Abstract
A selective and sensitive on-line monitoring system for diacetyl, based on a biosensor, was developed forapplication in the brewing industry. The biosensor consists of an enzyme reactor coupled with either amperometric orphotometric detection in a flow injection analysis (FIA) design. The reactor was packed with the enzyme diacetyl reductase(EC 1.1.1.5) immobilized onto aminopropyl controlled-pore glass (CPG) beads. An amperometric glassy carbon electrode,chemically modified using the organic dye toluidine blue (TB), was able to monitor the amount of coenzyme NADPH oxidizedin the reactor. The detection limit of the biosensor was 5.8 10-6 M of diacetyl with an error of 14%. An alternative opticaldetection scheme, based on absorbance at 340 nm, was also evaluated. This resulted in lowering the biosensors detectionlimit of diacetyl to 2.3 10-7 M with a 4% error at 5.8 10-6 M. The immobilized enzyme reactor columns were stable for45 days and gave consistent data for at least 30 diacetyl measurements on laboratory beer before there occurred a significantdecrease in enzyme activity.
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