## 3 Results
### Effect of the Culture Mode on Lipid Accumulation  
The experiment also compared the efficiency of microbial lipid biosynthesis in cells of _Y. lipolytica_ strain KKP 379 in batch and fed-batch media containing molasses hydrolysate and fed batch culture with post-frying rapeseed oil. Figure 2. shows changes in the lipid content of yeast cells over time. For each culture variant, the efficiency of the accumulation process reached a value of more than 30% per gram of dry biomass. Interestingly, the dynamics of microbial lipid biosynthesis for each culture varied. In the case of media in which molasses hydrolysate M1-b and M2-fb were used, the yield was highest on the first and second days of culture. For the culture in medium O1-fb with lipid carbon source on the third day of culture the maximum accumulation yield was observed. After 16 h of biomass culture in M1-b medium, the content of cellular lipids was 21% of dry cell weight, and after 24 h it was already 35%. At the same time (16 h) in M2-fb medium, the efficiency of lipid accumulation was only 8% and did not increase over the next eight hours. Probably, the medium turned out to be deficient in carbon atoms and other necessary components to cover the demand of cells in a culture environment. This type of limitation forced cells cultured in M1-b medium to accumulate lipids as an energy reservoir. In M2-fb medium, the addition of molasses hydrolysate promoted biomass growth (Figure 1b). After 48 h of cultivation, the SCO content of the cells reached a maximum (37%). A gradual decrease in the cellular lipid content of biomass was observed from 24 h of culture in M1-b medium. After 40 h, the SCO accumulation efficiency was at 26%, and after 48 h, only 10%. The observed decrease can be explained by the mobilization of cellular energy reserves in the form of lipids, due to the lack of availability of the necessary components in the substrate. In the end, after 62 h, only 2% fat per dry weight remained inside the cells. In the case of yeast culture in M2-fb medium, a decrease in cellular lipid content to 5% after reaching the maximum efficiency of the SCO accumulation process has been noted. The composition of the medium did not meet the increased biomass energy demand, which also resulted in the exploitation of cellular resources. A different mechanism was observed in O1-fb medium. At the 40 st hour for this culture variant, the SCO content of the biomass was the highest at 31.73% and remained relatively high until 90 h, reaching the efficiency maximum at 63 h (37.50%).  
The synthesis of microbial oil proceeded intensely during the first days in cultures with molasses as opposed to yeast culture in medium with post-frying rapeseed oil, where the accumulation took place in the stationary growth phase. One of the most important parameters describing the kinetics of SCOs accumulation is concentration of lipid coefficient (L) (Table 1). The highest value of this parameter was observed in 48 h of fed-batch culture with molasses (M2-fb), when L amounted to 4.01 g/L. Lipids concentration in M1-b medium without supplementation was lower, the Lmax 1.05 g/L was reached in 24 h. The value accounted for approximately 25% of the parameter calculated for the M2-fb medium. Inthe case of the O1-fb culture, the maximum amount of microbial oil that could be extracted from the medium was noted at the end of culture, L parameter reached 2.48 g/L.