# Different SO\({}_{2}\) Doses and the Impact on Amino Acid and Volatile Profiles of White Wines
## 3 Results and Discussion
### Volatile Organic Compound
#### 3.1.4 Principal Component Analysis of Volatile Organic Compounds during Bottle Ageing  
A principal component analysis (PCA) was performed to verify if the different SO\({}_{2}\) doses applied during aging could influence the VOCs profile of the wine. In order to build the PCA for each wine group (AV and BL) illustrated in Figures 2 and 3, the relative areas of the tentatively identified VOCs (Table 1) were used. These relative areas were normalized against the relative areas of the initial wine, according to [PERSON] et al., 2022 [PERSON] et al. (2022). Hence, the wine after fermentation (t = 0) is placed in PC1 = 0 and PC2 = 0. It is possible to observe that 74.96% and 66.65% of the system variance was explained by the 1 st and 2 nd principal components (PC1 and PC2, respectively) for AV wines and for BL wines, respectively. Figure 2: Principal component biplot illustrating the simultaneous projection of the wine and volatile organic compounds of Antão Vaz wine (AV). Black dot—initial wine; Black triangle—wines aging for 3 months; Black rhombus—wines aging for 6 months; Black cross—wines aging for 12 months; 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. Figure 2 illustrates the PCA for AV wines. PC1 separates the samples according to the aging time, explaining 43.33% of the system variability, and PC2 separates the samples regarding the application of SO\({}_{2}\), explaining 31.63% of the system variability. In the positive quadrant of PC1, samples aged for 12 months are clearly separated from the other wine samples. Along PC2, a fair separation of wines with 3 and 6 months can be observed, being the first ones mainly influenced by ethyl octanoate (23). However, for samples aged for 6 months, it is possible to observe a distinction of VOCs profile leading to wines well separated according to different SO\({}_{2}\) doses applied. The most similar samples to the previous ones (3 months of aging) are the samples with the application of higher doses of SO\({}_{2}\) (90 and 120 mg/L), suggesting a protection role of the samples against oxidation, and are characterized by isoamyl acetate (8). For the samples with no addition or addition of 30 mg/L of SO\({}_{2}\), samples were similar and mainly influenced by acetate 4-hexenoate (isomer) (17), decyl acetate (35), isoamyl decanoate (43), phenethyl alcohol (66) and nonanal (68). The wines stored with 60 mg/L of SO\({}_{2}\) were separated from the others and characterized by isoamyl butyrate (14). The wines aged for 12 months in the presence of 0, 30, 60, and 90 mg/L of SO\({}_{2}\) are very similar. Indeed, they are impacted by diethyl succinate (36), 2-propanol (53), and decanoic acid (71). Samples aged with 120 mg/L are more influenced by ethyl hexanoate (12). Figure 3 illustrates the PCA obtained for BL wines. PC1 separates the samples according to time of aging, explaining 49.99% of the system variability, and PC2 explaining 16.66% of the system variability, separates the samples according to the addition of SO\({}_{2}\). BL wines aged for 12 months are in the positive quadrant of PC1, clearly separated from other wines, and positively influenced by ethyl butyrate (5), isoamyl acetate (8), ethyl hexanoate (12), and isoamyl butyrate (14). However, BL wines without the addition of  
Figure 3: Principal component biplot illustrating the simultaneous projection of the wine and volatile organic compounds of Blend wine (BL). Black dot—initial wine; Black triangle—wines aging for 3 months; Black rhombus—wines aging for 6 months; Black cross—wines aging for 12 months; 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. SO\({}_{2}\) are on the positive side of both PC1 and PC2 and separated from the other samples aged for 12 months.