# Application of Extracellular Polymeric Substances during Cultivation of Microalgae Biomass
## 3 Results and Discussion
Based on the results of the EPS content and composition and sedimentation properties of _T. subcordiformis_  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **Variant of** & **Protein Content** & **Sugar Content** & \multicolumn{4}{c}{**Carbohydrates**} \\  & **Experiment** & **(mg/g VS)** & **(mg/g VS)** & **Glucose** & **Mannose** & **Rhamnose** & **Galactose** \\  & & **(mg/g VS)** & **(mg/g VS)** & **(mg/g VS)** & **(mg/g VS)** & **(mg/g VS)** \\ \hline \multirow{4}{*}{_Tetraselmis_ _subcordiformis_} & C & 27.4 \(\pm\) 6.7 & 21.5 \(\pm\) 4.5 & 15.2 \(\pm\) 5.4 & - & - & 1.3 \(\pm\) 0.5 \\  & V1 & 28 \(\pm\) 4.8 & 25.3 \(\pm\) 5.6 & 21 \(\pm\) 1.1 & - & - & 1.9 \(\pm\) 0.4 \\  & V2 & 27.9 \(\pm\) 3.5 & 32 \(\pm\) 3 & 24.3 \(\pm\) 2.7 & - & - & 1.9 \(\pm\) 1.5 \\  & V3 & 28.3 \(\pm\) 9.2 & 41 \(\pm\) 5 & 22.5 \(\pm\) 3.2 & - & - & 2.1 \(\pm\) 0.8 \\ \hline \multirow{4}{*}{_Chlorella_ sp.} & C & 32.9 \(\pm\) 4.7 & 41.1 \(\pm\) 4 & 17.8 \(\pm\) 3.2 & 12.9 \(\pm\) 5.2 & - & 1.1 \(\pm\) 0.2 \\  & V1 & 33.1 \(\pm\) 8.8 & 50.3 \(\pm\) 8.2 & 23.8 \(\pm\) 2.5 & 19.4 \(\pm\) 3.8 & - & 1.7 \(\pm\) 0.1 \\  & V2 & 33.7 \(\pm\) 5.3 & 53.7 \(\pm\) 9.1 & 24.1 \(\pm\) 5.3 & 20.1 \(\pm\) 2.7 & - & 1.7 \(\pm\) 0.5 \\  & V3 & 35.6 \(\pm\) 4.9 & 56.3 \(\pm\) 7.7 & 23.9 \(\pm\) 4.5 & 21.1 \(\pm\) 3.2 & - & 2.2 \(\pm\) 1.1 \\ \hline \multirow{4}{*}{_Arthrospira_ _platensis_} & C & 45 \(\pm\) 10.3 & 37.8 \(\pm\) 6.4 & 11.4 \(\pm\) 1.2 & - & 25.1 \(\pm\) 3.2 & 10.9 \(\pm\) 1.4 \\  & V1 & 59.1 \(\pm\) 9.1 & 42.8 \(\pm\) 9.8 & 10.5 \(\pm\) 5 & - & 26.7 \(\pm\) 1.9 & 8.6 \(\pm\) 3.1 \\ \cline{1-1}  & V2 & 57 \(\pm\) 13.2 & 45.2 \(\pm\) 8.1 & 11.9 \(\pm\) 2.1 & - & 29.6 \(\pm\) 0.5 & 9.1 \(\pm\) 4 \\ \cline{1-1}  & V3 & 60.1 \and _Chlorella_ sp., it might be concluded that similar flocculants induce the production of different exopolsaccharides with different properties. The applied strategy and flocculant did not improve the sedimentation properties of _Chlorella_ sp. Similar observations were made by [37]. The authors tested the settling properties of two species of microalgae, namely _Scenedesmus_ sp. and _Chlorella vulgaris_, with and without cultures of the bacterium _Burkholderia cepacia_ and bacterial exudates. _C. vulgaris_' settling properties were not improved by applying flocculants at any growth stage. In contrast, glutathione significantly increased the EPS content in _Chlorella pyrenoidosa_ and the settling properties above 72% [38]. The biomass of _Chlorella vulgaris_ could even have 94% harvesting efficiency when the culture was contaminated with bacteria [39]. The stress conditions that could include bacteria presence, nitrogen depletion, etc., could induce the autoflocculation of microalgal cells and improve sedimentation [40]. The stress and autoflocculation might also be the results of changes in cell surface properties. It was proved that the cell surface charge of _Chlorella_ sp. is different during the growth phases of biomass. These changes are related to the formation of a protective layer at the cell wall during late cultivation stages [41]. However, in the present study, the EPS added to the microalgae culture probably did not cause stress conditions for the cells of _Chlorella_ sp. and was only a good source of external carbon for changing the metabolism for mixotrophic cultivation. In the EPS extracted from _A. platensis_, the sugar content increased. The carbohydrates detected in all variants of experiments were glucose, rhamnose, and galactose. The addition of EPS at the end of the growth phase (V2 and V3) only increased the content of rhamnose in the EPS extracted from _A. platensis_. In the comparison of the mixotrophic and heterotrophic cultivation of _A. platensis_ with whey as an external carbon source, the growth rate and protein and lipid contents were higher under heterotrophic cultivation; however, chlorophyll-a and total carbohydrates were higher in the mixotrophic culture [30]. In the present study, the cultures of _A.