## 3 Results and Discussion  
### EPS Concentration and Composition  
Many factors determine EPS production by microorganisms, including nutrients present in the culture medium--such as carbon or nitrogen [51; 52] and their concentration ratio, and also physical parameters, such as temperature, pH, or mixing speed [53; 54]. EPS are essential for proper microalgae growth in the medium as they increase their mobility, serve as a carbon source for bacteria and microfauna, and finally elicit various effects on physical and chemical parameters of the culture medium, including porosity, mechanical stability, or density [55; 56]. Besides, they preserve the structure of cell aggregates and protect them against drying out [57].  
During the culture of _Schizochrutrum_ sp. biomass under optimized initial conditions, culture medium viscosity increased from 7.15 \(\pm\) 0.91 mm\({}^{2}\)/s to 20.97 \(\pm\) 0.74 mm\({}^{2}\)/s. Its most dynamic increase, from 11.11 \(\pm\) 0.17 mm\({}^{2}\)/s to 17.77 \(\pm\) 0.16 mm\({}^{2}\)/s, was observed from the 60 h of incubation till the culture reached the stationary growth phase (Figure 1). A linear correlation was found between DCW of _Schizochrutrum_ sp. biomass, viscosity of the culture medium, and EPS concentration (Figure 2). After 120 h of incubation, DCW concentration reached 103.44 \(\pm\) 1.5 g/dm\({}^{3}\) (Figure 1). The initial EPS concentration in the culture medium was at 2.93 \(\pm\) 0.11 g/dm\({}^{3}\) and increased to 4.63 \(\pm\) 0.14 g/dm\({}^{3}\) in the 60 h of incubation. Afterward, the _Schizochrutrum_ sp. population reached the stage of the stationary growth, which determined a ramped increase in EPS concentration to 7.25 \(\pm\) 0.11 g/dm\({}^{3}\), followed by its stabilization, and its final concentration of 8.73 \(\pm\) 0.09 g/dm\({}^{3}\) after 120 h of incubation (Figure 1). Different reviews concerning microalgae EPS production have been published [58; 59]. Most of resultswere obtained in laboratory, with perfectly controlled conditions. Both the EPS productivity and the EPS concentration in the culture medium vary significantly depending on the strain studied. Nevertheless, the maximum productivity found in literature for a cyanobacteria (_Anahanea_ sp.) is 2.9 g/dm\({}^{3}\)/d, for a microcalga grown in autotrophy (_Porphyridium_ sp.) is 0.19 g/dm\({}^{3}\)/d and for a microcalga grown in heterotrophy (_Chlorella_ sp.) is 0.36 g/L/d. The average concentrations are most of the time between 0.5 and 1 g/dm\({}^{3}\)[60]. [PERSON] et al. (2005) [61] observed a lower yield of EPS production by microalgae from the _Thrustochytriacae_ family, reaching 0.3-1.1 g/dm\({}^{3}\), compared to that determined in the present study. Additionally, [PERSON] et al. (2014) [62] reported on the possibility of EPS production by the biomass _Schizochytrium_ sp. S31 and the effect of this process on the increase in the viscosity of the culture medium.  
Figure 1: Changes in _Schizochytrium_ sp. DCW concentration, medium viscosity, and EPS concentration in the culture medium during incubation.  
Figure 2: Dependence of DCW and medium viscosity on EPS fraction concentrations culture.  
Concentrations of saccharide monomers of the EPS fraction remained stable over the incubation period. The monosaccharides present in the EPS fraction included hexoses, except for xylose which is classified among pentoses. The major monosaccharide turned out to be glucose, with the concentration accounting for 60.64 \(\pm\) 1.93% mol. In contrast, the lowest concentration, reaching 2.66 \(\pm\) 1.28% mol, was found for xylose. The qualitative and quantitative composition of monomer saccharides is presented in Table 3. Similar conclusions were formulated by [PERSON] et al. (2005) [61], who additionally demonstrated that glucose, galactose, mannose, and xylose of the EPS fraction were constituents of the cell walls of the _Thraustochytriacae_ family microalgae.