## 4 Discussion
The present research showed that with an optical density of the substrate in the range of 2 to 2.2 (average OD\({}_{600}\) 2.09 \(\pm\) 0.11), the best results in the aroma production were obtained for an inoculum size of 1 mL. Larger inoculum volumes (2 mL or 5 mL) resulted in a lower concentration of aroma compound. Literature data indicate that a smaller inoculate can result in higher viable counts. [PERSON] et al. [43] analyzed the effect of inoculum size on the cultivation of soil bacteria. The authors showed that decreasing the inoculum size resulted in significant increases in the viable cell count. This may explain the much higher GDL concentrations achieved within 48 h for the lower inoculum size--0.48 \(\pm\) 0.02 g/L on the 2 nd day of reaction for an inoculum size of 0.25 mL/100 mL and two-fold less lactone for the inoculum of 5 mL/100 mL of medium. However, the kinetics of colony development did not differ for the different inoculum sizes. [PERSON] et al. [44] investigated the influence of inoculum volume on biomass, lipid content, and lipid production by _Lipomyces starkeyi_. Their analyses showed that the inoculum size had an important influence on the biomass and lipid accumulation. Experiments were conducted with different inoculum volumes ranging from 5 to 25%. The authors believe that the low inoculation concentration and the rich nutrition component in the fermentation medium were used for cell growth. A high cell concentration in the medium with the same nutrient content resulted in a lack of nutrients for metabolite synthesis. Perhaps, in our experiments, the low concentration of nutrients and ricinoleic acid was a factor contributing to the lower concentrations of GDL in the media with 2 mL and 5 mL of inoculum. Studies have shown that _Yarrougia lipolytica_ yeast, Po1d strain (a genetically modified derivative of W29 wild-type isolate, obtained at INRA France), with the selection of the appropriate lipid substrate and its concentration, also synthesizes a hexanal or \"green aldehyde\". Cultures containing linoleic acid or olive oil confirmed the substrate specificity of lipoxygenase, one of the key enzymes in the synthesis of green-note aroma compounds. Both the supernatant and the cell extract showed enzymatic activity with respect to both linoleic acid and olive oil as a lipid substrate, but the activity was much higher with linoleic acid in the medium. These results are consistent with the studies by [PERSON] et al. [45]. This team investigated the substrate specificity of the partially purified LOX (Flla) fraction of _Morchella esculent_ using free fatty acids and mono-, di-, and triacylglycerplycerols. The highest relative enzymic activity was obtained with the use of linoleic acid (100%), followed by arachidonic acid (83.3%). The results also showed that the lowest relative LOX activity of 7.7-17.8% was exhibited towards the mono-, di-, and triacylglycerplycerols. [PERSON] et al. [46] reached a similar conclusion for the catalytic activity of partially purified extracts of the yeast _Saccharomyces cerevisiae_. The level of hexanal production is also determined by the activity of hydroperoxidase, which converts the hydroperoxides of fatty acids into short-chain C\({}_{6}\)-C\({}_{9}\) forms. This enzyme is believed to be the major limiting factor in bioformation efficiency, due to the suicide inactivation phenomena and low storage and process stability. The activity of this enzyme was not determined in the conducted biotransformations. The different concentrations of linoleic acid used in the assessment of hexanal productivity by the _Yarrovia lipolytica_ Po1d strain showed that when using a higher concentration of linoleic acid, a lower level of its conversion was obtained. The determined activity of LOX was correlated with the level of hexanal production. The higher LOX activity in the cell extract observed in the culture with the higher concentration of lipid substrate corresponded to a higher aldehyde content.