Biosynthesis And Recovery Of γ-Poly(Glutamic Acid)

As a kind of biological macromolecules,γ-Poly(glutamic acid) (γ-PGA) is water soluble , biodegradable , edible and non-toxic toward humans and the environment.Therefore,γ-PGA and its derivatives have been of interest in a broad range of industrial fields such as environment,medicine,food and cosmetics.The production ofγ-PGA has been recently focused on attentation.This thesis deals with the effects of agitation speeds onγ-PGA production by Bacillus subtilis NX-2 and batch fermentation kinetics of cell growth andγ-PGA synthesis.The recovery ofγ-PGA from highly viscous culture broth was also investigated.1.The results indicated that the agitation speeds had significant influences on the biosynthesis ofγ-PGA.The higher agitation speed would improve the transfer of oxygen and substrate,which increased the cell growth.However the speed over 600 r/min would damage extending of theγ-PGA chain and was unfavorable for the synthesis of large molecularγ-PGA.Under excessive agitation speed,fast cell growth led the glucose exhausting quickly.So the yield ofγ-PGA was not high.The highest yield ofγ-PGA obtained 21.78 g/L under 400 r/min.2.Based on experimental data of initial glucose concentration 40 g/L under 400 r/min,the kinetic equations of cell growth andγ-PGA production were established. Cell growth: = ddCt=[ 00.0.23824124033+CCexp(?0.138948C)?0.009842]Cγ-PGA production: rP = ddCtP= 3.993446 rX + 0.01397C X CG lm ? 0.013789CP With the initial glucose concentration from 30 to 60 g/L,the proposed kinetic equations provided an accurate approximation of theγ-PGA production by B. subtilis NX-2.3.An efficient strategy for the cellular separation and recovery ofγ-PGA from highly viscous broth were developed.By lowering the pH value of culture broth to 3,the viscosity of culture broth significantly decreased.After the acidification of culture broth,70.9 percent of cells were separated by nylon membrane of nominal pore...