## 2 Results
### Effect of Plasma-Treated Water on the Synthesis of Gamma-Decalatone and other Volatile Metabolites  
The yeast _Y. lipolytica_, successfully synthesized the fragrance compound--gamma-decalactone (Figure 3--solid lines), regardless of the variant of plasma water used for their culture. The highest GDL concentration was achieved in the Nantes plasma water, and it amounted to approximately 4.81 \(\pm\) 0.51 g/L at 144 h of culture. Lower concentrations of about 3.11 \(\pm\) 0.03 g/L and 3.51 \(\pm\) 0.01 g/L were obtained for the media PWTA and PWTN, respectively. In each nanowater-based media, the concentration of the peach-aroma compound was higher relative to the control culture, and this difference ranged from approx. 0.36 to 2.05 g/L, which as a percentage represented from 13% (for the PWTA medium) to 74% (for Nantes PW medium). Irrespective of the variant of culture carried out, the curves of the time-varying GDL concentration peaked at the 5 th (control culture) or 6 th (plasma water-based media) day of cultivation. In order to compare the biotransformation yield of yeasts grown in plasma water-based media in the presence of individual gases, kinetic parameters such as the GDL accumulation efficiency in relation to biomass yield and substrate, as well as the average specific and volumetric accumulation rate of this compound, were also compared (Table 2). In relation to biomass yield, the GDL accumulation efficiency for all plasma water types was lower compared to the control medium. The lowest value of 0.294 g/gd.w. was achieved when Nantes plasma water was used in the medium. This was approximately 18% lower than the control medium. The parameter of GDL accumulation calculated relative to the substrate showed an opposite trend. The medium with singlet oxygen-enhanced water, for which the YGDL/S parameter was 0.048, stood out as statistically significant, while the medium PWTN or PWTA showed a lower value of this parameter by approximately 35%. Comparing the average volumetric rate of GDL accumulation (qLVGDL) in the different media, it can be seen that between the most efficient (Nantes PW) and the least efficient biotransformation (control medium), the volumetric rate was about 1.4 times lower. In the case of the average rate of specific accumulation of GDL related to the yeast cell dry matter yield (qLGDL), the specific production rate statistically differed by about 0.7 times in favor of the control medium. The analysis and identification of volatile compounds produced in the individual biotransformation medium was performed using the HS-SPME-GC-MS technique. During the analysis, special attention was focused on the group of lactones. Twenty-nine volatile compounds were detected in the samples from the four different biotransformation media with _Y. lipolytica_ after 72 h of cultivation (Table 3). Regardless of the type of medium (based on distilled or plasma water), higher alcohols (3-methyl-butan-1-ol, _n_-heptanol, oct-1-en-3-ol, 2-phenylethanol), carbonyl compounds (aldehydes: hexanal, heptanal, benzaldehyde, phenylacetaldehyde and one ketone: 2-octanone), fatty acids (2-methyl-butanoic acid, 3-methyl \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{4}{c}{**Type of Medium**} \\ \cline{2-5}  & **Control Medium** & **PWTN** & **PWTA** & **Nantes PW** \\ \hline YGDL/Xmax (g/gd.w.) & 0.359 a & 0.334 b & 0.358 a & 0.294 c \\ \hline YGDL/S (g/g) & 0.028 a & 0,031 a & 0.031 a & 0.048 b \\ \hline qLVGDL (g/L/h) & 0.023 a & 0.029 b & 0.026 a & 0.033 c \\ \hline qLGDL (g/gd.w./h) & 0.0030 a & 0.0028 b & 0.0030 a & 0.0020 c \\ \hline \hline \end{tabular} Mean values followed by the same letter are not significantly different according to HSD Tukey (\(p\leq 0.05\)). YGDL/Xmax—conversion of DGL per biomass yield. YGDL/S—conversion of GDL per carbon substrate. qLVGDL—volumetric rate of gamma-decalactone production. qLGDL—specific rate of gamma-decalactone production.  
\end{table} 
Table 2: Kinetic parameters of GDL biosynthesis by _Y.