Isoelectric focusing of sarcoplasmic proteins to distinguish swordfish, blue marlin and Mediterranean spearfish

In the present study we show that the method of isoelectric focusing (IEF) is a simple and reliable one for detecting the fraudulent substitution of cold-smoked fillets of swordfish (Xiphias gladius) with those of lower value blue marlin (Makaira mazara) and for detecting substitution of blue marlin steaks with those of Mediterranean spearfish (Tetrapturus belone). The cold smoking process does not alter the sarcoplasmic proteins of the fish species, so cold smoked fillets of the species investigated can be identified in the same was as fresh and frozen samples.