Preparation and Preliminary Characterization of Exopolysaccharides by Yeast Rhodotorula acheniorum MC

Abstract

The effects of various carbon and nitrogen sources on the synthesis of exopolysaccharides by Rhodotorula acheniorum MC were studied. The dynamic viscosity of cell-free culture broths during exopolysaccharide synthesis were measured. The highest values for the viscosity (10.14 MPa.s) and crude polysaccharide productivity (6.6 g/L) were obtained in a medium supplied with 5% sucrose. Ammonium sulfate was the most favorable nitrogen source for exopolysaccharide synthesis. The value of pH played a determinant role, and the obligatory condition for exopolysaccharide production was low (pH 1.7-2.0) during the fermentation. The chemical composition and sugar constituents of the crude exopolysaccharides were determined. Mannose was the main monosaccharide component, and its concentration was the highest (69.13%) in the crude exopolysaccharide synthesized in the medium that included 5% sucrose as a carbon source.

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“…During Rh. acheniorum MC culturing with continuous neutralization of the optimized medium with CaCO 3 , the yield of EPS synthesis was very low (Grigorova et al, 1999). Moreover, the composition of obtained EPS differed signifi cantly from that obtained in the culture without neutralization.…”

“…Among the waste carbon sources which may be a carbon substrate in the media for EPS synthesis, molasses were tested. Yeasts demonstrated a large biomass increase, however EPS synthesis, although sucrose dominates in this substrate, occurred at a very low level (Grigorova, 1999).…”

“…laurentii (Tikhomirova et al, 1998). The use of yeast EPS in combination with other polysaccharides, for example xanthan, increases the strength parameters and the viscosity value of these mixtures (Grigorova et al, 1999;Vlaev et al, 2013).…”

“…The largest amounts of exopolysaccharides were obtained in media containing 0.2% to 0.25% of ammonium sulphate (Cho et al, 2001). The use of other ammonium salts, e.g., NH 4 Cl or NH 4 NO 3 , resulted in a greater increase of biomass, but the reduction in polymers biosynthesis effi ciency was observed at the same time (Grigorova et al, 1999). The factor determining the effi ciency of EPS biosynthesis, except carbon and nitrogen source, is their molar ratio.…”

“…At the same time, it was observed that the pH of such media was not subjected to a rapid decrease. For the yeast of the Candida genus, acidity increased by 0.2 units (Gientka and Madejska, 2013), and for R. acheniorum MC it decreased by about 1.5 units (Grigorova et al, 1999). …”