriptors, together with some
“herbaceous” and “rockmelon” notes.
Regarding the significant differences between the wines, VD2 was found to show a high level of the
“floral/perfumed” attribute, likely due to the higher levels of some potent odorants, such as 2-phenylethyl
alcohol and 2-phenylethyl acetate, found for this sample. VD3 showed the largest “estery” flavour
attribute, a result supported by high levels of 3-ethoxy-1-propanol, 4-methyl-3-hexanol, isoamyl acetate,
ethyl-3-hydroxybutanoate, diethyl malate, and ethyl hydrogen succinate found for this wine (data not
shown). These compounds have been described as being reminiscent of banana, fruity, grape-like, apple
skin like, sugar and sweet aromas (Pereira, Chaco & Marquez, 2014; Tufariello et al., 2012; Gómez-
Míguez et al. 2007). Furthermore, VD2 and VD3 showed high scores for the “hotness” attribute, which
may be linked to the higher value of alcohol content measured for these two samples.
High scores for “floral/perfumed” and “tropical fruit” attributes were also found for VD3, at levels that
were similar to those of sample VD5, the latter being characterised by the highest values of medium chain
fatty acid ethyl esters. VD5 also showed the most “golden” colour, “tropical fruit” and “passionfruit”
aromas, together with the highest level of “sweetness” and the lowest “hot” attributes. VD6 was
characterised by the highest level of the “sulphides” note, together with a high level of the “golden”
appearance attribute. For this sample, the colour as measured by the optical density (O.D.) at 420 nm was
already highlighted as being a high value compared to the other wines.
13
4. Conclusions
In this work, the combination of SPE techniques with GC-MS, together with descriptive sensory analysis
has successfully allowed a complete analysis of the volatile compounds and sensory characterisation of
the Verdelho wines produced in the Granite Belt region of the Australian state of Queensland. The study
has revealed that these wines have a complex chemical profile with a rich aromatic composition. The key
volatile compounds that mostly contributed to the Verdelho wines aroma are related to fruity sweet notes
(ethyl esters and acetates), grass notes (3-hexenol), floral aromas (2-phenylethanol and B-linalool) and
cheesy aromas (fatty acids). The sensory analysis confirmed that the Australian Verdelho wines produced
in this region are characterised by high flavour and aroma intensities, crispy and persistent, with “tree-
fruit” as the dominant descriptor, together with a contribution of “herbaceous” and “rockmelon”
attributes. By contrast, differences in “tropical fruit” and “passionfruit”, together with “estery” and “floral
attributes” have been found. Further investigations on a more extensive set together with different
vintages of Verdelho wines produced in the Granite Belt will be needed to confirm these results in view
of its identity improvement and promotion.
Acknowledgments
The authors are grateful to the University of Queensland (UQ-NSRSF-2012003083) and the University of
Bologna (Marco Polo project A2230Z; RER project 124, PSR 2007/2013) for financial support, and the
Department of Agriculture Forest and Fishery (DAFF) for wine tasting panel participation and provision
of facilities and laboratories. Harrington Glen Estate, Hidden Creek, Ravens Croft Wines, Ridgemill
Estate, Robert Channon Wines, Rumbalara Estate Wines, Sirromet Wines, and Summit Estate Wines are
gratefully acknowledged for providing wine samples.
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Table 1. Sensory attributes selected for descriptive sensory analysis and composition of the corresponding
reference standards.
Verbal definitions Reference standard
Appearance attribute
Golden The level of colour, from colourless to light golden. No standard.
Green tint A slightly green hue in the colour of the wine. No standard.
Brilliant/clean Clear, with no haze or cloudiness. No standard.
