Chemical characterization and biological effect of exopolysaccharides synthesized by Antarctic yeasts Cystobasidium ongulense AL101 and Leucosporidium yakuticum AL102 on murine innate immune cells

The current study aimed to investigate exopolysaccharides (EPSs) produced by two Antarctic yeasts isolated from soil and penguin feathers samples collected on Livingston Island (Antarctica). The strains were identified as belonging to the species Leucosporidium yakuticum (LY) and Cystobasidium ongulense (CO) based on molecular genetic analysis. The EPS production was investigated using submerged cultivation. Different chemical, chromatographic, and spectral analyses were employed to characterize EPSs. LY accumulated 5.5 g/L biomass and 4.0 g/L EPS after 120 h of cultivation, while CO synthesized 2.1 g/L EPS at the end of cultivation, and the biomass amount reached 5.5 g/L. LY-EPS was characterized by a higher total carbohydrate content (80%) and a lower protein content (18%) by comparison with CO-EPS (62%, 30%). The LY-EPS mainly consisted of mannose (90 mol%), whereas CO-EPS had also glucose, galactose, and small amounts of uronic acids (8-5 mol%). Spectral analyses (FT-IR and 1D, 2D NMR) revealed that LY-EPS comprised a typical β-(1 → 4)-mannan. Branched (hetero)mannan, together with β/α-glucans constituted the majority of CO-EPS. Unlike LY-EPS, which had a high percentage of high molecular weight populations, CO-EPS displayed a large quantity of lower molecular weight fractions and a higher degree of heterogeneity. LY-EPS (100 ng/mL) elevated significantly interferon gamma (IFN-γ) production in splenic murine macrophages and natural killer (NK) cells. The results indicated that newly identified EPSs might affect IFN-γ signaling and in turn, might enhance anti-infectious responses. The data obtained also revealed the potential of EPSs and yeasts for practical application in biochemical engineering and biotechnology.

Stress response and characterization of oil-in-water emulsions stabilized with Kluyveromyces marxianus mannoprotein

This study was intended to investigate physico-chemical, rheological, and emulsifying properties of oil-in-water emulsions prepared from the Kluyveromyces marxianus mannoprotein (KMM). Also, the stress-response function of the KMM emulsions was compared with that of the whey protein concentrate (WPC) emulsions in terms of zeta potential, size, and rheology. The stress experiments were conducted at different pH (3 to 9), ionic composition (0 to 500 mM NaCl), and temperatures (30 to 90 °C). The extracted KMM with a molecular weight of 107.2 kDa had 28.8% proteins and 68.22% carbohydrates. With increasing the KMM concentration to 1.5% (w/w), the zeta potential, droplet size, and apparent viscosity of the emulsions reached -35 mV, ∼1 μ, and ∼9 mPa·s, respectively. After applying pH, ionic composition, and temperature, the KMM emulsions were more stable than the WPC emulsions. In conclusion, KMM can be used as a bioemulsifier and be more effective in stabilizing emulsions than WPC. PRACTICAL APPLICATION: Yeasts are a rich source of natural materials. In this study, we extracted mannoproteins from the yeast cell wall and evaluated their functional properties to be used as an emulsifier in oil-in-water emulsions. The results of this study confirm that the yeast-derived mannoproteins are good at stabilizing these emulsions either in the presence or absence of different environmental conditions.