Understanding the effects of upstream impurities on the oiling-out and crystallization of γ-aminobutyric acid

In the bio-fermentation synthesis process of γ-aminobutyric acid (GABA), a variety of impurities can be generated in the fermentation liquor, which could induce the oiling-out phenomenon and then affect the process robustness and crystal qualities during the subsequent separation procedure. In this work, the phase diagrams of the GABA in the water-ethanol mixtures were constructed in the presence of different concentrations of impurities. It was demonstrated that an increase in the impurity contents could broaden the oiling-out zone in the phase diagram. In addition, oiling-out can seriously inhibit the crystal growth and result in agglomeration of the product. In this study, by controlling the crystallization at a low concentration of impurities, oiling-out and agglomeration of the GABA were successfully avoided, and GABA crystals with cuboid shape and good dispersion were prepared.