## 2 Results and Discussion  
### Selenium Content in Yeast Biomass  
Research conducted on the processes of element accumulation by yeast cells is of significance for the production of functional foods enriched with microelements. Among the additives used in nutrition, dried yeasts can constitute a rich source of selenium. It is possible to enrich food products and feeds with selenium, which constitutes another source of the element in the nutrition of humans and farm animals. The cell biomass of _Candida utils_ ATCC 9950 yeasts obtained after culture on media containing industrial waste products (potato juice, 5% glycerol) constituted a natural adsorbent utilized in the process of selenium binding from aqueous solutions. The total selenium content after 24 h culture determined in _C. utilis_ yeast cell biomass was 629 \(\upmu\)g\(\cdot\)g\({}^{-1}\). Extraction efficiency was approximately 67%. The total selenium content was determined for the later speciation identification of selenium compounds found in _C. utilis_ feed yeasts (ATCC 9950). In the chromatographic conditions conducted, the study results obtained demonstrated the presence of clear peaks and a good separation efficiency throughout the process, which lasted 20 min (Figure 1). As can be seen from literature data, yeasts are capable of binding large amounts of selenium, up to 6000 \(\upmu\)g\(\cdot\)g\({}^{-1}\)[13]. The study of [PERSON] et al. [9] demonstrated that Torula yeast biomass was capable of accumulating selenium in the range of 3600 to 4000 \(\upmu\)g\(\cdot\)g\({}^{-1}\) and the selenomethine content obtained in these yeasts ranged from 270 to 440 \(\upmu\)g\(\cdot\)g\({}^{-1}\). These results are comparable to those published by [PERSON] et al. [10], which indicated that _C. utilis_ ATCC 9950 grown in a bioreactor on a YPD medium enriched with selenium at a dose of 20 mg\(\cdot\)L\({}^{-1}\) are capable of binding 427.5 \(\upmu\)g\(\cdot\)g\({}^{-1}\) after 24 h culture. After the second day of culture, the selenium content in the biomass was 1804 \(\upmu\)g\(\cdot\)g\({}^{-1}\). The experiments performed by [PERSON] et al. [14] demonstrated that _Saccharomyces cerevisiae_ baker's yeast grown for 72 h on media supplemented with sodium(IV) hydroselenite (12 mg\(\cdot\)L\({}^{-1}\)) only bound 203 \(\upmu\)g Se\({}^{4+}\cdot\)g\({}^{-1}\). The above relationships, which present the capacity of yeasts to bind a large amount of selenium, were confirmed in the study of [PERSON] et al. [15]. Treating yeast cells with a pulsating electric field  
Figure 1: Chromatogram obtained for a standard mixture with 500 ppb concentration Se: 1: methyl-Se-cysteine, \(\mathrm{t_{R}}\) = 2.6 min, 2: Se-methionine, \(\mathrm{t_{R}}\) = 4.2 min, 3: Se(IV), \(\mathrm{t_{R}}\) = 7.1 min, 4: glutamyl-Se-methylcysteine, \(\mathrm{t_{R}}\) = 11.3 min, 5: Se(VI), \(\mathrm{t_{R}}\) = 13.3 min. (PEF) with an electric field intensity of 3.0 kV\(\cdot\)cm\({}^{-1}\) led to an increase in selenium (Se\({}^{4+}\)) content in the cellular biomass of _Saccharomyces cerevisiae_ 11 B\({}_{1}\) yeasts up to a value of 42.80 mg\(\cdot\)g\({}^{-1}\). Figure 2A,B presents the chromatograms obtained for an extract from _C. utilis_ ATCC 9950 yeast prior to and after sample concentration (sample concentration was performed to analyze individual fractions with subsequent usage of the UHPLC-ESI-Orbitrap-MS system). Chromatographic signals obtained by using the HPLC ICP-MS coupled system (Figure 2A,B) for _C. utilis_ ATCC 9950 biomass extract had a higher intensity for a peak with a retention time of 2.2 min corresponding to an unknown compound. This was likely a SeMet form occurring in an oxidized form (SeMetO) [16; 17]. An additional peak, with a retention time of 2.6 min, corresponds to Se-methyl-SeCys; however, its presence should have been confirmed using other mass spectrometry techniques, such as ESI-QqQ-MS-MS, and/or ESI-Orbitrap-MS. Figure 2A,B presents a signal from Se-methionine with a retention time of 4.2 min and several unidentified selenium forms.