Abstract:

S2, a high molecular weight fraction of exopolysaccharides (EPS), was purified from skim milk fermented by
Lactobacillus rhamnosus KF5. The surface topography of EPS S2 in aqueous solution was observed using atomic force
microscopy (AFM). The different topographic images of EPS S2 were obtained in aqueous solutions at different concentrations of
polysaccharide. With a decrease in the concentration of polysaccharide solution, the interactions between polysaccharide molecules
were weakened. The surface topography of S2 was changed from the spherical lump, island-shape, entangled network to one/two
strand chains. At a concentration of 50 ng/mL, the polysaccharide molecules formed network structures, indicated that S2 had
branched structure. When the concentration of S2 polysaccharide was 10 ng/mL, the polysaccharides existed as flexible chains,
formed disordered random coils in water. This further proved that the random coil conformation of this molecule obtained from
light scattering and viscometry experiments, according to the theory of dilute polymer solutions.

Key words: Lactobacillus rhamnosus, exopolysaccharides, atomic force microscopy (AFM), molecular morphology