| γ-Aminobutyric acid (GABA) is the most important inhibitory transmitter in the central nervous system (CNS). It has many kinds of physiological functions, such as calming, promoting sleep, enhancing memory, curing epilepsy and hypertension, controlling asthma, regulating hormone secretion, promoting procreation, activating liver and kidney function.This paper studied the separation process of GABA from broth fermented by a Lactobacillus brevis strain systematically. A simple and effective procedure, comprising flocculation, decolorization, ion exchange and crystallization, was brought forward. The operating conditions of each step were discussed in detail. The recovery of GABA in the whole process was about 50%, and the purity of the ultimate product could reach 98%.Single-factor experiments using chitosan as the flocculant showed that pH and flocculant dosage could influence flocculation strongly, while the effect of temperature on flocculation was not so obvious. When pH was about 4-5, flocculant concentration about 100-200ppm, and temperature about 30℃, the flocculation was effective. Then an orthogonal experiment was carried out., the result of which showed that the order of importance was pH, flocculant dosage, and temperature. The optimum pH was pH 5.0, flocculant concentration 100ppm, and temperature 20℃. Under such conditions, flocculation ratio could reach 97.3%, while the loss of GABA was only about 1.2%. Comparison between flocculated and not-flocculated broth showed flocculation also could improve filtration effectively.After screening from three types of macroreticular resins, we found SD300 exhibit high decoloring ratio and high GABA yield. The decoloring ratio of SD300 increased as pH fell down. However, when pH was below 5, there might be a lot of loss of GABA. Comprehensively considering decoloring ratio, GABA yield and convenience of operation, keeping pH 5.0 was a good idea. Raising temperature could improve decoloring ratio to some extent, but it would also result in decrease of GABA yield, so during the decoloring process we'd better just keep fermented broth at room temperature. Dynamic absorption experiments showed that the optimum flow velocity and loading volume was 2BV(Bed Volume)/h and 6BV, respectively. Under theseoptimum conditions, decoloring ratio could reach 93.2%, and GABA yield reached 86%.After screening from nine types of ion-exchange resins, we found DOOl was an ideal ion-exchange medium, which had both a high exchange capacity and a high exchange velocity. Static experiments using DOOl (H+ type) as the ion-exchange material showed that DOOl had a high and almost unvaried exchange capacity in the pH range of 3 to 6.2. Out of this range, the capacity decreased obviously. Adsorption isotherm under the room temperature was plotted, which showed that even if GABA concentration was very low DOOl still possessed a high exchange capacity. Dynamic loading experiments showed that the optimum flow velocity was lOBV/h, and there was no need to dilute loading solution. Further study on dynamic elution revealed that loading quantity was an important factor which affected separation greatly, so it's necessary to optimize the loading quantity before elution. In our experiment (GABA concentration was 0.42mol/L and flow velocity lOBV/h), the optimum loading quantity was about 3BV. The concentration of the eluant, ammonia water, shouldn't be too high or too low, 2mol/L was a recommended value. During this whole step, the recovery of GABA was 92%.The preliminary study on the crystallization of GABA was also carried out. The results showed that even when the temperature was about 0°C, the saturated concentration of GABA was still great, so we'd better not just use simple cooling method to crystallize GABA. By integrating alcohol-adding with cooling, we got colorless columnar crystals of GABA, which belonged to triclinic system. The purity of these crystals could reach above 98%. During this step, the recovery of GABA was 64%.
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