6 SUMMARY OF THE OBSERVATIONS
6.1.4 Principal component analysis of Volatile Organic Compounds
A principal component analysis (PCA) was performed to verify if the different antioxidant envi-ronments applied could influence the wine VOCs profile. For the construction of PCA for each wine variety Arinto, Gouveio and Síria, with different doses of SO2 or ascorbic acid the relative area of the tentatively identified VOCs (Table 6-3) were used.
It was possible to observed that 85.57% of the system variance was explained by the first and second principal components (PC1 = 71.94% and PC2 = 13.64%). The variety is the principal factor for wine distribution projected on PC1 and the SO2 doses applied presented a similar impact on both va-rieties on PC2, Figure 6-4. When comparing both vava-rieties Gouveio wines after fermentation with the application of 50 and 100 mg/L of SO2 lead to wines more similar, possible due to a less sensitivity to oxidation, comparing to Arinto wines.
Figure 6-4 Principal component biplot illustrating the simultaneous projection of the wine and volatile compounds of Arinto wines and Gouveio wines fermented with higher SO2 doses range. Black triangles – Gouveio wines; Black lozenges – Arinto wines; Dark blue dots – esters; Dark green dots – ethers; Yellow dots – ketones; Red dots – alcohols; Light blue dots – alde-hydes; Light grey dots – carboxylic acids; Purple dots – miscellaneous; Gray dots– unknowns.
For wines analysed after 6 months of short evolution, the relative areas were standardised against the relative areas of the initial wine (after fermentation). Therefore, the initial wine is in PC1 = 0 and PC2 = 0. It is possible to observed that 82.85% of the system variance was explained by the first and second principal components (PC1 = 77.13% and PC2 = 5.71%), Figure 6-5. In addition, it was pos-sible to observe that similar to the after fermentation results the wine variety is the principal factor of distinction (corresponding to PC1). Arinto wines were more sensitive to the combination of antioxida-tion condiantioxida-tions and Gouveio wines were more stable. For this variety the condiantioxida-tion without any anti-oxidant presents a completely different profile, maybe due to oxidative process. These results indicate that a possible reduction of SO2 application can be applied on Gouveio wines during fermentation or a short storage with low impact on VOCs profile. However, the same conclusion is not applicable to Arinto wines as the fermentation conditions seems to affect the VOCs profile evolution.
Figure 6-5 Principal component biplot illustrating the simultaneous projection of the wine and volatile compounds of Arinto wines and Gouveio wines fermented with higher SO2 doses range of evolution wines using wines after fermentation as refer-ence. Black triangles – Arinto wines; Black lozenges – Gouveio wines; Dark blue dots – esters; Dark green dots – ethers; Yel-low dots – ketones; Red dots – alcohols; Light blue dots – aldehydes; Light grey dots – carboxylic acids; Purple dots – miscel-laneous; Gray dots – unknowns; Orange shadow – wines fermented without SO2; Grey shadow – wines fermented with 50 mg/L of SO2; Blue shadow – wines fermented with 100 mg/L of SO2.
For wines after fermentation with the lowest SO2 doses, the PCA were also performed. It is pos-sible to observed that 85.26% of the system variance was explained by the first and second principal components (PC1 = 74.78% and PC2 = 10.49%). Also, in this case the variety is the principal factor for wine distribution been represented on PC1 and the SO2 doses applied on PC2, Figure 6-6. The results observed for Arinto wines are in accordance with the observation of Arinto wines fermented with the higher doses as the fermentation without SO2 giving a completely different VOCs profile to that wine upon SO2 doses.
Figure 6-6 Principal component biplot illustrating the simultaneous projection of the wine and volatile compounds of Arinto wines and Síria wines fermented with lower SO2 doses range. Black triangles – Arinto wines; Black lozenges – Síria wines;
Dark blue dots – esters; Dark green dots – ethers; Yellow dots – ketones; Red dots – alcohols; Light blue dots – aldehydes;
Light grey dots – carboxylic acids; Purple dots – miscellaneous; Gray dots – unknowns.
