DETERMINATION OF L-GLUTAMATE IN VARIOUS COMMERCIAL SOY-SAUCE PRODUCTSUSING FLOW-INJECTION ANALYSIS WITH A MODIFIED ELECTRODE

A now injection analysis (FIA) system with a modified electrode has be en developed and optimized for determination of L-glutamate using L-gl utamate oxidase (GLOD) (EC 1.4.3.11). GLOD was immobilized on controll ed-pore glass using glutaraldehyde. The optimal potential applied on t he working electrode was +700 mV against a platinum (Pt) reference ele ctrode. The optimal pH and flow rate of the carrier buffer were 7.4 an d 1.5 ml/min, respectively, A modified electrode was integrated into t he 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 obtaine d 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 electro active interference and was applicable to the determination of L-gluta mate in food samples. The modified FIA was faster and simpler than the more common methods of enzymatic and chromatographic analysis.