Abstract
Summary: The aroma compounds of two bottled monovarietal wines (Pinot Gris and Pinot Noir) were investigated using bidimensional gas-chromatography coupled with time of flight mass spectrometry (HS-SPME-GCxGC-ToF/MS). Pinot Gris wines were characterized by compounds such as linalool, β-ionone and α-terpineol while Pinot Noir by β-damascenone, trans whiskey lactone and benzaldehyde.
Keywords: Pinot Gris, Pinot Noir, HS-SPME-GC x GC-TOF/MS
1.Introduction
Amongst many contributing factors that have been studied for the determination of wine quality, aroma, and flavour are considered to be the most important as they also set differences between a wide number of wines and wine styles produced throughout the world [1,2]. Wine aromas are characterized by complex interactions between the vineyard soil, geographical site, and climate characteristics, grape variety, and the technical conditions of winemaking. The knowledge of aromatic compositions of wines is of great interest as it is also highly related to the flavour. In addition, the hundreds of volatile compounds that define the wine aroma also relate to the acceptance or rejection of the wines by the consumers. Comprehensive two-dimensional gas chromatography (GCxGC) has emerged as a powerful technique for identifying a substantially larger number of volatile compounds with enhanced separation efficiency compared to one-dimensional GC, reliable in both qualitative and quantitative analysis, ability to detect low concentration and thus provides a more detailed information on the wine volatile fingerprint [3]. Several studies have been carried out to associate the wine volatiles with the grape variety which is also the aim of this study.
2.Materials and Methods
Pinot Gris and Pinot Noir bottles from different geographical origins were kindly provided by FruitService S.r.l., a South Tyrolean trading company (Bolzano, Italy).
The volatile compounds were characterized by Head Space Solid-Phase Microextraction combined with Comprehensive Two-Dimensional GC coupled to Time-Of-Flight Mass Spectrometry (HS-SPME-GCxGC-ToF/MS) using a Flow-Modulated interface between the two capillary columns in a Pegasus® Flux BT 4D (LECO Corporation, Germany). An internal standard (2-methyl-3-pentanol) was used for checking the repeatability. The injection was carried out in a splitless mode, and the flow rate was 1 ml/min over a polar MEGA- WAX Spirit column 40m/0.18mm/0.30µm (first dimension, MEGA s.r.l) and a 1.2m/0.1mm/0.1µm MEGA 1-HT (second dimension, MEGA s.r.l). These parameters were slightly adapted methods from published reports [4]. Automatic alignment of the dataset was done using the processing software ChromaTOF® (LECO Corporation, Berlin, Germany) ver.2021. These obtained final datasets were inspected and refined prior to the statistical analysis.
3.Results
The GC chromatograms for both the Pinot Gris and Pinot Noir wine samples are reported in Figure 1&2. The volatile profiles have been analysed by Principal Component Analysis (PCA) for both varieties (Figure 3&4). For Pinot Gris wines, the replicate samples of each origin were well grouped. The origins were clearly separated mostly along the first principal component (Figure 3). Wines from New Zealand (Gisborne) were characterized by 2,4-di-tert-butylphenol which is a very recently identified compound in wines sealed with synthetic closures and micro agglomerated cork and were also identified in white wine samples [6,7]. The wines from Puglia-Sicilia (Southern Italy) were characterized by the volatile compounds linalool and 3-hexanol,3-ethyl while the wines from Northern Italy, Veneto-Friuli were characterized by volatile compounds ethyl phenylacetate and benzaldehyde. The wines from South Africa Western Cape (Irrigated area) were characterized by 2,3-butanediol, ethyl hexanoate, α-terpineol, ethyl octanoate while the wines from dry land were more characterized by ethyl acetate, benzenebutanal, and phenylethyl acetate. The wines from New Zealand (Marlborough) were more correlated with ethyl dodecanoate , 2,3-butanediol , hexanoic acid and decanoic acid.
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Fig. 1&2 GCxGC chromatogram of Pinot Gris (left) and Pinot Noir (right) sample
For Pinot Noir wines, the replicates are grouped well in PC2 vs PC3 (Figure 4). Wines from both South Africa: Western Cape (dry land) and New Zealand showed similarity and were characterised by compounds like benzyl alcohol, trans whiskey lactone, benzaldehyde, 1-hexanol, and furfural. The Italian wines from both the Southern and Northern part were grouped together and correlated with the compounds nerolidol, 1-butanol, 3-methyl-acetate, butyraldehyde, and phenylethyl acetate. The Chilean wines were more characterized by phenol, 4-ethyl, α-terpeniol, β-damascenone, ethyl sorbate, and butanedioic acid, diethyl ester. The wines from Argentina were more characteristic of ethyl acetate, isoamyl lactate, 2,3-butanediol, acetic acid, and β-ionone.
Fig. 3&4. PCA biplot (PC1-PC2) left of Pinot Gris and (PC1-PC2, PC2-PC3) right of Pinot Noir wine samples and volatile compounds
4.Conclusion
The volatile compounds for both varieties from different origins/wineries were characterized. The volatile profiles were distinct for each variety from different countries. The wines have also been characterized for their sensory and phenolic profiles (not discussed here).
These preliminary data show that single-varietal wines of different geographic origins can differ significantly, which can lead to consumer confusion. To help producers and distributors achieve the goals of tailored commercial offerings, simplified "aroma maps" based on 2DGC chromatograms and accompanied by simple pictograms could be part of the information sheet (technical sheet) that the winery provides with the product. In this way, the information given to commercial stakeholders can be improved to meet sensory expectations related to the product offered.