## 3 Results
### The Analysis of the Conditions for Gamma-Decalactone Biosynthesis
#### 3.1.4 Effect of the Emulsification of the Medium on Gamma-Decalactone Production  
Another element of the present research was to analyze the influence of medium emulsification on the GDL production. It is believed that the contact surface of fat droplets with cells of multiplied organisms and the contact surface between two liquid phases may be a factor affecting the degradation of the hydrophobic substrate, and thus cell growth and aroma production. Without emulsification, the lipid and water phases clearly separate, which causes problems when taking a reliable sample [35]. Attention was paid to the level of multiplication of yeast cells and the lipolytic activity they exhibited. Moreover, the conversion yield of GDL per biomass formed was compared and the specific rate of GDL production was calculated (Table 1). The data presented in Table 1 show that the emulsification of the medium allowed higher biotransformation yields to be obtained. On both the 3 rd and 7 th days of the reaction, the amount of GDL produced in relation to the dry weight of the cells in the emulsified media was twice as high as that in the nonemulsified medium. The \(Y_{L/X}\) parameter was the highest on the 7 th day of the reaction (0.283 g/gd.w), and on that day the highest concentration of lactone was recorded, reaching the level of 5.25 \(\pm\) 0.10 g/L. This value was about 2 g higher than in the nonemulsified medium. It may have been related to the high extracellular lipolytic activity of _Yarrovia_ yeast in this medium observed on the 3 rd day of cultivation (1.46 \(\pm\) 0.18 U/mL). The activity of lipases is important for the hydrolysis of castor oil present in the medium in order to release ribonucleic acid, the precursor of GDL. The yield of biomass shows that the emulsification of the medium contributes to slower and less intensive multiplication of cells. It is assumed that in nonemulsified media, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Culture** \\ **Time** \\ \end{tabular} } & \multirow{2}{*}{**Medium**} & \multirow{2}{*}{\begin{tabular}{c} **Concentration** \\ **of GDL \(L\) **(g/L)** \\ \end{tabular} } & \begin{tabular}{c} **Lipolytic** \\ **Activity** \\ **(U/mL)** \\ \end{tabular} & \begin{tabular}{c} **Biomass** \\ **Yield X** \\ **(gd.w/L)** \\ \end{tabular} & \begin{tabular}{c} **Conversion Yield of** \\ **GDL Per Biomass** \\ **Formed Y\({}_{LX}\) (g/gd.w.)** \\ \end{tabular} & \begin{tabular}{c} **Specific Rate of** \\ **GDL Production** \\ \(q_{L}\) (g/gd.w/h)** \\ \end{tabular} \\ \hline \multirow{2}{*}{3 rd day} & non- & \multirow{2}{*}{\
\begin{tabular}{c} 2.02 \(\pm\) 0.06 \({}^{\text{a}}\) \\ emulsified \\ 1.66 \(\pm\) 0.08 \({}^{\text{a}}\) \\ \end{tabular} } & 0.13 \(\pm\) 0.02 \({}^{\text{a}}\) & 21.85 \(\pm\) 2.99 \({}^{\text{c}}\) & 0.092 \({}^{\text{a}}\) & 0.0013 \({}^{\text{b}}\) \\  & 1.46 \(\pm\) 0.18 \({}^{\text{c}}\) & 8.48 \(\pm\) 0.87 \({}^{\text{a}}\) & 0.196 \({}^{\text{c}}\) & 0.0027 \({}^{\text{d}}\) \\ \hline \multirow{2}{*}{7 th day} & non- & \multirow{2}{*}{
\begin{tabular}{c} 3.21 \(\pm\) 0.14 \({}^{\text{b}}\) \\ emulsified \\ \end{tabular} } & 3.21 \(\pm\) 0.14 \({}^{\text{b}}\) & 0.23 \(\pm\) 0.04 \({}^{\text{b}}\) & 22.03 \(\pm\) 3.08 \({}^{\text{c}}\) & 0.146 \({}^{\text{b}}\) & 0.0009 \({}^{\text{a}}\) \\  & 5.25 \(\pm\) 0.10 \({}^{\text{c}}\) & 0.26 \(\pm\) 0.05 \({}^{\text{b}}\) & 18.58 \(\pm\) 1.55 \({}^{\text{b}}\) & 0.283 \({}^{\text{d}}\) & 0.0017 \({}^{\text{c}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Effect of the emulsification of the medium on growth and catalytic activity of the yeast _Yarrovia lipolytica_. Figure 3: Effect of surfactant addition (5 g/L) on biotransformation of ribonucleic acid into GDL by yeast _Yarrovia lipolytica_. yeast cells reached the stationary phase of growth much earlier (on the 3 rd day of the reaction), because the difference in the biomass yield between the 3 rd and 7 th days was statistically insignificant.