Identification of fish species after cooking by SDS-PAGE and urea IEF: A collaborative study

A collaborative study, to validate the use of SDS-PAGE and urea IEF, for th e identification of fish species after cooking has been performed by nine l aboratories. By following optimized standard operation procedures, 10 comme rcially important species (Atlantic salmon, sea trout, rainbow trout, turbo t, Alaska pollock, pollack, pink salmon, Arctic char, chum salmon, and New Zealand hake) had to be identified by comparison with 22 reference samples. Some differences in the recoveries of proteins from cooked fish flesh were noted between the urea and the SDS extraction procedures used. Generally, the urea extraction procedure appears to be less efficient than the SDS ext raction for protein solubilization. Except for some species belonging to th e Salmonidae family (Salmo, Oncorhynchus), both of the analytical technique s tested (urea IEF, SDS-PAGE) enabled identification of the species of the samples to be established. With urea IEF, two laboratories could not differ entiate Salmo salar from Salmo trutta. The same difficulties were noted for differentiation between Oncorhynchus gorbuscha and Oncorhynchus keta sampl es. With SDS-PAGE, three laboratories had some difficulties in identifying the S. trutta samples. However, in the contrast with the previous technique , SDS-PAGE allows the characterization of most of the Oncorhynchus species tested. Only Oncorhynchus mykiss was not clearly recognized by one laborato ry. Therefore, SDS-PAGE (Excel gel homogeneous 15%) appears to be better fo r the identification, after cooking, of fish such as the tuna and salmon sp ecies which are characterized by neutral and basic protein bands, and urea IEF (CleanGel) is better for the gadoid species, which are characterized by acid protein bands (parvalbumins). Nevertheless, in contentious cases it i s preferable to use both analytical methods.