Fluorometric biosensing of the total amino acid content and the glutamate content of green tea infusions using an automated multi-channel flow system

An automated multi-channel continuous-flow analyzing system was constructed for the rapid measurement of both the total amino acid content and the L-glutamate content of green tea infusions. L-Glutamate in samples was oxidized and deaminated enzymatically in a channel with a mini-reactor that was packed with L-glutamate oxidase immobilized on glass beads, and the evolved ammonium ions were measured by a fluorogenic reaction with o-phthalaldehyde and beta-mercaptoethanol. The total amino acid content was measured in a channel with another mini-reactor which was filled with immobilized L-amino acid oxidase. The fluorometric method is not subject to interference by reducing substances such as tea catechins and ascorbate, and the analytes in tea infusions were measured without pretreatment of samples. The use of this system for evaluation of tea quality was investigated.