l-Glutamate determination in food samples by flow-injection analysis Original Research Article

This work refers to the exploitation of green pepper (Capsicum annuum) as an enzymatic source of l-glutamate decarboxylase for the development of enzymatic reactors for automatic continuous flow systems. The purified enzymatic extract was immobilised in glass beads, incorporated into an assembly with potentiometric detection and applied to the determination of l-glutamate in food formulas of commercial soups. The enzymatic reactor with 8 cm length and 4 mm thickness was filled with 400 mg of beads containing the immobilised enzyme with a specific activity of 4.12 U mg−1 of protein and a useful life time of 78 days or 638 determinations. Optimisation of the flow system by response surface methodology allowed its application to the determination of l-glutamate in the range 2.5–75 mmol l−1 for 200 μl samples with a sampling rate of 60 samples per hour. The results obtained with the proposed methodology were compared with those obtained by spectrophotometric determination, showing relative deviations lower than 5%.