Determination of aspartame in dietary food products by a FIA biosensor

A flow injection analysis (FIA) biosensor system was developed for the determination of the artificial sweetener aspartame (N-l-α-aspartyl-l-phenylalanine methyl ester). The system consisted of two enzyme columns, containing purified peptidase and aspartate aminotransferase respectively, immobilized on activated aminopropyl glass beads and an enzyme electrode connected in series. The dipeptide bond of aspartame was cleaved by immobilized peptidase to release aspartic acid which was in turn transaminated by aspartate aminotransferase. The glutamate produced by transamination was monitored by the enzyme electrode which used l-glutamate oxidase immobilized on a nylon membrane in combination with a hydrogen peroxide electrode. The response of the FIA biosensor was linear up to 1 mm aspartame with a lower detection limit of 20 μm and had good reproducibility (r.s.d.2·2%). The FIA biosensor was stable for at least 30 h of continuous use at room temperature and the immobilized enzymes were stable for at least 1 month when stored in buffer at 4°C. Each assay takes ca. 7-8 min giving a sample throughput of 8 h^-1. When applied to aspartame measurements in dietary food products, the results obtained agreed well with those reported by the product manufacturer.