Purification and Structure Study on Exopolysaccharides Produced by Lactobacillus casei KL1 from Tibetan Kefir

Aim: To research the pure conditions of exopolysaccharides produced by Lactobacillus casei KL1 from Tibetan Kefir, and to analyse the structure. Methods: Using Multi-level single-factor test to purify EPS by Sepharose CL-6B, purity was detected by UV scan and high performance liquid chromatogram (HPLC). EPS molecular weight and monosaccharide composition were determined by HPLC. Results: Adoption phosphate buffer gradient elution 0.02 similar to 0.10 mol/L, the velocity 0.25 mL/min, the sample concentration 1.0 mg/mL, the sample capacity 1.0 mL. Under this purification conditions, components EPSa and EPSb were obtained. The purity were 82.82% and 91.74% respectively, which were 1.4 and 1.5 times of the pre-purification. Purity Test results showed that EPSa and EPSb polysaccharide were single components, basically no nucleic acid and protein in them. Structural analysis revealed that the molecular weight of EPSa and EPSb were 4.60x10(4) Da and 2.12x10(4) Da detected by HPLC. EPSa monosaccharide components were glucose and rhamnose, and the molar ratio was 1:0.68. EPSb were composed of glucose, xylose and rhamnose, and the molar ratio was 1:0.77:0.69. Conclusion: Under the best purification conditions, the purity of exopolysaccharides can be improved. EPSa mainly composed by glucose, rhamnose component composition, EPSb mainly composed of glucose, xylose, rhamnose. All this based the foundation laid for further study of EPS's molecular structure, the structure and activity of anti-tumor function