Rocket immunoelectrophoresis and ELISA as complementary methods for the detection of casein in foods?

A rocket immunoelectrophoresis (RIE) method is described and compared with a commercial ELISA kit. Thirteen food products were selected from the categories sausage, rice pudding, fruit-ice, biscuit and baby-dinner. These had all tested negative for casein in a previous investigation using an older commercial ELISA kit. In the present study, using a more recent commercially developed ELISA kit and RIE, only three of the 13 products still tested negative for casein. However, the RIE detected levels of casein in ten of the remaining products, whereas the ELISA revealed the presence of casein only in the three products giving the highest levels of casein with RIE. Thus, the two methods both confirm the presence of casein when the levels in the samples are within the range of the detection limit for the ELISA method.