Detection of the presence of soya protein in milk powder by sodium dodecyl sulfate capillary electrophoresis

Two different commercial kits for sodium dodecyl sulfate capillary electrophoresis (SDS-CE) were evaluated for the detection of the presence of soya protein in milk powder. The results obtained showed that SDS-CE allowed the separation of the basic subunits of glycinin and the alpha and alpha' subunits of beta-conglycinin from the main milk protein peaks. However, a detection limit lower than 10% (w/w) of soya protein in total protein could not be achieved. The use of a tetraborate-EDTA sample treatment minimized interferences from milk proteins, allowing the detection of at least 1% (w/w) of soya protein in total protein. The addition of soya protein hydrolysates could not be determined using SDS-CE.