Chemical components, molecular characterization and rheological properties of exopolysaccharides produced by Streptococcus thermophilus strains

The exopolysaccharide (EPS) from Streptococcus thermophilus was typically viscous. However, the relationship between viscosity and molecular parameters of EPS has not been studied systematically. This study selected five S. thermophilus with low genome sequence identity for EPS production (NEPS1, NEPS3, NEPS4, NEPS7 and NEPS12), and aimed to investigate the chemical components, molecular and rheological properties of EPSs, in order to gain insight into their intrinsic relationships. The monosaccharide composition of EPSs was mainly identified as galactosamine, galactose, glucose and mannose with different proportions. Their molecular weights were in the range of 6.04 × 10 4 –7.19 × 10 5 Da. EPSs exhibited different conformations in solution. NEPS3 and NEPS4 were rigid rods, while NEPS1 and NEPS7 were random coils. NEPS12 tended to be spherical. The apparent viscosity of EPS solutions was in the order of NEPS12 > NEPS1 > NEPS7 > NEPS4 > NEPS3. The correlation analysis demonstrated that viscosity was positively correlated with yield, molecular weight and galactose content of EPSs, while negatively correlated with the conformation parameter α . These findings are of significance for understanding the relationship between molecular characteristics and the viscosity of EPS. • EPSs produced by five selected strains of S. thermophilus were separated. • EPSs were mainly composed of galactosamine, galactose, glucose and mannose. • The molecular weights of EPSs were 60.4–719 kDa with different conformations. • The apparent viscosity of EPSs was correlated with the molecular characteristics.