## 3 Results and Discussion
### Determination of Protein Content in Yeast  
The protein content in yeast cells may be related to the selenoproteins present in the yeast cell structures. Selenium in combination with proteins is easily absorbed and may constitute an effective component of our daily diet. Figure 3: Selected images of wet cell biomass of _C. utilis_ yeast from 72-h cultivation in the control (YPD) (**A**) and in the experimental media enriched with selenium ((**B**) 4 mg/L; (**C**) 20 mg/L; (**D**) 30 mg/L; (**E**) 80 mg/L; (**F**) 100 mg/L). During the initial stage of cultivation, directly after the introduction of inoculum to the experimental and control media, the total protein content in all the tested yeast cell samples of biomass ranged from 43.5% to 44.6% (Figure 4). In terms of yeast biomass from selenium-enriched experimental media (20, 30 and 60 mg/L), after 24 h of cultivation, the protein content ranged from 35.4% to 40.7%. On another day of yeast cultivation (after 48 h), when compared to _C. utilis_ cells in control YPD medium, to the protein content in the yeast cultures obtained from experimental cultures with increasing concentrations of selenium (20, 30 and 60 mg/L) decreased by 3%, 4% and 19%, respectively. The presence of 60 mg Se\({}^{4+}\)/L in the experimental medium significantly influenced the reduction of protein content as compared to the control culture. Extension of the cultivation by 72 h in the control media without the addition of selenium also significantly decreased the protein content in the biomass of yeast cell by approximately 5.7%. In experimental media supplemented with selenium at doses of 20, 30 or 60 mg/L after 72 h of cultivation, the protein content in the yeast cell biomass ranged from 33.6% to 37.7%. The results obtained after the third day of cultivation were significantly different when compared to the protein content of the initial growth phase (directly after the introduction of inoculum). However, it was reported that the differences in the protein content of _C. utilis_ yeast biomass from experimental media supplemented with selenium (20, 30 and 60 mg/L) were not significant. The reduction of the protein content in yeast cell biomass during the extension of the cultivation time could be the result of autolysis processes (effluence of lysosomal, hydrolytic enzymes). Based on the obtained results, it can be assumed that the lower protein content in yeast biomass from experimental media, when compared to the control culture, could be the result of the formation of the elemental form of selenium. This is one example of yeast detoxification processes. Metabolic changes in yeast cells due to the presence of selenium may lead to conformational changes in the polymers of the yeast cell wall. The consequence of these processes is a change in the permeability of lipid membranes [28]. According to [PERSON] [17], fodder yeast may contain approximately 46%-65% of protein. In the case of dried brewer's yeast (_Saccharomyces cerevisiae_), protein content in the biomass ranged from 40% to 50% [44]. It should be emphasized that the protein content in the yeast cell biomass is dependent on many factors: medium composition, culture conditions and individual characteristics of the strain. Figure 4: Changes in total protein content (%) in _C. utilis_ yeast cells after cultivation in the control (YPD) and in the experimental media enriched with selenium in the form of Na\({}_{2}\)SeO\({}_{3}\). \({}^{\mathrm{a-i}}\) Means with the same letter did not differ significantly (\(p<0.05\)). Test results obtained by [PERSON] et al. [45] showed that the protein content of _Yarrowia lipolytica_ A-101 yeast species cultured in crude rapeseed oil enriched with selenium (NaHSeO\({}_{3}\)), at a dose between 1 and 6 mg/L, ranging from 56.4% to 24.7%. In the case of using glucose syrup as a selenium-enriched culture medium (4 mg/L), the protein content in _Y. lipolytica_ A-101 yeast was estimated at approximately 45%. According to [PERSON] et al.