A comparison of time-resolved fluoroimmunoassay and ELISA in the detection of casein in foodstuffs

Abstract

Abstract With the aim of lowering the detection limit for casein in foods, three competitive assays are described: direct time-resolved fluoroimmunoassay (TR-FIA), using europium-conjugated antibody, indirect TR-FIA, using biotinylated antibody with europium-conjugated streptavidin and ELISA, using a HRP-conjugated secondary antibody. Food samples (instant potato, flour mix, packet soup, spice-mix) were analysed. Standard curve sensitivities in direct and indirect TR-FIAs did not differ significantly (p=0.097), but both TR-FIAs were considerably less sensitive (both p<0.0001) than ELISA (LOQs 1.3, 1.5 and < 1.0 mg kg−1, respectively). The precision and working analyte range was similar in all three methods. Casein content measured in food products was comparable, using the three assays and rocket immunoelectrophoresis. The TR-FIA approach provided no improvement over the ELISA. All three assays allowed quantification of casein in foodstuffs in the order of 1–1.5 mg kg−1, providing a basis for more rigorous validation and collaborative testing.