Structural elucidation of the exopolysaccharide from Streptococcus thermophilus XJ53 and the effect of its molecular weight on immune activity

EPS53, a homogeneous exopolysaccharide (EPS) was isolated from Streptococcus thermophiles XJ53 fermented in skimmed milk via anion exchange column chromatography. The relative molecular weight of EPS53 was above 6.7 x 105 g/mol; its repeating structural unit of EPS53 consisted of fl-T-Galp, fl-1,3-Galf, a-1,3-Glcp and fl-1,3,6-Glcp residues in a molar ratio of 1:1:1:1, with fl-T-Galp attached to the O-6 position of fl-1,3,6-Glcp,identical to the EPS produced from S. thermophilus SFi39. EPS53-D, purified under similar conditions as EPS53 except for the deproteinization of trichloroacetic acid (TCA), had a lower molecular weight but the same repeating structural unit. The effects of EPS53 and EPS53-D on proliferation, phagocytosis and nitric oxide (NO) release of macro-phage RAW264.7 were compared. EPS53 exhibited stronger immune activity than EPS53-D, suggesting that the molecular weight might have an important effect on the activity of EPS molecules. Treatment with TCA might affect the activities of native EPSs produced by fermentation.

Automated summary

EPS53, a homogeneous exopolysaccharide (EPS), was isolated from Streptococcus thermophiles XJ53 fermented in skimmed milk and had a high molecular weight and a specific repeating structural unit. EPS53-D, obtained by deproteinization using TCA, had a lower molecular weight but the same repeating structural unit. EPS53 exhibited stronger immune activity than EPS53-D, indicating the importance of molecular weight in EPS activity. TCA treatment may affect the activities of native EPSs produced by fermentation.