Effects Of Different Impellers And Surfactants On Xanthan And Poly-γ-Glutamic Acid Fermentation

The biosynthesis of product such as xanthan gum and poly y-glutamic acid (y-PGA) is a high-viscosity fermentation system, oxygen transfer velocity and mixing efficiency of high-viscosity fermentation system is limited, and much more power consumption during the fermentation is needed, so, it is the most important factors which limited the industrial development of these products.In this paper, the effects of different surfactants and impeller combination on the fermentation of xanthan gum andγ-PGA were investigated.The optimization of xanthan gum production of Xanthomonas campestris had carried out in flaskes. The optimal fermentation medium was (g/L):sucrose 40, soybean flour 4, cirtic acid 2, MgSO4·7H2O 1, K2HPO4 1, CaCO3 2.The optimal cultivation conditions:temperature 30℃, inoculum age 16 h, inoculum size 10%, initial pH 7.0.Using the optimal fermentation parameteres, the xanthan gum yield reached 27.55 g/L, the broth viscosity reached 5833 mPa·s, increased by 43.71% and 63.53% respectively, as compared with that of the initial conditions.the conversion rate of carbon source reached 68.88%.The effects of adding different surfactants on xanthan fermentation were studied, such as Triton X-100, sodium dodecyl sulfate (SDS), dimethyl sulfoxide (DMSO), oleic acid and Tween 20.Results showed they were conducive to improve the broth viscosity by adding an appropriate dosage of surfactants on a certain time (24 h-48 h) in broth. When cultivated for 36 h, by addition of 0.1% Triton X-100, the high broth viscosity were obtained(8163 mPa·s) increased by 36.51% as compared with that of the control, but the yield of xanthan gum did not change significantly.The effects of different combination of impeller and pH regulation on xanthan fermentation were investigated in 3 L bioreactor. Six upflow bladed disc turbine +Semi-tubular disc turbine (PDTD (U)+HY) was the optimized combination, using the optimal impeller combination, the broth viscosity had increased significantly compared with that of the control (Six straight blade disk turbine+Six straight blade disk turbine, DT+DT), but the yield of xanthan gum has not increased significantly. The Six straight blade disk turbine combination(DT+DT) and the optimal impeller combination(PDTD(U)+HY) was used for the study of control pH7.0 during xanthan fermentation, the broth viscosity was increased by 56.67% and 125.00% compared with that of the control(DT+DT, pH nature),but the yield of xanthan gum only increased slightly. The effect of different surfactants on y-PGA production from B. licheniformis WX-02 was investigated. Among six surfactants, anionic surfactant SDS played an important role in enhancing y-PGA production, the optimum addition time and addition dosage were 12 h and 0.05%(V/V).Under the optimal addition condition, the y-PGA yield reached 20.95 g/L, increased by 1.06 times as compared with that of the control (without SDS).Although cell growth was significantly inhibited at the protophase(12 h-16 h) of adding SDS,the whole fermentation period was not extended. SDS addition benefited the capsule removal of B. licheniformis WX-02 during fermentation, which may be one of the reasons for the enhancement of y-PGA production by adding SDS.When treating seed with sodium dodecyl benzene sulfonate (SDBS), B. licheniformis WX-02 can be induced to product a high-level of y-PGA (26.78 g/L), and the high sodium glutamate apparent conversion rate (66.95%) was obtained, increased by 86.62% as compared with that of the control. The y-PGA productivity per unit of biomass (YP/X) reached 3.31 g/g, increased by 51.83% as compared with that of the control. The increased YP/X showed the enhancement of y-PGA biosynthesis may be a response when B. licheniformis WX-02 was subjected to SDBS stress, suggesting the y-PGA might contribute to protect B. licheniformis WX-02 from the surfactant stress.The different impeller combination(PDTD(U)+HY, PDTD(D)+6BM and PDTD(U)+6BM) can enhance the y-PGA fermentation, and the optimal combination was PDTD(U)+6BM, under the optimal combination conditions, the broth viscosity and the yield of y-PGA increased by 40.90% and 11.50% compared with that of the control(DT+DT).