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 °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 [η]=6.23 dl g−1 was higher than that of mannan II [η]=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 [η]=387.22. D r −0.1913 . T−1.095. C1.814 describing the effect of the velocity gradient Dr, the exomannan concentration C and the temperature T on the dynamic viscosity values η of polymer solutions was obtained.