| Streptococcus salivarius subsp. thermophilus LCX200I was selected as the strain for the production of exopolysaccharides. This study aimed at finding an operative way leading to high yield of exopolysaceharides and studying physiological functions of exopolysaccharides produced by Streptococcus salivarius subsp. thermophilus LCX200I. The main research results were as follows:The Phenol-sulphuric method used as EPS concentration assay was studied, and this method had an average relative error of 0.2%.Numerous lactic acid bacteria had been examined for their exopolysaccharides production capacities. The results clearly shown that the highest yield of EPS produced by lactic acid bacteria in 34 strains was Streptococcus salii~ariz.c subsp. thermophilus LCX200 1.The effect of carbon source, nitrogen source , salt and the optimum initial ~ I-I value of medium on EPS produced by S salivarius subsp. thermophillus were studied. From MRS, Ml 7, ATh, SL, Elliker and 5DM which were used as lactic acid bacterium basic culture media, a new culture medium (named as LCX) for the synthesis of exopolysaccharides by Streptococcus salivarius subsp. thermophilus LCX200 I was formulated. The suitability of the semi-defined culture medium was obtained, the medium had following compositions:feptone, 1.5%; tryptone, 1.0%; glucose, 1.0%; lactose,l .0%; K2HPO4, 0.2%; MgSO4.7H20, 0.02%; MnSO4.4H20, SOmg/L; Tween 80, lmL/L; Sodium acetate, 0.5%; Sodium glycerophosphas, 1.9%.Exopolysaccharides production was studied by growing Streptococcus salivarius subsp. thermophilus LCX200I in LCX. The best culture conditions for Streptococcus salivarius subsp. thermophilus to synthesis EPS were that inoculation amount is 2% of cultures with fermentation at 350C for 20h.Constant pH method and fed-batch method for exopolysaccharides produced by Streptococcus salivarius subsp. thermophilus LCX200 1 was compared. It was found that these two methods both could increase EPS produced by Streptococcus salivarius subsp. thermophilus LCX200I. The constant pH was 5.5, the growth of cells show moderately, but EPS production with the constant pH method \~as higher than with the batch method. The yield of EPS under constant pH was 347mg/L, and with th~ fed-batch method wasæ‹i38mg/L.Batch fermentation process and the kinetics of the exopolysaccharides produced by Streptococcus salivarius subsp. therm ophilu.s LCX200 I were studied. The mathematical kinetics models describing the course of EPS fermentation were obtained, which reflected the relationship among growth of cell, lactic acid production, EPS synthesis and the consumption amount of substrate. The relative deviations between the experimental data and calculated results were no more than 10%.The quadratic rotary combination design was used for studying the EPS produced by Streptococcus sa!ivarius subsp. thermophilus LCX200 I in tofu whey. The mathematics models of the study were established and the optimal conditions were obtained as followed:pH was 6.3, culture temperature was 360C, peptone was 2.0%.The exopolysaccharides produced by Streptococcus salivariu.s subsp. thermophilus LCX200 I from fermented broth were extracted under the following conditions: the fermented broth was stirred at 500 rpm and, concentrated to 1/5 of initial volume and, was adjusted topH 6.5, exopolysaccharides were precipitated with ethanol at concentration of 70% (v/v) at 25C for 3h, or at 4Cfor 12h and, was centrifuged at l0000g for 20 mm.The exopolysaccharides were purified on a chromatography column of sepharose CL-6B, volume of sample was lOmL, concentration of sample was 4Omg/mL, eluted wit!~ water at a flow rate of 45mLIh. Molecular weights of EPSI and EPS2 were 1.2/ 106 and 3.8/ 10~ Dalton respectively. The monosaccharides compositions of EPS I were glucose and galactose in the molar ratio of 1:4 by hydrolyzing EPS 1 with sulphuric acid and then analyses with HPLC. The data of JR revealed that EPS 1 was constituted chiefly with 13-glycosidic bonds.Rheological and sensoty propert...
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