Fermentation Production Process Of Novel Microbial Polysaccharide-Welan Gum

Welan gum is a kind of soluble extracellular polysaccharide produced by Alcaligenes sp. ZW-3 (previously named S-130) in an aerobic submerged fermentation. It is one of the most market prospective microbial polysaccharides developed by Kelco, a company of American. As reported that welan gum in aqueous media has excellent rheological properties, and its special molecular structure has attracted the extensive attention of oil well drilling fluids, building industry and food industry.In this thesis, the nutritional and environmental requirements for optimal polysaccharide production were carried out. The rheological property of welan gum solution was studied. The progresses of isolation and separation of welan gum from fermentation broth were investigated, and the structure of the purified welan gum was analyzed. The main works and results are as follows:The effects of different carbon sources and nitrogen sources and the optimum concentration of other medium components on the fermentation of welan gum were investigated. Plackett-Burman design was undertaken to evaluate the effects of eight factors. With statistic regression analysis, the significant factors affecting polysaccharides production were determined as follows: sucrose, NaNO3 and CaCO3. Central composite design was used to optimize the three critical internal factors mentioned above, and the optimum concentration of the variables was determined as follows: sucrose 102.0 g/L, NaNO3 4.0 g/L, CaCO3 5.9 g/L. Under such conditions, the yield increased to 28.25 g/L and the viscosity was up to 22 Pa s, which was 111.77% and 89.66% higher than the maximum value in the single factor tests. The optimized environmental condition as follows: inoculation amount is 6%, medium volume is 100 mL/500 mL, initial pH is 6.5 ~ 7.0, the welan gum synthesis temperature is 30℃. The primary study of fermentation performance was carried out on 5 L and 30 L bioreactor. Since the mass transfer and mixing efficiency can not meet the needs of high-viscosity fermentation, the yield of welan gum was 16 g/L and the viscosity was 32 Pa s.A novel method for determining rheological behaviors indexes of non-newtonian fluid was developed by using rotational viscometer, and the rheological property of welan gum solution was studied. The relantion between viscosity and shear rate, pH and temperature was investigated. The results showed that the solution of welan gum is a typical pseudoplastic fluid. It has the outstanding high temperature resistant property and has the excellent stability towards pH 2 ~ 13, which showed widely applications future compared with xanthan gum.The effects of temperature, pH and salts on the separation of welan gum from fermentation broth were studied. The results showed that the optimum extraction parameters were determined: the concentration of NaCl is 1.6%, pH is 4 ~ 5, the heat treatment is 40℃. The components of analytic sample were identified by Ion chromatography and IR, results showed that it contains rhamnose, glucose, mannose, galactose and glucuronic acid. The respective percentages are 36.06%,32.58%,8.98%,5.28%,14.33%. The content of acetyl is 5.8375%. The polysaccharide was mainly consisting ofβglucosidic linkages.