## 3 Results
### Recovery of Gamma-Decalactone from Bittransformation Media by Hydrodistillation  
Attempts to separate GDL from biotransformation media were also carried out via hydrodistillation (HD). Castor oil biotransformation reactions (10 g/L) were performed with _Yarrowia_ yeast for eight days. Each day the reaction mixture from the flask was distilled, and the GDL concentration in the distillate was compared with the values obtained from the direct liquid-liquid extraction with diethyl ether. The data presented in Figure 1 show that the use of hydrodistillation allowed the separation of GDL from the media, regardless of the level of the substrate conversion, and the use of this method is associated with a partial loss of the lactone. The concentration of the compound in the distillates on each sampling day was lower than in extracts, and the difference in determinations with the lactone content above 0.5 g/L ranged from 12.8% to 22% (from 0.25 g/L to 0.63 g/L). In the range of lower lactone concentrations, the differences in the distillates compared to the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Extraction Solvent Type** & \
\begin{tabular}{c} **Solvent Volume per Sample** \\ **Volume (mL/mL)** \\ \end{tabular} &
\begin{tabular}{c} **Average Percent Recovery** \\ **and RSD \({}^{*}\) Values (\%)** \\ \end{tabular} \\ \hline Hexane & 1:2 & 84.3 (4.1) \\  & 1:1 & 92.8 (2.1) \\ \hline Heptane & 1:2 & 72.1 (3.7) \\  & 1:1 & 87.0 (2.7) \\ \hline Diethyl ether & 1:2 & 87.9 (2.1) \\  & 1:1 & 99.9 (1.8) \\ \hline Chloroform & 1:2 & 85.5 (3.3) \\  & 1:1 & 98.8 (1.3) \\ \hline Dichloromethane & 1:2 & 89.4 (4.4) \\  & 1:1 & 101.1 (2.5) \\ \hline \hline \end{tabular} \({}^{*}\) RSD—Relative Standard Deviation.  
\end{table} 
Table 2: Gamma-decalactone recovery degree from model solutions by different solvents. extracts were as high as 73%. However, this may be due to an error of sample determination as it is difficult to separate the lactone effectively at its low concentrations. However, taking into account the purity of the product in the distillate (about 88% \(\pm\) 3.4%), this process seems to be more advantageous than liquid-liquid extraction. While conducting research on GDL hydrodistillation, the influence of the pH of the reaction mixture on the level of GDL concentration in the distillate was analyzed. On the seventh day of cultivation, when the lactone concentration was at its maximum (Figure 1) or close to it, the medium was acidified or alkalized to the pH at the levels of 1, 3, 5, or 7, and then the GDL was separated with the usage of hydrodistillation and determined chromatographically. The results of GDL concentration in the media before and after pH modifications as well as in the distillate and distillation residue are summarized in Table 3.  
The presented data clearly show that the pH of the medium has a significant influence on the concentration of GDL in the biotransformation medium, and thus, finally, in the distillate. With the decrease in the pH (acidification of the medium), the concentration of the lactone in the post-reaction mixture increased. The highest content of the lactone was recorded at the pH of 3 or 1. Acidification contributed to an increase in the concentration of the GDL in the extracted samples by approximately 33.3% and 8.8% (from 2.76 \(\pm\) 0.09 to 3.68 \(\pm\) 0.26 for pH 3, and from 2.97 \(\pm\) 0.21 to 3.25 \(\pm\) 0.15 for pH = 1). This is due to the spontaneous cyclization of 4-hydroxydecanoic acid into the neutral lactone form. However, this reaction is not total and some of the acid is not transformed into GDL. Figure 1: Comparison of gamma-decalactone concentration in biotransformation medium by extraction and hydrodistillation methods.