Collaborative study on the detection of caseinate and soya protein isolate in meat products

A collaborative study on the detection of caseinate and soya protein isolate in meat products was carried out by 11 laboratories in the Netherlands. The aim of this study was to propose a simple and reliable method suitable to be adopted as an Official Method of Analysis for the Dutch Food Law on meat and meat products. After preliminary investigations, it was decided to select the polyacrylamide electrophoresis in rods or slab gels together with the double immunodiffusion technique as the most suitable methods for the purpose. Subsequently, these methods were tested collaboratively with ten different meat products covering a wide variety of meats such as smoked sausage (n = 2), shoulder (n = 2) and raw fermented sausage (n = 2). The products contained known amounts of caseinate and soya protein isolate ranging from 0 to 2.0 p. 100. For caseinate, the immunodiffusion technique provided results, that were correct in 80 p. 100 of all cases whereas 79 p. 100 correct results were obtained with the electrophoretic procedure. The percentage of false positive results was 13 p. 100 and 9 p. 100 respectively, whereas the percentage of fault negative results was 7 p. 100 for the immunological and 12 p. 100 for the electrophoretic procedure. For soya protein isolate, 81 p. 100 of all results were correct as far as the double immunodiffusion method is concerned. No false positives were found, but in 19 p. 100 of the cases the addition was not detected. For the electrophoretic procedure, the percentage of correct results was 74 p. 100; 4 p. 100 false positives and 22 p. 100 unjustly negative results were reported. Soya protein was not detectable in sterilized products (heating temperatures higher than 100 °C) whereas for the raw and mildly heated products 100 p. 100 and 87 p. 100 of the results were correct for the serological and electrophoretic procedures, respectively. It was concluded, that the percentage of false positive results in detecting caseinate is considerably reduced when both procedures are applied to the same sample. The application of both the electrophoretic and the double immunodiffusion procedure for the detection of caséine and caseinates in meat products was therefore recommended as an Official Dutch Method. The detection of soya protein isolate in meat products by immunodiffusion gives more satisfactory results than the electrophoretic method as far as the meat product is not heated to temperatures higher than 100 °C.