Simultaneous biosensing of inosine monophosphate and glutamate by use of immobilized enzyme reactors

The simultaneous determination of inosine monophosphate (IMP) and l-glutamate (GL), by enzyme-supported flow injection analysis (FIA), was performed using two enzyme reactors in parallel. Inosine monophosphate dehydrogenase (IMPDH) was extracted and partially purified from Bacillus cereus (JCM 2152). The reaction of IMP with NAD+ was catalyzed by IMPDH and the NADH produced was further converted to NAD+ and hydrogen peroxide by NADH oxidase. GL was determined by using the enzyme glutamate oxidase. Thus, IMP and GL were indirectly measured by monitoring hydrogen peroxide electrochemically. The ghost response caused by the presence of interferences in real sample were reduced by covering the platinum electrode surface with a diaminobenzene polymer membrane which was generated by elctropolymerization. Linear relations between sensor response and each species were observed in the ranges of 0.1–1.0 mM (IMP) and 0.05–1.0 mM (GL) with correlation coefficients >0.997 for each species. The proposed method was used for seasoning analyses and the results showed good agreement with those obtained using a liquid chromatographic method (for IMP) or a conventional method (for GL with a kit), suggesting that this system may be applicable to the quality evaluation of food seasoning.