## 3 Results
### Bioreactor Scale Experiments
Despite the low biomass yield, yeast consumption of the oily substrate was at a relatively high level, similar to the M1 medium. This is another example of the diversion of the available carbon source to the needs of storage lipid accumulation, not to the energy needs associated with growth. After 63 h, the efficiency of lipid storage was lower in this medium, but still at a satisfactory level of 32.67%. When _Y. lipolytica_ yeast was cultured in M4 medium, significant changes were observed after 2 days of yeast growth. After about 40 h, dissolved oxygen consumption increased due to the increase in biomass yield, which reached 7.45 g\({}_{\rm d.m. }/\)dm\({}^{3}\) (Figure 2D). Thus, this resulted in a decrease in the lipid carbon source content of the culture medium; the final result after 88 h of culturing was a reduction to 5.33 g/dm\({}^{3}\). Molar ratios of C/P = 49.6:1 and C/N = 53.1:1 yielded 2.24 g of microbial oil per dm\({}^{3}\) of culture medium after 88 h (30.07% cell dry weight). As could be expected, the C/N ratio changed with the duration of the culture. After 24 h, when the most intensive period of cell growth was already over, the ratio decreased to C/N = 30.6:1, after the following hours it was already half (15.5:1), and at the end of the culture the molar C/N ratio was equal to 8.4:1. The marked observation to emerge from the data comparison (Figure 3) was the dominance of oleic acid (C18:1) in the total fatty acids content of the cellular oils from each medium variant. When analyzing the composition of extracted oils in the context of their potential use as nutritionally valuable products, the content of linoleic (C18:2) and linolenic acids (C18:3) should be considered. The oleic acid content of the oils ranged from 53.89% (M2) to 60.44% (M3), while the linoleic acid content ranged from 17.39% (M4) to \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Unit** & **M1** & **M2** & **M3** & **M4** \\ \hline \hline \multicolumn{1}{c}{Molar ratio in the medium [C/N/P]} & mol & 114.9/1.6/1 & 114.9/4.3/1 & 81.6/3.8/1 & 53.1/1.07 \\ Initial concentration of carbon source [S] & g/dm\({}^{3}\) & 50 & 50 & 50 & 50 \\ Time [t] & h & 63 & 88 & 63 & 88 \\ Biomass yield [X] & g\({}_{\rm d.m.}/\)dm\({}^{3}\) & 0.78 & 11.10 & 4.56 & 7.45 \\ Maximum concentration of lipids produced [L\({}_{\rm max}\)] & g/dm\({}^{3}\) & 0.37 & 2.32 & 1.49 & 2.24 \\ Conversion yield of biomass per carbon substrate [Y\({}_{\rm X/S}\)] & g\({}_{\rm d.m.}/\)g & 0.0156 & 0.2220 & 0.0912 & 0.1490 \\ Conversion yield of storage lipids per biomass formed & g/g\({}_{\rm d.m.}\) & 0.4744 & 0.2090 & 0.3267 & 0.3007 \\ Conversion yield of storage lipids per carbon substrate & g/g & 0.0074 & 0.0464 & 0.0298 & 0.0448 \\ \multicolumn{1}{c}{Volumetric rate of storage lipids production [q\({}_{\rm Ly.v}\)]} & g/dm\({}^{3}\)/h & 0.0059 & 0.0256 & 0.0236 & 0.0254 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of _Y. lipolytica_ KKP 379 yeasts strain culture in media with 5% rapeseed waste post-frying oil as a carbon source. 22.58% (M2). For cellular lipids derived from culture in M2 medium, at the same time with the lowest proportion of oleic acid, the highest contents of linoleic acid and linoleic acid (8.89%) were noted. Importantly, considering all variants of the medium, the linoleic acid was at least, 5.82%. Saturated fatty acids were also determined in each of the cellular lipid samples. The highest percentage of stearic acid was found in samples from medium M1-8.40% and M4-10.93%. Palmitic acid (C16:0) from 1.40% for medium M4 to 4.76% for M2, palmitoleic acid (C16:1): 1.06% (M1)--2.62% (M2), arachidonic acid (C20:0): 0.98% (M2)--1.55% (M4) and behenic acid (C22:0): 0.90% (M4)--2.42% (M3) were also identified. The content of myristic acid (C14:0) in the total pool of all fatty acids did not exceed 0.91%.