## 3 Results and Discussion
### Adaptive Evolution-Mediated Changes in Resveratrol Concentrations  
Besides high tolerance to osmotic stress, enhanced levels of intracellular glycogen, or increased production of glycerol, another desirable feature of wine yeast strains is the ability to liberate glycosylated flavor precursors [2]. The latter greatly improves the sensory profile of wine and, in addition, some of them may be beneficial for health. For example, resveratrol (3,5,4'-trihydroxystilbene or 3,5,4'-stilbenetriol), which belongs to plant stilbenes and is synthesized in the skin cells of grape berries, is a well-known antioxidant reducing the risk of coronary heart disease [22; 32]. Resveratrol is also found in red wine because of skin contact during the first phase of fermentation [32]. Nevertheless, resveratrol in grape berries occurs mainly in two glycosylated forms, known as piceid or polydatin, which, however, are more hydrophilic and less bioavailable to humans than resveratrol [21]. Glycoslated forms of resveratrol can be hydrolyzed due to the activity of \(\beta\)-glucosidase, which in turn is found in some wine-related yeast strains [52; 53]. Therefore, at the end of fermentation, we determined the resveratrol concentrations in fermentation media. The next question we asked was whether adaptive evolution-mediated changes might affect yeast strains towards the production of resveratrol-enriched wines. First, we found that changes in resveratrol concentrations in the fermentation media were strain dependent. Second, adaptive evolution under KCl-induced osmotic stress had an impact on yeast strains with regard to changes in the resveratrol content in the fermented grape juice. Significant increases in resveratrol concentrations were observed, when grape juice was inoculated with the evolved derivatives of strains 1 and 2, in comparison to the corresponding ancestral strains (Figure 4). At the end of the 18% grape juice fermentation, the resveratrol concentrations were 0.41 (\(\pm\)0.09), 0.52 (\(\pm\) 0.07), 0.94(\(\pm\) 0.07), and 0.68 (\(\pm\) 0.09) mg/L for strains 1, 1_YPD, 1_KCL_a, and 1_KCI-b, respectively; and 0.28 (\(\pm\) 0.01), 0.47 (\(\pm\) 0.02), 0.76 (\(\pm\) 0.01), and 0.8 (\(\pm\) 0.03), for strains 2, 2_YPD, 2_KCL_a, and 2_KCL_b, respectively (Figure 4). Concentrations of resveratrol in 30% grape juice inoculated with strains 1, 1_YPD, 1_KCL_a, and 1_KCI-b were 0.33 (\(\pm\) 0.06), 0.60 (\(\pm\) 0.02), 0.99 (\(\pm\) 0.01), and 0.45 (\(\pm\) 0.02), respectively; and for strains 2_YPD, 2_KCL_a, and 2_KCL_b were 0.25 (\(\pm\) 0.02), 0.24 (\(\pm\) 0,01), 0.5 (\(\pm\) 0.01), and 0.24 (\(\pm\) 0.01) mg/L, respectively (Figure 4). In contrast, resveratrol concentrations were significantly decreased in the case of inoculations of grape juice with evolved derivatives of strain 3, when compared to its ancestral strain. The resveratrol concentration reached 0.93 (\(\pm\) 0.01) and 0.9 (\(\pm\) 0.01) mg/L for strain 3 growing in 18% and 30% grape juice, respectively. Decreases in its content were observed for strains 3_YPD (0.26 \(\pm\) 0.01 mg/L), 3_KCI_a (0.52 \(\pm\) 0.02 mg/L), and 3_KCI-b (0.46 \(\pm\) 0.02) growing in 18% grape juice as well as for 3_YPD (0.24 \(\pm\) 0.01 mg/L), 3_KCL_a (0.19 \(\pm\) 0.02 mg/L), and 3_KCI-b (0.38 \(\pm\) 0.02) growing in 30% grape juice (Figure 4). In general, many desirable enzymes, including \(\beta\)-glucosidase, which are responsible for modulating compounds of the grape must (by producing or releasing the preferred compounds from their precursors) and thereby affecting composition of wines, are found mainly in non-_Saccharomyces_ yeasts [1; 2]. Therefore, non-_Saccharomyces_ yeasts are often incorporated into mixed-culture fermentations; non-_Saccharomyces_ yeasts, in cooperation with _Saccharomyces_ spp., greatly improve the chemical composition and sensory profile of wines [1; 2]. To date, several strategies have been developed to obtain resveratrol-enriched wines.