Aroma attribute
Pungency Sensation of irritation/burning/tickling in the nose, associated with vinegar, SO2. 5 mL of pure white vinegar + 6 drops of SO2 (0.5%)
Floral/ Perfumed Sweet aroma of jasmine, frangipani flowers. 5 white jasmine and 1 white frangipani flowers*
Estery Aroma of bubblegum, artificial fruit. 10 mg of strawberry flavoured bubblegum
Tree Fruit Aroma of fresh peach, nectarine, apricot, pear, apple (stone fruit/pome fruit). 10 mg each of fresh peach, nectarine and apricot slices
Rock melon Aroma of fresh, ripe rockmelon. 20 mg of fresh rock melon
Tropical Fruit Aroma of tropical fruit like banana, pineapple, pawpaw, lychee. 10 mg each of fresh banana and canned pinapple slices
Passionfruit Aroma of fresh cut passionfruit. Small piece of fresh passionfruit skin (0.5 cm) and pulp (ca. 3 seeds)
Herbaceous Aroma of a slightly under-ripe green melon, green apple, cut grass, green vegetables. 20 mg of fresh green melon
Sulphides Aroma of burnt match, rubber, rotten eggs, plastic, wet dog. 20 mg of rubber piece
Chemical/Solvent Chemical (nail polish remover). 4 drops of ethyl acetate std*
Flavour attribute
Viscosity/body Watery to viscous, the weight and fullness of wine as it crosses the palate. No standard.
Crispness A crisp, acidic, tangy flavour, degree of sourness. No standard.
Sweetness A sweet taste. No standard.
Bitterness A bitter taste. No standard.
Hotness (heat) a warm sensation in the mouth, burns with heat in the back of the throat. No standard.
Flavour intensity The relative level of flavour in the mouth.. No standard.
Persistence The length of time that flavour remains on the palate after spitting. No standard.
Astringency The degree of drying/roughing mouth-feel sensation experienced after spitting. No standard.
All standards were freshly prepared into standard tasting glasses (ISO 3591) with lids.
* Quantities specified are those added to 40 mL of neutral young white wine.
19
Table 2. General composition of selected Granite Belt Verdelho wines from vintage 2012. Mean
concentrations and relative standard deviations.
Wine Code alcohol content pH colour
% v/v 420 nm
VD1 12.5 2.85 150 ± 1.09 4.77 ± 1.63 0.046 1.90 ± 0.01 0.48 ± 0.00
VD2 13.7 2.68 180 ± 5.21 10.6 ± 0.94 0.028 1.41 ± 0.00 0.44 ± 0.03
VD3 13.0 3.14 88.3 ± 1.41 13.3 ± 0.30 0.029 1.80 ± 0.01 0.38 ± 0.04
VD4 12.5 2.85 168 ± 3.08 30.2 ± 2.23 0.027 2.12 ± 0.00 0.53 ± 0.00
VD5 12.0 3.34 161 ± 2.56 26.8 ± 0.41 0.045 2.38 ± 0.10 0.56 ± 0.05
VD6 12.0 3.14 83.6 ± 0.19 12.7 ± 0.23 0.056 2.39 ± 0.43 0.35 ± 0.20
VD7 13.5 3.24 231 ± 14.2 30.4 ± 0.04 0.051 1.61 ± 0.39 0.32 ± 0.25
VD8 13.0 2.92 124 ± 1.00 18.1 ± 2.49 0.032 1.25 ± 0.01 0.37 ± 0.01
total SO2 free SO2 malic acid lactic acid
mg/L mg/L g/L g/L
20
Table 3. Minimum, maximum and mean volatile concentrations, odour threshold (OTH) and relative
odour active value (OAV) of volatile compounds found in Granite Belt Verdelho wines.
