## 3 Results and Discussion
### Quantification of Phenolic Compounds in Must and Wine  
Three groups of phenolic compounds (phenolic acids, flavan-3-ols and flavonoids) were detected by UPLC-PDA analysis in Aurora cv. must and wine. The concentration of these compounds is very important in understanding the antioxidant potency of white wines. The content of those chemicals, crucial for wine quality (Table 2), ranged from 207.8 to 287.2 mg/L in the must and from 201.0 to 329.4 mg/L in the final wine (variants fermented at 12 and 20 \({}^{\circ}\)C, respectively). Wine phenolic composition depends on the grapes from which they are partly extracted, and on the vnification conditions [3], including temperature, mixing, parameters of the fermentation vessel, pre-fermentative skin contact maceration, ethanol concentration, SO\({}_{2}\), yeast strain, pH, and pectolytic enzymes [25]. Total phenolic compounds amounted to 312.5 mg/L in the fresh must. Fermentation triggered different changes in the content of phenolics but those caused by temperature were not significant (\(p>0.05\)) in either fresh or matured wine. Contrary to that, the use of different yeast strains resulted in significant changes (\(p<0.05\)) in the content of polyphenols. Both _S. cerevisiae_ strains (SIHA(r) Cryarone and Challenge Aroma White) produced wines richest in polyphenols. The wines fermented spontaneously and with _S. bayanus_ were characterized by a lower content of total phenolics. [PERSON] et al. [3] investigated white wines from different grape cultivars, grown in southern Poland, in which total phenolic content ranged from 280 to 510 mg of gallic acid/L. Aurore wine produced by fermentation with _S. cerevisiae_ D 576 contained 300 mg of gallic acid/L. [PERSON] et al. [4] reported total polyphenol content in Aurore wine amounting to 463.0 mg of catechin/L. Red wine is known to be 10 times richer in polyphenolics and to have greater antioxidant capacity than white wine, and this variability is due to red wine grape must fermentation [26; 27]. This is why white wine receives much less attention than red wine. Flavan-3-ols were the major phenolics group in Aurore wine and they constituted almost 76% of total must phenolics. The must contained 236.4 mg of flavan-3-ols per L. Contrary to yeast strain, the temperature of fermentation did not induce significant (\(p>0.05\)) changes in flavan-3-ol content. The lowest concentration of flavan-3-ols was detected in the wine obtained with _S. bayanus_ (154.4 and 183.3 mg/L, respectively for fresh and aged wine), and the wine fermented spontaneously (162.5 and 198.2 mg/L). The wines produced with _S. cerevisiae_ were characterized by the highest amount of flavan-3-ols. This was particularly visible for the SIHA(r) Cryarone strain that yielded wine in which these compounds were present at 290.1 and 301.7 mg/L in the fresh and matured wine, respectively. An increase in flavan-3-ols during maturation was noticed for all variants, as compared with the wine immediately after fermentation. Flavan-3-ols are important for wine properties. Catechins and procyanidims strongly affect the susceptibility of white wine to browning, as flavan-3-ols may undergo oxidation and polymerization. They also have a direct impact on the complexity of wine taste and mouthfeel and are responsible for wine bitterness and astringency [28; 29; 30]. Additionally, [PERSON] et al. [31] reported higher levels of flavan-3-ol sulfonated in aged wines compared to native flavan-3-ol monomers in most of the samples of young wines. [PERSON] et al. [31] postulated that these sulfonated flavanols arise from a cleavage of an interflacan bond of proanthocyanidims and nucleophilic attack by SO\({}_{2}\) on C4 carbocation. These results demonstrate that the sulfonation of tannins readily occurs under wine aging conditions, releasing flavan-3-ol sulfonates in significant quantities.