Bienzymatic amperometric sensor for protein assay in milk

A new bienzymatic amperometric sensor is proposed for the assay of the protein content of milk. The sensor is based on two enzymes: carboxypeptidase A and L-amino acid oxidase. The response characteristics obtained for this sensor (detection limit of 1.5 micromol/L, linear concentration range between 1.8 and 2.8 micromol/L), as well as high selectivity over possible interferences from milk, made it applicable as a detector in flow injection analysis (FIA). The response characteristics obtained in the non-equilibrium conditions (FIA system) are: detection limit of 1.5 micromol/L and linear concentration range between 2 and 3.5 micromol/L. Without FIA, the average recovery of proteins from milk and milk products is 99.06 +/- 0.07% and, by utilization of FIA, it increased to 99.73 +/- 0.03. The sensor proved a good reliability for the assay of proteins in milk and milk products.