Structural characterization of exopolysaccharide produced by Streptococcus thermophilus and rheology of mixed protein-polysaccharide systems

This study determined the constituents and structural properties of extracellular polysaccharides of Streptococcus thermophilus (STEP) and investigated the rheological properties of the blended system of STEP and whey protein (STEP/WP). Two STEP, neutral polysaccharides (STEP-1) and acidic polysaccharides (STEP-2), were isolated and purified from S. thermophilus. Their molecular weights were 2197.74 and 141.99 kDa, respectively. STEP-1 were mainly composed of galactose, glucose, and rhamnose, whereas STEP-2 were mainly composed of galactose, mannose, and glucose. Methylation and NMR analyses confirmed that the STEP structural backbone included α- and β-type pyranose residues and many branching structures. The rheological results revealed that the apparent viscosity of STEP/WP was higher than that of STEP, while STEP/WP mainly acted as a viscous liquid under the influence of dairy processing parameters. These findings may be useful for STEP/WP application in the production of dairy products such as fermented milk and cheese. [Display omitted]