Chromatography Separation Of Gamma-Aminobutyric Acid And Monosodium Glutamate

Gamma-aminobutyric acid, a major inhibitory neurotransmitter in the mammalian central nervous system, has been widely applied in many foods and pharmaceuticals. The food-grade gamma-aminobutyric acid is mainly produced by microbial fermentation. However, due to the complexity of the fermentation broth which contains monosodium glutamate, pigment, salt and other impurities,it is quite difficult to separate gamma-aminobutyric acid from the broth. This paper aims to establish a green and highly efficient chromatographic method to separate gamma-aminobutyric acid from fermentation broth, and to study the mass transfer mechanism of gamma-aminobutyric acid and monosodium glutamate, which can lay a foundation for further study on separation of gamma-aminobutyric acid from fermentation broth in industrial scale.Firsr of all, the optimal resin that can separate gamma-aminobutyric acid and monosodium glutamate was systematically selected from 8 kinds of resins, and the influences of ratio of length to diameter of column, flow rate of mobile phase and column temperature on the separation efficiency of gamma-aminobutyric acid and monosodium glutamate were investigated according to resolution and recovery. The results showed that the resin QY-HG01 separated gamma-aminobutyric acid and monosodium glutamate well. The best separation efficiency was achieved under the operating conditions of ratio of length to diameter 25, flow rate of mobile phase 2.5 mL/min and column temperature 50℃ through the single factor experiments. The separation mechanism of gamma-aminobutyric acid and monosodium glutamate was also investigated, and it was found that the separation of gamma-aminobutyric acid and monosodium glutamate is mainly caused by the Donnan exclusion. Injected with the pretreated fermentation broth, it was found that gamma-aminobutyric acid and monosodium glutamate separated well, and the decolorization rate of the fermentation broth was 84.9%, the desalinization rate was 99.2%, the purity of gamma-aminobutyric acid increased from 24.9% in broth to 80.4% in eluent with 89.3% recovery yield by one-step treatment.Secondly, the equilibrium isotherms of gamma-aminobutyric acid and monosodium glutamate were measured by frontal analysis while the overall mass transfer coefficients, axial dispersion coefficients and bed voidages of the column were determined by moment analysis. The results showed that the gamma-aminobutyric acid and monosodium glutamate equilibrium isotherms were both of linear type and the selectivities of gamma-aminobutyric acid against monosodium glutamate were 7.33,7.34,7.04 at temperatures of 40℃,50℃, and 60℃. For the homogeneous column QY-HG01, the values of external porosity ε, total porosity εT, and internal porosity εP were 0.45,0.86,0.75 respectively. The overall mass transfer coefficients of gamma-aminobutyric acid were 0.53 min-1、0.58 min-1、0.71 min-1 and MSG’s overall mass transfer coefficients were 0.18 min-1、0.25 min-1、0.28 min-1 at temperatures of 40℃,50℃, and 60℃. The values of the mass transfer coefficient of gamma-aminobutyric acid and monosodium glutamate were both small according to their magnitudes, which indicated that the mass transfer rates on this column were slow and the band broadening that km caused could not be ignored. So the lumped kinetic model was used to simulate the separation process of the gamma-aminobutyric acid and monosodium glutamate.At last, the lumped dynamic model was solved by MATLAB software, and the simulated breakthrough and elution profiles were obtained, which were going to be compared with the experimental values. The results showed that the simulated breakthrough and elution profiles matched the experimental data well, which verified that the selected model and the measured parameters can successfully predict the separation process of gamma-aminobutyric acid and monosodium glutamate. This also proved that the assumptions of (ⅰ) a non-competitive adsorption between gamma-aminobutyric acid and monosodium glutamate and (ⅱ) the presence of the other impurities in the fermentation broth will not affect the peak time of gamma-aminobutyric acid and monosodium glutamate did not significantly influence the precision of the model predictions. These results provided good theoretical guidances and technical support for the design of simulated moving bed and the industrial scale-up of the chromatography column in the future.