The EPS produced by S. thermophilus in skim milk was extracted and sulphonated.
The EPS was composed of hexasaccharide repeating unit of glucose and galactose.
More uniform microstructure was obtained after sulphonation of the EPS.
Sulphonation lowered the degradation temperature of the EPS.
Antioxidant and antibacterial activities increased after sulphonation of the EPS.