Poly(vinylferrocene)–poly(ethylene glycol) glutamate oxidase electrode for determination of L-glutamate in commercial soy sauces

An amperometric L-glutamate oxidase (GLOD) electrode based on a multilayer of polymer films was developed for the high selective determination of L-glutamate. The multilayer film consisted of three layers as the following configuration i.e., inner membrane of electropolymerized 1,3-diaminobenzene, middle layer of L-GLOD entrapped in photopolymerized poly(vinylferrocene)–poly(ethylene glycol) hydrogel polymer, and outer dialysis membrane. In this manner, the sensor could eliminate interferences and was able to work at a low potential poised at +0.085 V vs. Ag/AgCl. When used in a flow injection system, the sensor responded to L-glutamate in the range 0.5–8.0 mM, with a sensitivity of 9.48 nA mM^–1. The sensor was stable for 5 days of continuous uses (250 assays) and retained 60% activity after 16 days. When used to analyse the L-glutamate contents of a number of different off-the-shelf soy sauces, the sensor gave results in good agreement with the standard colorimetric method.     

Determination of l-glutamate in various commercial soy sauce products using flow injection analysis with a modified electrode

A flow injection analysis (FIA) system with a modified electrode has been developed and optimized for determination of l-glutamate using l-glutamate oxidase (GLOD) (EC 1.4.3.11). GLOD was immobilized on controlled-pore glass using glutaraldehyde. The optimal potential applied on the working electrode was +700mV against a platinum (Pt) reference electrode. The optimal pH and flow rate of the carrier buffer were 7.4 and 1.5ml/min, respectively. A modified electrode was integrated into the FIA system in order to eliminate electroactive interference and it was used to determine l-glutamate in 39 samples of Thai commercial soy sauce products. The results obtained were compared with those obtained from enzymatic assay using glutamate dehydrogenase and those from a chromatographic assay using an amino acid analyser. Good correlations were observed amongst these methods. The results indicated that use of an FIA system with a modified electrode was able to eliminate electroactive interference and was applicable to the determination of l-glutamate in food samples. The modified FIA was faster and simpler than the more common methods of enzymatic and chromatographic analysis.