## 3 Results
### Characteristics of Microbial Oil Extracted from Y. lipolytica Yeast Cells  
It can be seen (Figure 4) that the intracellular lipids of _Y. lipolytica_ yeast are rich in monounsaturated fatty acids--they comprised close to 70% of the total of all fatty acids. Such a result is similar to the composition of fats found in cells, multiplied in a culture shaken in rich YPO medium as a control variant. The medium used in the batch and fed-batch cultures was characterised by a high carbon to nitrogen source ratio, while no nitrogen source limitation was applied in the YPO medium. The saturated fatty acid content of the microbial oils was low (6.61% to 7.44% on average), which was considered a positive characteristic from a nutritional point of view. The yeast biomass of _Y. lipolytica_ cultured in the study by [PERSON] et al. (2022) [7] in a medium with agricultural waste (i.e., rye and oat straw or bran) or industrial waste (i.e., industrial or crude glycerol) was characterized by low concentrations of total cellular lipids (8.2-20.0%, respectively), with high contents of unsaturated fatty acids (65.0-90.0% of total lipids). Among unsaturated fatty acids, MUFA monounsaturated fatty acids (57.6%), represented by oleic acid (34.0-59.2%), predominated, and polyunsaturated fatty acids (PUFA) (34.0%), represented by linoleic acid (1.9-27.0%), were present in low concentrations. The high-protein yeast biomass contained a small amount of SFA-saturated fatty acids (8.3-34.9% of total lipids) [7]. Those results were in line with our results. Based on the results (Table 5), it can be concluded that the yeast strain _Y. lipolytica_ preferentially accumulated oleic acid, an unsaturated fatty acid, and linoleic acid, an unsaturated omega-6 fatty acid, which are essential dietary components. Figure 4: Fatty acid content of microbial oils of _Y. lipolytica_ yeast cultures in bioreactor cultures in nitrogen source-limited medium and rich YPO medium without nitrogen limitation in flasks (\(p<0.05\)). [PERSON] et al. (2017) [52] analysed the fatty acid composition of triacylglycerglycerols in lipid waste carbon sources such as residual oil after a fish smoking process, waste fat after smoking cured meats, rancid butter, and rendered fat after roasting duck. Analysis of the fatty acid composition showed that duck roast fat had the highest oleic and linoleic acid content, at around 42%. Waste oil from animal products is a rich source of fatty acids and was successfully used as a rich carbon source in the culture of _Y. lipolytica_ yeast [52]. A study by [PERSON] et al. (2021) [40] compared the fatty acid profile of carbon sources, waste oil from a fish smoking process, and olive oil and analysed the biomass of yeast cultured in YPG-rich medium (with glucose) and microbial oil extracted from yeast cells cultured in limited carbon source media: MF5 (medium with waste fish oil as the carbon source), MO5 (medium with olive oil as the carbon source) and MG7 (medium with glucose as the carbon source). The fatty acid content was studied as the total fatty acid concentration (%). It was noted that the content of fatty acids, mainly oleic, linoleic, and linoleic acid, differed from our study, probably due to the different carbon sources used in the culture. For example, the oleic acid content was the highest, reaching from 66.55% to 62.73% in each culture. In a study by [PERSON], specifically in a culture where waste fish oil was used as the carbon source, the content of oleic acid was significantly lower--around 30%, which means that this carbon source is not optimal. In the case of the medium with glucose, this value was the highest, around 56%, but still lower than the value that was obtained in the current study. That paper thus indicated that yeast accumulated components from the medium (free fatty acids), which were later found in the microbial oil [40]. Oxidation of fats changes the chemical properties of molecules, leading to the deterioration of taste, smell, and food spoilage.