The application of glutamic acid α-decarboxylase for the valorization of glutamic acid

Glutamic acid is an important constituent of waste streams from biofuels production. It is an interesting starting material for the synthesis of nitrogen containing bulk chemicals, thereby decreasing the dependency on fossil fuels. On the pathway from glutamic acid to a range of molecules, the decarboxylation of glutamic acid to γ-aminobutyric acid (GABA) is an important reaction. This reaction, catalyzed by the enzyme glutamic acid α-decarboxylase (GAD) was studied on a gram scale. In this study, GAD was immobilized on Eupergit and in calcium alginate and its operational stability was determined in a buffer free system, using various reactor configurations. Immobilization was shown to increase the GAD stability. The conditions for the highest GABA production per gram of enzyme were determined by extrapolation of enzyme stability data. At 30 °C in a fed batch process this results in an average volumetric productivity of 35 kg m⁻³ hr⁻¹. The cost of using GAD immobilized in calcium alginate was estimated as €5 per metric ton of product. Furthermore it was shown that the cofactor pyridoxal-5′-phosphate (PLP) could be regenerated by the addition of a small amount of α-ketoglutaric acid to the reactor. In conclusion the application of immobilized GAD in a fed batch reactor was shown to be a scalable process for the industrial production of GABA from glutamic acid.