Molecular characteristics of an exopolysaccharide from Lactobacillus rhamnosus KF5 in solution

The molecular weight and chain conformation of an exopolysaccharide (EPS), S2, from Lactobacillus rhamnosus KF5 were determined by size-exclusion chromatography combined with multi-angle laser light scattering (SEC-MALLS), dynamic light scattering (DLS), viscometry and atomic force microscopy (AFM). The weight-average molecular weight (Mw), intrinsic viscosity [ƞ], radii of gyration (R(g)) and hydrodynamic radii (R(h)) were 7.5 × 10(5) Da, 2.331 dL/g, 44.3 nm and 29.4 nm, respectively. The conformational parameters were calculated from the above data according to the theory of dilute polymer solutions. The Mark-Houwink-Sakurada exponent α was found to be 0.687, and the value of the structure-sensitive parameter ρ (R(g)/R(h)) was 1.51. The results revealed that the EPS S2 existed as a random coil conformation in 0.1M NaNO3 aqueous solution. AFM further confirmed the random coil morphology of this molecule in aqueous solution. EPS S2 present extended chains (fibrous morphology), with circular side chains, dispersed in SDS solution.