Direct biosensor immunoassays for the detection of nonmilk proteins in milk powder

The low prices of some nonmilk proteins make them attractive as potential a dulterants in dairy products. An optical biosensor (BIACORE 3000) was used to develop a direct and combined biosensor immunoassay (BIA) for the simult aneous detection of soy, pea, and soluble wheat proteins in milk powders. A ffinity-purified polyclonal antibodies raised against the three protein sou rces were immobilized in different flow channels (Fcs) on the biosensor chi p (CM5). Dissolved milk powders were injected (20 muL injections at 20 muL min(-1)) through the serially connected Fcs, and the antibody-bound plant p roteins were detected directly. The total run time between samples, includi ng a regeneration step with 5 muL of 10 mM HCl, was 5 min. The limits of de tection in milk powder were below 0.1% of plant protein in the total milk p rotein content. The antibodies also recognized some proteins from other pla nt sources, which made this BIA even more suitable as a broad screening ass ay for nonmilk proteins.