Monoamine oxidase electrode in freshness testing of meat

Monoamine oxidase (monoamine: oxygen oxidoreductase, EC 1.4.3.4 from Aspergillus niger and beef plasma) was immobilized in a collagen membrane. An enzyme electrode consisting of a monoamine oxidase - collagen membrane (10 units) and an oxygen electrode was prepared for the determination of monoamines. Monoamines were oxidized to aldehydes by the immobilized enzyme and oxygen consumption was monitored amperometrically by the oxygen electrode. The response time of the electrode was 4 min. The optimum conditions for the enzyme electrode were pH 7.4 and 30°C. A linear relationship was observed between the amine (tyramine) concentration in the range 50–200 μm and the difference in current. No decrease in the output current was observed over an observation period of one week. The difference in current was reproducible with an average relative error of 8%. Monoamines in meat extracts were determined by the enzyme electrode.