Enzymatic determinations with rotating bioreactors: Determination of glutamate in food products Original Research Article

The benefits of using rotating bioreactors for on-line or in-line determination in food analyses are illustrated with the determination of l-glutamate. Two enzymatic approaches have been implemented and samples used to illustrate the approaches included: beef and chicken bouillon cubes, soy sauce, chicken broth, seasoning salt, fruit and vegetable juices, and skim milk. One of the methods uses glutamate dehydrogenase (EC 1.4.1.3) in the main enzymatic reaction and diaphorase (EC 1.8.1.4) in the indicator reaction, which involves NADH and hexacyanoferrate(III). The monitored species, amperometrically detected at a platinum-ring electrode, is the hexacyanoferrate(II) produced by the indicator reaction. The second method utilizes a single enzyme, glutamate oxidase (EC 1.4.3.11), and amperometric monitoring of a product of the enzymatic reaction, H2O2, also at a platinum-ring electrode. Interference by ascorbate present in some samples is eliminated by in-line use of a packed reactor containing ascorbate oxidase (EC 1.10.3.3). The relative merits of both systems when using continuous-flow/stopped-flow/continuous-flow processing are discussed.