title: Monitoring of alpha-ketoglutarate in a fermentation process using expanded bed enzyme reactors.
abstract: A bienzyme flow injection system is presented for the monitoring of alpha-ketoglutarate produced in a fermentation process, using glutamate dehydrogenase (GDH) and glutamate oxidase (GlOx) immobilised in two serially connected expanded bed reactors. The use of expanded bed resulted in unhindered passage of the bacterial cells through the columns, and thereby the need of a separate filtering step (e.g. microdialysis) was avoided. In the first reactor, alpha-ketoglutarate was converted to L-glutamate by GDH in the presence of ammonia and NADH. In the following reactor, L-glutamate was converted by GlOx to alpha-ketoglutarate, ammonia and hydrogen peroxide, which was detected in an electrochemical flow-through cell at +650 mV vs. Pt/(0.1 M KCl). The detection limit of alpha-ketoglutarate in the coupled packed bed reactors was 1 microM (defined as 3 S/N), the linear range 0-100 microM, and the sensitivity 0.80 nA/microM (R(2) 0.99). In the coupled expanded bed reactors, the detection limit of alpha-ketoglutarate was 7 microM (defined as 3 S/N), the linear range and the sensitivity being 0-500 microM and 0.11 nA/microM (R(2) 1.00), respectively. The response time (defined as the time between peak rise and return to baseline) was 5 min for coupled packed beds (injection of supernatant), and 12 min for coupled expanded beds (injection of sample containing cellular and particulate matter). Several other parameters, such as reactor stability, flow rate dependency, bed expansion, glutamate interference, etc. were investigated and characterised. When analysing real samples from a fermentation broth, the same results were obtained independent of the nature of the reactor system (packed or expanded bed). The hereby described system can easily be automatised and controlled from a personal computer.
authors.affiliation: Department of Biotechnology, Center for Chemistry and Chemical Engineering, Lund University, P.O. Box 124, S-221 00 Lund, Sweden.
authors.forename: A
authors.initials: A
authors.lastname: Collins
authors.forename: M P
authors.initials: MP
authors.lastname: Nandakumar
authors.forename: E
authors.initials: E
authors.lastname: Csöregi
authors.forename: B
authors.initials: B
authors.lastname: Mattiasson
mesh_terms: D000594:Amino Acid Oxidoreductases; D019149:Bioreactors; D015374:Biosensing Techniques / Q000295:instrumentation*; D004800:Enzymes, Immobilized; D005285:Fermentation; D017022:Flow Injection Analysis; D005969:Glutamate Dehydrogenase; D007656:Ketoglutaric Acids / Q000032:analysis* / Q000378:metabolism
chemical_list: D004800:Enzymes, Immobilized; D007656:Ketoglutaric Acids; D000594:Amino Acid Oxidoreductases; D005969:Glutamate Dehydrogenase; C020651:D-glutamate oxidase