Study On Preparation,Structure And Rheological Properties Of Exopolysaccharides From A Streptococcus Thermophilus AR333

Streptococcus thermophiles has been recognized as second most used bacterium in dairy industry.The EPS from Streptococcus thermophiles always was used as natural stabilizer.Compared with chemical additives and plant additives,it was secreted into products directly and reducing the costs considerably.This paper screened out a Streptococcus thermophiles strain AR333 from naturally fermented dairy products.The EPS from AR333 were prepared and purified.The purified EPS was further studied by the physicochemical properties,composition,structural characteristics and rheological properties analysis.AR333 was identified as Streptococcus thermophiles.Its production of EPS has reached 257 mg/L after optimization.The EPS from AR333 were purified through DEAE-Sepharose Fast Flow,resulting a neutral fraction which was designated as EPS333.The homogeneity of EPS333 was checked by Sepharose CL-6B.In vitro test showed that EPS333 could stimulate macrophage RAW 264.7 to release NO significantly?P<0.05?.The M_w?314 kDa?,M_n?176 kDa?,polydispersity index?PDI,1.78?and R_g?33.96nm?of EPS333 was determined by HPSEC.The M-H coefficient??1.04?showed that EPS333 was in extension and rigid rod conformation in aqueous solution.Intrisic viscosity[?]in solution of 0.1 mol/L NaNO₃ was determined to be 1.81 d L/g by Ubbelohde viscometer.The monosaccharide composition of EPS333 was determined to be galactose and glucose in a molar ratio of 2:1 by HPAEC.Methylation and GC-MS analysis revealed that EPS333 was consisted of T-Galp,1,3-Galp,1,4-Glcp and 1,3,6-Glcp in a molar ratio of 2:4:1:2.N-acetyl groups and the backbone of EPS333 were proposed according to the methylation and NMR results as well as previous reports.The rheological behaviors of EPS333 solutions were studied using steady-shear and dynamic oscillatory measurements.The various concentrations of EPS333exhibited as shear thinning non-Newtonian behavior and showed no thixotropic phenomenon.Its stability against time,salts,temperature and wide range of pH made it a good thickener and stabilizer in food formulation.By compared with other starter,yogurt fermented by AR333 showed higher viscosity and water holding capacity.