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An amperometric biosensor has been developed for measurement of Umami, or the taste based on the amount of L-glutamate, in tomato foods. The biosensor is based on an enzyme-mediator system in which L-glutamate oxidase is used for biochemical oxidation of L-glutamate and a tetrafulvalene-tetracyanoquinodimethane (TTF-TCNQ) paste, prepared from the mixture of TTF-TCNQ salt, graphite powder, and silicone oil, serves as the mediator. The limit of detection, calculated by use of a four-parameter logistic model, was 0.05 mmol L(-1), and the limit of quantification was 0.15 mmol L(-1). The correlation coefficient (R2) was 0.990 and the relative standard deviation was no more than 1% (n=5). The response time (tau (95)) was 20-50 s, depending on concentration. The repeatability of the sensor was better than 5% (n=10). The sensor developed was stable for more than ten days.

Preparation and application of a conductive organic salt complex of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) for analytical bioelectrochemistry as a mediator is overviewed in this work. The third-generation biosensors based on this charge transfer salt are very promising for biosensors applied in vivo. Such mediated biosensors have been studied mainly for glucose determination, but at present other substrates are being applied in this system more and more often.

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