Identa
min max mean SD CV OTHb
OAVc
(p<0.01)
(µg/L) (µg/L) (µg/L) (µg/L) % (µg/L) (µg/L)
Alcohols
C 6 Alcohols
1-Hexanol S, MS 782 2141 1224 421 34% 40000 0.3 *
trans -3-Hexenol S, MS 39 226 99 56 57% nd nd *
cis -3-Hexenol S, MS 37 127 70 27 38% 40 1.8 *
Other alcohols
2-Methyl-1-propanol S, MS 9358 34518 19024 7846 41% 4080 0.5 -
1-Butanol S, MS 516 1544 863 291 34% 150000 0.0 *
3-Methyl-1-butanol S, MS 89991 143277 113240 15543 14% 30000 3.8 -
3-Methyl-3-buten-1-ol S, MS 16 39 28 8 29% nd nd -
1-Pentanol S, MS 24 45 35 8 23% nd nd *
3-Methyl-1-pentanol S, MS 40 110 70 24 35% nd nd *
2-Methyl-3-pentanol MS 5 41 18 12 66% nd nd *
3-Ethoxy-1-Propanol S, MS 22 848 321 327 102% nd nd *
4-Methyl-3-hexanol MS 73 263 120 47 39% nd nd -
3-(Methylthio)-1-propanol MS 73 191 132 34 26% 500 0.3 -
Benzyl alcohol S, MS 30 266 117 85 73% 200000 0.0 *
2-Phenylethyl alcohol S, MS 8110 16206 10662 2537 24% 10000 1.1 -
2-Methoxy-4-vinylphenol MS 13 224 68 59 86% 40 1.7 *
4-Hydroxy-benzeneethanol S, MS 6307 20461 12187 3768 31% nd nd *
Total alcohols 115434 220525 158279 25121 16% nd nd -
Esters
Ethyl Esters
Ethyl hexanoate S, MS 921 2077 1478 336 23% 14 106 *
Ethyl lactate S, MS 4200 11964 7870 2562 33% 154000 0.1 *
Ethyl octanoate S, MS 1022 2513 1695 472 28% 240 7.1 *
Ethyl-3-hydroxy-butanoate S, MS 163 462 308 80 26% 20000 0.0 *
Ethyl decanoate S, MS 284 725 537 147 27% 200 2.7 *
Diethyl succinate S, MS 267 1115 658 273 42% 200000 0.0 *
Diethyl malate MS 352 1767 1158 424 37% 10000 0.1 *
1-methylpropyl pentanoate MS 165 726 434 147 34% nd nd -
2-Ethylhexyl salicylate MS 16 106 50 28 55% nd nd -
Ethyl hydrogen succinate MS 65757 157015 101078 23468 23% nd nd -
Diethyl malonate MS 34 100 62 23 38% nd nd *
Acetates
Isoamyl acetate S, MS 2411 11534 7228 2608 36% 30 241 *
Hexyl acetate S, MS 70 387 260 87 33% 670 0.4 *
Isopropyl acetate S, MS 276 691 447 142 32% nd nd *
2-Phenylethyl acetate S, MS 138 1017 428 255 60% 250 1.7 *
Total esters 76077 192199 123691 23664 19% nd nd -
Acids
Propanoic acid S, MS 935 2040 1367 348 25% 8100 0.2 *
Isobutyric acid S, MS 1609 3769 2766 633 23% 2300 1.2 *
Butyric acid S, MS 1264 2508 1870 345 18% 400 4.7 *
3-Methylbutyric acid S, MS 283 973 670 212 32% 250 2.7 *
Neodecanoic acid MS 313 1776 750 422 56% nd nd *
Hexanoic acid S, MS 4389 6814 5448 742 14% 420 13 -
Octanoic Acid S, MS 5940 9297 7427 1012 14% 2200 3.4 -
n-Decanoic acid S, MS 2087 3635 2747 495 18% 1400 2.0 -
Dodecanoic acid S, MS 53 118 88 21 24% 6100 0.0 -
Phenylacetic acid MS 10 221 55 59 107% 1000 0.1 *
Tetradecanoic acid MS 104 240 168 46 27% nd nd -
Pentadecanoic acid S, MS 50 150 98 30 30% nd nd -
n-Hexadecanoic acid S, MS 384 857 590 153 26% nd nd -
Total acids 17423 32398 24044 2396 10% nd nd -
Others
3-hydroxy-2-butanone MS 50 816 253 250 99% 150000 0.0 *
2-octanone S, MS 52 69 63 4 7% nd nd -
ƴ-Butyrolactone S, MS 279 961 654 186 28% 20000 0.0 -
bOdour threshold reported in literature (Cullere et al., 2004; Vilanova et al., 2010; Tufariello et al., 2012; Gómez-Míguez et al. 2007).
cOdour activity value calculated as a ratio of the mean concentration to the sensory detection threshold of the compounds.
