Influences of pH and electrolyte on the rheological properties of aqueous solution of exopolysaccharide secreted by a deep-sea mesophilic bacterium

The effects of pH and electrolytes (NaCl and CaCl2) on the viscosity, dynamic modulus (storage modulus G′ and loss modulus G″) and thixotropy of aqueous solution of new exopolysaccharide (SM-A87 EPS) secreted by a deep-sea mesophilic bacterium Wangia profunda SM-A87 were investigated. It was found that at pH 3–12 and the electrolyte concentration of 0.1–80 g/L, the SM-A87 EPS solution showed very weakly pH-dependent and salt-dependent rheological properties and dominant elastic behavior. These properties were considered to arise from the hyper-branched structure of the SM-A87 EPS molecules through the comparison of rheological properties of SM-A87 EPS solutions with those of partially hydrolyzed polyacrylamide ones at different electrolyte concentrations. Such good pH stability and salt resistance of the SM-A87 EPS solution indicate that SM-A87 EPS has great potential for application as food additive, thickener, stabilizer and enhanced oil recovery system. In the studied conditions, 2 g/L SM-A87 EPS solution showed positive thixotropy. The relative thixotropic recovery decreased with pH increasing and the electrolyte concentration decreasing.