## 3 Results
### Fatty Acids Composition of Cellular Lipids from Y. lipolytica Cultures  
To compare the fatty acid composition of cellular lipids obtained by de novo accumulation in molasses media and by the ex novo pathway in culture with post-frying waste, oil samples from M1-b, M2-fb and O1-fb (Table 2) cultures were analyzed. For both microbial oils accumulated in biomass cultured in molasses media and in cultures with post-frying oil, the fatty acid with the dominant proportion was oleic acid (C18:1). After 62 h, in oil samples from M1-b culture, the C18:1 content was 52.66%, in M2-fb--44.43%, and in O1-fb--61.82%. Linoleic acid (C18:2) was another fatty acid with a significant proportion. The highest percentage of C18:2 was observed in SCO from the M2-fb culture (30.75%). In the oil sample from the M1-b culture as well as the M2-fb medium, linolenic acid (18:3) from the omega-3 fatty acids was present, 7.68% and 6.48%, respectively. Saturated fatty acids such as palmitic acid (C16:0) and stearic acid (C18:0) were also determined in each of the oil samples.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Unit** & **M1-b** & **M2-fb** & **O1-fb** \\ \hline Initial concentration of carbon source & g/L & 50 & 50 & 50 \\ \hline Time (t) & h & 62 & 62 & 91 \\ \hline Biomass yield (X) & g\({}_{\mathrm{DCW}}\)/L & 6.00 & 11.82 & 8.08 \\ \hline Conversion biomass yield per carbon & & & & \\ substrate (Y\({}_{X/S}\)) & g\({}_{\mathrm{DCW}}\)/g & 0.1200 & 0.2364 & 0.1616 \\ \hline \multirow{6}{*}{Concentration of lipids produced (L)} & \multirow{2}{*}{g/L} & 16 h & 0.6090 & 0.0480 & - \\ \cline{3-5}  & & 24 h & 1.0500 & 0.2590 & - \\ \cline{3-5}  & & 40 h & 0.9100 & 1.3585 & 0.6600 \\ \cline{3-5}  & & 48 h & 0.5100 & 4.0108 & 1.4454 \\ \cline{3-5}  & & 62 h & 0.1200 & 0.5925 & 2.1900 \\ \cline{3-5}  & & 72 h & - & - & 2.2762 \\ \cline{3-5}  & & 90 h & - & - & 2.4846 \\ \hline \end{tabular}
\end{table}
Table 1: Parameters of _Y. lipolytica_ KKP 379 yeasts strain culture in media M1-b, M2-fb and O1-fb.  
Figure 2: Cellular lipid content of _Y. lipolytica_ KKP 379 during batch culture in medium M1-b and fed-batch cultures in medium O1-fb and M2-fb.  
For microbial oil extracted from biomass cultured in O1-fb medium changes in fatty acid composition were observed after 40, 48, 62, 72 and 90 h. The cellular oil extracted from the biomass after 90 h of culture containing the most C18:1 acid (66.94%) was at the same time characterized by the lowest proportion of C18:2 acid from the omega-6 group (14.41%). Considering the change in the content of C18:2 in the total fatty acids profile of microbial oils from successive O1-fb culture stages, its percentage decreased with the time of cultivation. The highest amount of C18:2 was noted on the second day of the culture stage (18.88%).  
Oil samples from O1-fb cultures were characterized by a small proportion of C18:3 acid. Its content after 40 h was 4.20%. In the following hours its content decreased, and at the end of the culture it was only 0.72% of all fatty acids. Microbial oils from O1-fb culture were more differentiated in fatty acid composition. In contrast to cellular lipid samples from strain cultures in molasses media, arachidonic acid (C20:0) and behenic acid (C22:0) was detected in SCOs from O1-fb cultures.