* Statistical differences at p < 0.01 according to the Tukey's test.
nd, not determined. For these compounds odour detection limits are not reported in literature.
aMethod of identification: S, by comparison of mass spectrum and retention time with those of the standard compounds; MS, by comparison
of mass spectrum with those included in the NIST 2.0 and Wiley 7 libraries.
21
Table 4. Total, free and bound monoterpene contents (means and standard deviations expressed in µg/l) in
Granite Belt Verdelho wines (n=2).
Table 4. Total, free and bound monoterpene contents (means and standard deviations expressed in µg/L) in Granite Belt Verdelho wines (n=2).
mean SD mean SD mean SD mean SD mean SD mean SD mean SD mean SD
trans -Linalool oxide total 10.7 ± 0.01 8.77 ± 0.37 6.83 ± 0.56 9.66 ± 0.22 8.80 ± 0.22 10.3 ± 1.11 6.88 ± 1.18 7.35 ± 1.01
free 10.7 ± 0.01 6.53 ± 0.60 2.67 ± 0.80 9.66 ± 1.65 6.13 ± 0.33 9.54 ± 2.11 2.41 ± 0.03 2.47 ± 0.53
bound 0.00 ± 0.00 2.23 ± 0.23 4.16 ± 1.36 0.00 ± 0.00 2.67 ± 0.11 0.80 ± 0.22 4.46 ± 1.15 4.88 ± 1.54
cis -Linalool oxide total 6.90 ± 0.29 6.14 ± 0.05 2.10 ± 0.17 5.33 ± 0.11 7.71 ± 0.51 6.23 ± 0.05 3.39 ± 0.13 2.11 ± 0.12
free 6.90 ± 0.13 4.92 ± 0.45 1.94 ± 0.32 5.33 ± 1.32 5.75 ± 0.23 6.23 ± 2.18 2.13 ± 0.02 1.19 ± 0.54
bound 0.00 ± 0.00 1.22 ± 0.40 0.15 ± 0.49 0.00 ± 0.00 1.95 ± 0.28 0.00 ± 0.00 1.26 ± 0.11 0.92 ± 0.66
β -Linalool* total 36.2 ± 0.63 41.2 ± 0.11 29.2 ± 0.42 16.2 ± 0.73 49.5 ± 0.97 33.6 ± 1.03 91.9 ± 4.24 27.6 ± 2.34
free 35.4 ± 0.82 39.8 ± 0.19 14.2 ± 0.28 15.6 ± 0.24 47.0 ± 1.91 28.2 ± 1.66 80.6 ± 3.14 20.4 ± 3.90
bound 0.75 ± 0.45 1.36 ± 0.08 15.0 ± 0.14 0.56 ± 0.97 2.54 ± 0.94 5.45 ± 0.63 11.2 ± 7.38 7.22 ± 6.24
Isopulegol total 0.00 ± 0.00 8.17 ± 0.21 7.35 ± 1.04 8.39 ± 0.54 9.62 ± 0.15 8.94 ± 0.34 11.0 ± 0.37 7.54 ± 0.91
free 0.00 ± 0.00 6.74 ± 0.22 5.53 ± 0.34 7.02 ± 0.25 7.91 ± 0.03 7.24 ± 1.15 7.90 ± 0.13 4.21 ± 1.47
bound 0.00 ± 0.00 1.43 ± 0.43 1.82 ± 0.70 1.36 ± 0.80 1.71 ± 0.12 1.70 ± 0.81 3.10 ± 0.50 3.33 ± 2.38
α -Terpineol total 34.6 ± 0.31 42.7 ± 2.34 30.2 ± 1.60 26.4 ± 0.19 48.6 ± 8.38 37.1 ± 1.84 59.0 ± 6.88 33.6 ± 2.77
