Abstract:

In this study, the rheological properties of the neutral exopolysaccharide (EPS) produced by Streptococcus thermophilus ST1 isolated from spontaneously fermented products were studied. The results showed that the aqueous EPS solution was a typical non-Newtonian pseudoplastic fluid, and its flow behavior was affected by concentration, temperature, shearing time and pH. The viscosity of EPS solutions increased when the concentration was increased. The higher the concentration was, the more serious the phenomenon of shear thinning was. The viscosity of EPS solutions had little change with good temperature resistance at 10 － 80 ℃. With increasing shearing time from 0 to 900 s, the solution viscosity always showed a downward trend. The viscosity of the EPS solution at pH 4 was relatively stable, while the viscosity at pH 7 and pH 10 greatly decreased with increasing shear rate. The viscosity of skim milk was significantly increased by adding 1 g/100 mL EPS. However, as the shear rate was increased, the viscosity-enhancing effect became smaller.

Key words: exopolysaccharide, Streptococcus thermophilus ST1, rheological properties