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:

f.sonni@uq.edu.au

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

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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

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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.