鼠李糖乳杆菌胞外多糖S2的原子力显微镜观察

胞外多糖S2是从鼠李糖乳杆菌（Lactobacillus rhamnosus）KF5的发酵乳中分离纯化得到的高分子质量组分。采用原子力显微镜（atomic force microscopy，AFM）对胞外多糖S2在水溶液中的表观形貌进行观察。结果表明：不同质量浓度的胞外多糖S2经AFM成像，得到了不同形貌多糖分子聚集行为的图像。随着胞外多糖S2质量浓度的降低，多糖分子之间的作用力减弱，外貌发生从膜状、岛屿状、网格状到单链/双链结构的变化。当胞外多糖S2质量浓度为50 ng/mL时，多糖分子间形成网状结构，说明胞外多糖S2具有多分支的化学结构。当胞外多糖S2质量浓度为10 ng/mL时，多糖分子在水溶液中呈柔性链，形成无规卷曲的构象，进一步验证了由高分子稀溶液理论推断的无规卷曲构象的结论。

Observation of Exopolysaccharide S2 from Lactobacillus rhamnosus KF5 Using Atomic Force Microscopy

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.