COMPARISON OF 2 ENZYME SEQUENCES FOR A NOVEL L-MALATE BIOSENSOR

Two novel amperometric biosensors for the determination of L-malic aci d in food samples have been compared. Both sensors make use of a Clark -type O-2-electrode but differ in the enzymes used. The first sensor i s composed of malate dehydrogenase (decarboxylating), also known as 'm alic enzyme' (MDH(dec.), EC 1.1.1.40) and pyruvate oxidase (POP, EC 1. 2.3.3). It covers a linear detection range from 1 mu mol dm(-3) to 0.9 mmol dm(-3) L-malate, with a response time of 1.5 min (t(90)) and a r elative standard deviation of 3.5%. Measurements with real samples off ered a good correlation with the standard enzymatic assay (difference +/-7%) Stored at room temperature, the response of the sensor is const ant for 8 days. The second biosensor is based on the three enzyme sequ ence malate dehydrogenase (MDH, EC 1.1.1.37), oxaloacetate decarboxyla se (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3). It has a non-linear calibration curve. Concentrations from 5 mu mol dm(-3) to 1 mmol dm(-3) L-malate can be detected, within a response time of 1.5 m in and with a relative standard deviation of 20%. The lower detection limit for L-malate is 2 mu mol dm(-3). The response is constant for 10 days when the sensor is stored at room temperature.