Dilute and semi-dilute solution properties of an exopolysaccharide from Escherichia coli strain S61

The solution properties of colanic acid, an exopolysaccharide slime isolated from Escherichia coli strain 61, have been investigated. Previous chemical analysis (Sutherland, 1969) had shown that this polysaccharide contained glucose, galactose and glucuronic acid, in addition to acetate and pyruvate. Three batches (S61-1, S61-2 and S61-3) of colanic acid were used for rheological measurements. The intrinsic viscosity of S61-1, S61-2 and S61-3 were found to be 20.8±0.4 dl/g (0.2 M NaCl), 22.7±0.6 dl/g (0.2 M NaCl) and 21.1±0.3 dl/g (0.2 M CaCl2) respectively, which indicates that the colanic acid is of high molecular weight. The semi-dilute solution characteristics, investigated by steady shear and dynamic rheometry, suggest that colanic acid acts as a well behaved polymer entanglement system. The viscosity-polymer concentration relationship of colanic acid shows no significant ‘critical’ breakpoint concentration on passing from a dilute to a semi-dilute solution. Instead, there seems to be a gradual change in slope from the first regime, ∼1, to the second regime, ∼3.6.