In the biofermentation 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 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 GABA were successfully avoided, and GABA crystals with cuboid shape and good dispersion were prepared.

中文翻译：

---

了解上游杂质对γ-氨基丁酸的上油和结晶的影响

在γ-氨基丁酸（GABA）的生物发酵合成过程中，发酵液中会产生多种杂质，这些杂质可能会引起油污现象，进而影响后续分离过程中的工艺稳定性和晶体质量。在这项工作中，在不同浓度的杂质存在下，构建了水-乙醇混合物中GABA的相图。在相图中已证明，杂质含量的增加可加宽注油区域。此外，上油会严重抑制晶体生长并导致产品结块。在这项研究中，通过控制低杂质浓度下的结晶，成功避免了GABA的上油和结块，