Physicochemical characteristics and bioactivities of the exopolysaccharide and its sulphated polymer from Streptococcus thermophilus GST-6.

Abstract

Exopolysaccharide (EPS) produced by Streptococcus thermophilus GST-6 in skim milk was extracted and purified. The EPS was composed of glucose and galactose in a molar ratio of 1.80:1.03 with identical primary structure to the EPS from S. thermophilus ST1 reported previously. The purified EPS was sulphated at a sulphonation degree of 0.26±0.03, and presence of sulphate groups in the sulphated EPS (SEPS) was confirmed. Microstructural studies demonstrated a porous web with coarse surface for the EPS while the SEPS appeared as stacked flakes with relatively uniform shapes. Sulphonation of the EPS slightly decreased its degrading temperature from 234.6°C to 232.5°C. The DPPH, superoxide and hydroxyl radicals scavenging activities of the EPS were significantly (P<0.05) improved after sulphonation. The SEPS also showed stronger inhibitory activity than the EPS against Eschericia coli, Salmonella typhimurium and Staphylococcus aureus.

Keywords: Antibacterial activity; Antioxidant; Arabinose (PubChem CID: 66308); Ascorbic acid (PubChem CID: 72941984); D-Glucose (PubChem CID: 5793); Exopolysaccharide; Galactose (PubChem CID: 6036); Penicillin G (PubChem CID: 5904); Rhamnose (PubChem CID: 25310); Streptococcus thermophilus GST-6; Sulphonation; Sulphur trioxide pyridine complex (PubChem CID: 168533); Xylose (PubChem CID: 135191).