PCA was also performed for the same samples, using wines after fermentation as reference. It was possible to observed that 62.77% of the system variance was explained by the first and second principal components (PC1 = 54.79% and PC2 = 7.97%). Also, in this case the variety is the principal factor for wine distribution been represented on PC1 and the SO2 doses on PC2, as illustrated in Figure 6-7. In this case the Síria wines presented more sensitivity to VOCs composition regarding SO2 applica-tion on fermentaapplica-tion, however Arinto wines fermentaapplica-tion without SO2 application presented a higher differentiation on VOCs profile.
Regarding the second antioxidation condition after fermentation Arinto wines presented a higher distribution that occurs specially for the wines that fermented without any SO2 application.
Figure 6-7 Principal component biplot illustrating the simultaneous projection of the wine and volatile compounds of Arinto wines and Síria wines fermented with lower SO2 doses range of evolution wines using wines after fermentation as reference.
Black triangles – Arinto wines; Black lozenges – Síria wines; Dark blue dots – esters; Dark green dots – ethers; Yellow dots – ketones; Red dots – alcohols; Light blue dots – aldehydes; Light grey dots – carboxylic acids; Purple dots – miscellaneous;
Gray dots – unknowns; Orange shadow – wines fermented without SO2; Green shadow – wines fermented with 15 mg/L of SO2; Grey shadow – wines fermented with 30 mg/L of SO2; Blue shadow – wines fermented with 45 mg/L of SO2.
Regarding the application of ascorbic acid as a substitute of SO2, VOCs profile after fermenta-tion were used as reference, therefore placed on PC1 = 0 and PC2 = 0. The PCA analysis of these wines after evolution allow to observe that 69.45% of the system variance was explained by the first and second principal components (PC1 = 43.70% and PC2 = 25.75%). Also, in this case the SO2 application after fermentation is the principal factor for wine distribution being projected on PC1 and the variety on PC2, Figure 6-8. Arinto wines in this case showed to be more impacted by the antioxidant condi-tions, compared to Síria and Gouveio wines. The second antioxidant application on Gouveio and Síria wines lead to similar VOCs profile for each wine and the Síria wines presented a more variation from the other two varieties. The replacement of SO2 by ascorbic acid did not impact the VOCs profile of
Figure 6-8 Principal component biplot illustrating the simultaneous projection of the wine and volatile compounds of Arinto, Síria and Gouveio wines fermented with ascorbic acid of evolution wines using wines after fermentation as reference. Black triangles – Gouveio wines; Black lozenges – Arinto wines; Black squares – Síria wines; Dark blue dots – esters; Dark green dots – ethers; Yellow dots – ketones; Red dots – alcohols; Light blue dots – aldehydes; Light grey dots – carboxylic acids;
Purple dots – miscellaneous; Gray dots – unknowns; Orange shadow – wines fermented without SO2; Grey shadow – wines fermented with 50 mg/L of SO2; Blue shadow – wines fermented with 100 mg/L of SO2.
In this study it was observed that the short evolution of wines led to a reduction of esters in all varieties regardless of antioxidant conditions. PCA analyses of wines treated with the highest doses of SO2 (Gouveio and Arinto varieties) before and after fermentation, allow to observe that Arinto wines demonstrate a greater sensitivity to the applied conditions, although moderate. After a short evolu-tion, the VOCs profile of the Gouveio wines presented greater stability than the Arinto wines under the same conditions. Regarding wines fermented with lower doses (Arinto and Síria varieties) after fermentation, the VOCs profile of Arinto wines presented greater stability, except for the condition where no SO2 was applied. Comparing with a short evolution of the same varieties, Síria wines were less sensitivity, creating wines that are more similar to each other regardless the conditions applied during fermentation. When these three varieties (Arinto, Síria and Gouveio) were fermented with ascorbic acid, as a replacement for SO2 as antioxidants, and after a short evolution in the presence or
absence of SO2, it was observed that the Arinto variety was the one with the highest sensitivity to the second condition and both wines from Síria and Gouveio showed a similar VOCs profile regardless the presence or not of SO2. were more sensitive to evolution 6 months over lees.