Physico-chemical characterization of exomannan from Rhodotorula acheniorum MC

The batch fermentation of Rhodotorula acheniorum MC on a culture medium containing 5% sucrose, mineral salts and yeast extract at 26 degrees C for 96 h, with aeration at 0.75 v/v/m and agitation at 500 rev min(-1) resulted in the synthesis of an exopolysaccharide (6.2 g l(-1)) which formed two fractions upon precipitation. The fractions were purified to a carbohydrate content of 98.2% for fraction I and 87.3% for fraction II. Mannose was the main monosaccharide component in a 92.8% concentration in fraction I and a 90.6% concentration in Fraction II. The exopolysaccharide was thus a mannan. The gel chromatograms confirmed the chemical composition of both fractions. The molecular weight of mannan I was 310 kD, whereas that of mannan II was 249 kD. The mannan I intrinsic viscosity [eta] = 6.23 dl g(-1) was higher than that of mannan II [eta] = 2.73 dl g(-1). The water-binding capacity of the mannan samples was established within the 1.2 - 3.5 g g(-1) range. The multiplicative model [eta] = 387.22. D-r(-0.1913) T-1.095. C-1.814 describing the effect of the velocity gradient D-r, the exomannan concentration C and the temperature T on the dynamic viscosity values eta of polymer solutions was obtained.