free 34.6 ± 0.04 38.0 ± 3.14 13.4 ± 1.14 20.2 ± 0.44 42.7 ± 4.43 29.4 ± 3.93 57.7 ± 1.15 23.0 ± 5.92
bound 0.00 ± 0.00 4.64 ± 0.80 16.8 ± 0.46 6.29 ± 0.62 5.93 ± 3.95 7.74 ± 2.09 1.28 ± 8.03 10.6 ± 3.15
Citronellol total 6.14 ± 0.05 6.11 ± 0.50 7.38 ± 0.28 5.48 ± 0.09 10.1 ± 1.75 8.82 ± 1.42 10.6 ± 0.38 7.15 ± 0.19
free 5.95 ± 0.02 5.53 ± 0.84 6.92 ± 0.24 5.48 ± 0.32 9.92 ± 0.50 8.52 ± 2.21 8.72 ± 0.08 4.44 ± 1.73
bound 0.19 ± 0.07 0.58 ± 0.34 0.46 ± 0.04 0.00 ± 0.00 0.13 ± 1.25 0.30 ± 0.20 1.92 ± 0.30 2.71 ± 1.92
Geraniol total 5.15 ± 0.74 4.86 ± 0.25 3.90 ± 0.29 3.11 ± 0.02 8.01 ± 1.55 5.56 ± 0.59 8.77 ± 0.07 3.52 ± 0.35
free 1.83 ± 0.01 2.27 ± 0.29 1.05 ± 0.28 0.81 ± 0.04 4.14 ± 0.00 2.06 ± 0.56 4.86 ± 0.78 1.63 ± 0.26
bound 3.32 ± 0.76 2.59 ± 0.03 2.84 ± 0.56 2.30 ± 0.06 3.87 ± 1.56 3.50 ± 0.03 3.91 ± 0.71 1.89 ± 0.62
Nerol total 8.32 ± 0.21 7.34 ± 0.17 6.32 ± 0.78 5.03 ± 0.07 15.6 ± 2.70 10.6 ± 2.31 19.3 ± 0.82 6.50 ± 1.11
free 3.46 ± 0.35 2.69 ± 0.34 2.98 ± 0.08 1.53 ± 0.06 4.95 ± 0.08 3.21 ± 0.94 8.40 ± 1.09 2.13 ± 0.93
bound 4.86 ± 0.14 4.65 ± 0.51 3.33 ± 0.86 3.50 ± 0.01 10.6 ± 2.62 7.39 ± 1.37 10.9 ± 1.91 4.36 ± 0.18
Total terpenes total 108 ± 1.72 125 ± 2.31 93.2 ± 3.02 79.2 ± 0.45 158 ± 15.9 121 ± 8.59 211 ± 11.7 95.3 ± 1.04
free 98.9 ± 1.32 107 ± 2.95 48.7 ± 0.21 65.6 ± 2.89 128 ± 7.45 94.3 ± 14.7 173 ± 4.67 59.4 ± 15.3
bound 9.12 ± 2.27 18.7 ± 0.64 44.5 ± 2.81 14.0 ± 2.43 29.4 ± 8.49 26.8 ± 6.16 38.1 ± 16.4 35.9 ± 16.3
* Monoterpenes with an OAV>1.
VD1 VD2 VD3 VD4 VD5 VD6 VD7 VD8
22
Figure 1. Appearence and mouthfeel/palate attributes (A) and aroma attributes (B) for the five Verdelho
wines subjected to the Sensory Descriptive Analysis (*significant different descriptors for p < 0.05,
according to the Tukey’s test).
A
B
RESEARCH HIGHLIGHTS
• The Queensland Verdelho volatile profile has been characterised for the first
time.
• A sensory descriptive analysis has also been undertaken for these wines.
• SPE-GC/MS analysis identified key compounds contributing to Verdelho
flavour.
• Sensory descriptive analysis underlined characteristic attributes for the wines.
• These results lay the foundation for further study of Verdelho as a dry wine
style.