A simultaneous assay method for L-glutamate and L-pyroglutamate contents in soy sauce using a 5-oxoprolinase (without ATP hydrolyzing activity).

L-Glutamine and L-glutamate, which are important flavor components in soy sauce, are converted to L-pyroglutamate during brewing. Therefore, it is necessary that the L-glutamate and L-pyroglutamate contents can be measured accurately. We developed a simultaneous assay method for L-glutamate and L-pyroglutamate by using 5-oxoprolinase (without ATP hydrolyzing activity) and glutamate oxidase. By this method, the L-pyroglutamate could be measured accurately in a range of 0.05 to 1.0 mM in the presence of 1.0 mM L-glutamate. This system is effective for process and quality controls.