## 4 Discussion  
The current study aimed mainly at investigating two yeast strains collected in Livingston Island (Antarctica). The producers belonged to _Vishniacozyma victoriae_ and _Tremelomyces_ sp., respectively. However, there is not any information, to the best of our knowledge, in the available literature on examining the EPSs of these species, and therefore, our study makes a meaningful contribution to scientific knowledge. As the submerged cultivation was the most often used for the production of EPSs, we performed submerged fermentation in flasks and in a bioreactor. It provides not only higher productivity than solid-phase cultivation but also ensures precise control of physical  
Figure 4: FT-IR spectra of EPS produced by: (**A**) _Vishniacozyma victoriae_; (**B**) _Tremelomyces_ sp. factors during cultivation. In general, a uniform transformation of nutrients into biomass and EPSs when using a stirred-tank bioreactor--the most common type of bioreactor--could be obtained [6]. For example, the Antarctic yeast strain _C. laurentii_ AL65 synthesized about 3 g/L EPS under similar bioreactor conditions with 0.067 g/L/h productivity of accumulated biomass at the 96 th h by comparison with that of the current research [26]. The _V. victoriae_ strain differed from _C. laurentii_ in that it produced a higher amount of EPS, whereas the latter strain had higher biomass productivity. The differences, logically, could be explained mainly by the differences in the metabolism of yeasts. The submerged cultivation of Antarctic yeast strains had a distinct advantage of a lower pH value. The lower pH of the medium after 24 h would provide adequate protection against microbial contaminants, which has already been observed [26]. In comparison between the flask and bioreactor cultivation, the differences in the amounts of biomass and accumulated EPSs were small, but it should much prefer the bioreactor to flask fermentation due to a higher available volume and better control of the technological process. Furthermore, the use of a temperature of 22 \({}^{\circ}\)C aimed at the development of a relatively cost-effective process. In a similar way to the industrially applied yeast species, some of the promising biotechnological applications of psychrophilic yeasts have already been revealed for the synthesis of cryoprotective molecules, cold-active enzymes for use in the food industry, wastewater treatment, bioremediation, and biofuels, as well as bioactive EPSs [2]. Particularly, the biosynthesis of extracellular carbohydrate polymers is of specific interest, because our previous studies have demonstrated that Antarctic yeasts are very good producers of EPSs [9; 26]. In the current research, _V. victoriae_ and _Tremellomycetes_ sp. produced appreciable amounts of EPSs, which were much higher, by comparison to other yeast species, such as _Candida famata_ and _Candida guillimemomdii_. They were also cultivated on 5% sucrose but for 96 h in flasks [41]. Under the preferred carbon source of 5% maltose, both _Candida_ species did not produce more than 2.10-2.98 g/L EPS within 120 h of cultivation. Similarly, the probiotic yeast _Lipomyces starkeyi_ produced 4.86 g/L EPS on 2% sucrose for 30 days in flasks [42]. The carbon source is extremely important for the proper accumulation of EPSs. From a practical point of view, the production of EPSs on different by-products from the food industry containing sugars as cheap carbon sources could be examined also. In general, beet or cane molasses are industrially used to replace sucrose; however, this could lead to the production of EPSs with lower purity because of the possible physical and chemical interaction with the complex waste matrices. Not only the yield but also the structural features and molecular weight distribution of Antarctic yeast EPSs are important for the manifestation of biological activity and explanation of their interesting functional properties.