Partial characterization and immunostimulatory activity of exopolysaccharides from Lactobacillus rhamnosus KF5

Lactobacillus rhamnosus KF5, a strain newly isolated from the faeces of a healthy human volunteer, has been shown to produce the exopolysaccharides (EPS) in skim milk. Two EPS fractions were separated from the fermented skim milk by removing proteins, ethanol precipitation, anion-exchange and gel permeation chromatography. Fraction S1, with a low average molecular weight of 1.36 × 104 Da, was composed of glucose, arabinose, glucosamine, galactosamine and galactose in an approximate molar ratio of 2.03:1.29:1.25:0.72:0.61. Such monosaccharide composition of the exopolysaccharide by lactic acid bacteria has not been reported so far, and S1 is likely to be an unusual type of microbial EPS. Whilst Fraction S2, with a high average molecular weight of 1.23 × 106 Da, contained rhamnose, glucose and galactose in a molar ratio of approximately 1.73:1.47:1.00. Both of EPS fractions could significantly stimulate splenocyte proliferation in vitro, indicating two EPS fractions had the potential immunomodulatory activity.