## 4 Discussion  
Although research on the biosynthesis of GDL and green-note aroma compounds has been carried out for over a dozen years, the search continues for strains and the optimal \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Concentration of Linoleic**} & \multicolumn{2}{c}{**Concentration of Hexanal (mg/L)**} \\ \cline{2-3}
**Acid (g/L)** & **Cellular Extract** & **Supernatant** \\ \hline
25 & 38.68 \(\pm\) 4.87 & 8.32 \(\pm\) 2.22 \\
50 & 163.82 \(\pm\) 19.98 & 47.10 \(\pm\) 8.81 \\
100 & 189.44 \(\pm\) 29.23 & 15.40 \(\pm\) 4.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Influence of linoleic acid concentration on the level of hexanal biosynthesis by _Yarrowia lipolytica_ yeasts. Figure 5: The influence of the concentration of linoleic acid on the quantity consumed by the yeast _Yarrowia lipolytica_ and its lipoxygenase activity. reaction conditions to increase the efficiency of the process and make it more competitive on the market. The yield of synthesis of the fat-derived fragrance compounds is significantly dependent on the amount of lipid substrate in the medium. The present research on the biosynthesis of GDL showed that the higher the concentration of castor oil used in the medium, the longer the time needed to obtain the maximum concentration of lactone--from three days at an oil concentration of 10 g/L to 7 days at an oil concentration of 100 g/L. The optimal concentration of the lipid substrate in the biosynthesis of GDL is the result of the level of castor oil consumption as a source of carbon necessary for the growth of microorganisms, the intensity of multiplication of the microorganisms, the secretion of extracellular lipases, the level of hydrolysis of castor oil to tricinoleic acid, and finally the inclusion of the acid in the \(\beta\)-oxidation pathway. Similar conclusions were presented by [PERSON] et al. (2017), who also dealt with the optimization of castor oil concentrations in the context of obtaining the highest concentrations of GDL in the reaction mixture. They added 10, 30, and 50 g/L of oil to the culture media and monitored the time needed to reach the highest concentrations of GDL. The results of their experiments, as well as ours, showed that the higher the concentration of castor oil in the medium, the longer the time needed to obtain the maximum concentration of lactone. However, the team showed that the concentration of GDL in the medium was not proportional to the amount of lipid substrate used. The addition of 30 g/L castor oil resulted in about 1.84 g/L of lactone production, whereas the addition of oil at a level of 10 or 50 g/L caused the GDL synthesis to be less efficient, resulting in lower concentration of about 1.35 g/L. The decrease in lactone concentration after reaching the maximum biotransformation, observed in each medium regardless of the concentration of castor oil, was confirmed by the studies by [PERSON] et al. (2017) and [PERSON] et al. (2017). In the first case, using methyl ricinoleate in a medium at a concentration of 5 g/L, the team obtained 0.15 g of lactone per liter after 24 h of cultivation. After 40 h, the concentration of GDL decreased more than three times (to 0.05-0.06 g/L), and in the final stage of the reaction it was only 0.02 g/L (a decrease of 7.5 times). Using 10 times the amount of substrate (50 g/L of methyl ricinoleate), [PERSON] et al. (2017) achieved a maximum of about 1 g/L, with a subsequent decrease of 10 times in the next days of cultivation. Additionally, during solid-state fermentation castor seed used as the source of substrate, a decrease in the concentration of GDL in the medium was observed from the value of about 0.19 g/L obtained in the 28 th hour of culture to 0.06 g/L at 90 h of fermentation ([PERSON] et al., 2017). There are several theories explaining the reasons for this decrease in lactone concentration in the medium.