Effect of structural modification of exopolysaccharide, methylan on the rheological property of its solution

Abstract

In order to investigate the effect of change in acidic component of the polysaccharide, Methylan produced from Methylobacterium organophilum on the rheological property, identification of chemical composition of polysaccharide, determination of sugar and nonsugar components, noncarbohydrate components, molecular weight, effect of culture conditions, such as culture temperature and addition of pyruvate on change in acidic component were carried out. Methylan was found to have a high molecular weight about 4-5*$10^6$ dalton, and contained 80.4%(w/w) of carbohydrate but no polyhydroxybutyrate. Other organic constituents were consisted of protein, pyruvic acid, uronic acid, and acetic acid. Based on the chemical analyses of polysaccharide by TLC and gas chromatographic methods, it was found that the polysaccharide was consisted of glucose, galactose, and mannose with an approximate molar ratio of 2:3:2. The pyruvate content in polysaccharide increased with increase in pyruvate concentration of culture media, and culture temperature also affected pyruvate content and rheological property. The acidic component, pyruvate in polysaccharide was depyruvylated by acid-hydrolysis and change in pyruvate content also affected intrinsic viscosity and steady ahear viscosity of polysaccharide solution. Chemical modifications such as reduction of uronic acid to its corresponding neutral sugar also affected rheological property of polysaccharide solution. The enzymatic modification of polyusaccharide by treatment with glycolytic hydrolase suggested that polysaccharide probably contained β 1→4, α 1→4 and α 1→6 linkage. The polysaccharide adsorbed non-selectively metal ions, 24% for copper, 18% lead per weight basis.