Screening Of Microbial Strain With Xanthan Gum And Optimizing Of Fermentation Conditions

In this thesis, the fermentation of xanthan gum is investigated. In this thesis we studied on how to improve the fermentation of xanthan levels. At first, Select breeding of Xanthomonas campestris strain A-1 Xanthan. The yield of xanthan from original strain wss only 15.46g/L. The xanthan fermentation yield can reach 18.75g/L by UV mutation and stability experiment. Then, used the strains which from UV mutagenesis for nitrosoguanidine mutagenesis and genetic stability experiment. The xanthan fermentation yield can reach 21.63 g/L. The yield of xanthan gum has significantly increased, called the breeding Xanthomonas campestris strain A-2.Based on getting high-yield strains successfully, studied the effect of fermentation medium on xanthan fermentation yield. We taked corn starch as a carbon source by single factor experiment, the additive amount was 4.5%. Taked Soybean meal as a nitrogen source, the additive amount was 0.5%. After that, made an response surface experiment of fermentation medium. Find the effect of fermentation medium composition on the response of surface experiment. Screening of corn starch and soybean meal as two significant factors, determining the concentration of corn and soybean meal from the steepest ascent and central composite experiment. The xanthan fermentation yield can reach 27.32 g/L when added 5.78% corn starch and 0.52% soybean meal.Fermentation conditions also have a high impact for the strain growth and production of xanthan gum. By measuring the OD600 of the thallus obtained, the optimum conditions for cell culture is pH value 6.8, temperature 26℃, stirring speed 180r/min, inoculation of 6%, the growth period of 20h, the inoculation time is at 18h . From Single-factor experiment and orthogonal experiment that can get the optimal fermentation conditions for producing xanthan gum is: pH7.0, growth temperature 28℃, rotational speed 220 r/min, inoculations 6%. The yield of strain was come up to 29.5g/L.At last, the paper make a study on the post-processing of Xanthan gum fermentation liquor. On the one hand, the fermentation broth diluted 1-fold and filtered through diatomaceous earth. The diatomite addition level was 10g/L, xanthan gum yield was 93%. On the other hand, the xanthan gum yield can reach 98% through zymolysis. The Alcalase addition level was 100U/g, hydrolysis temperature was 35℃. Then analysis the pretreated fermentation liquid by alcohol, using 95% ethanol as solvent alcohol analysis, alcohol consumption was 1 times untreated fermentation broth, the alcohol analys was pH 5.5. Obtained by the determination of physical and chemical indicators, the 1% xanthan gum solution viscosity was 1516cp, shear performance was 7.15, the water content was 9.2%, ash 7.6g/100g. Xanthan gum can dissolve in water, the Xanthan gum will form gels when add Locust Bean Gum.