Seafood import brokers and food processing companies that import seafood for further processing utilize chemical taxonomy to verify the species of products their foreign suppliers sell to them.  This practice of establishing seafood authenticity is commonplace as a means of assuring that the importer receives the products it orders both for economic reasons, and to maintain the safety and quality of the importer’s finished products.

Detentions by U.S. FDA inspectors at ports of entry into the U.S. may now also require verification of species on many seafood products.  Marine species are commonly tested; species commonly of concern for fish speciation include Cod, Pollock, Haddock, Grouper, flatfish such as Halibut and Sole, Mackerel, Tuna, Snapper, and Dolphin (Mahi-Mahi); aquacultured species such as Catfish, Trout, and Tilapia may also be tested.  Chemical taxonomy can be applied to any finfish, shellfish, or crustacean species for which authentic standard material can be obtained.

The analytical technique, Isoelectric Focusing Gel Electrophoresis, separates species-characteristic sarcoplasmic proteins according to molecular weight on a gel plate placed between oppositely charged electrodes at low voltage.  Bands form as proteins of various molecular weights migrate differing distances on the gel.  Once stained and fixed, these bands present a “fingerprint” pattern characteristic to the species of fish tested.  In conventional electrophoresis, these bands may be broad; hence, there is a risk that two or more bands in close proximity may present as a single band and thereby confuse the identification of that species.

Isoelectric Focusing Electrophoresis (IEF) utilizes the tendency of protein molecules to carry a partial electrical charge as a way to allow much closer focusing and resolution of protein migration bands.  A pH differential is maintained between the electrodes, and a higher voltage is used in the separation.  The various proteins in the specimen migrate to the point at which electrical equilibrium is reached, forming much more sharply resolved migration bands compared to the conventional method.

After developing, the migration bands are coded and identified from a speciation database. Product samples must be frozen upon collection to –20 oC (-4 oF) and transported to the laboratory packed in dry ice in order to prevent denaturation of the proteins.  The failure to take this precaution may result in invalid test results.  It is also important to note that while most species can be identified using a standard pH gradient, in order to resolve close-lying protein bands for certain families such as Cod, Salmon, and Flatfishes (Gadidae, Salmonidae, and Pleuronectiformes, respectively), it is necessary to use a narrower pH gradient.

IEF is a critical tool for importers and food processors that seek to maintain honesty of the marketplace.  The risks that result from unverified product imports include use of lesser quality “substitutions” and loss of consumer confidence that can result from use of inferior product.  An additional risk lies in the potential consequences of inaccurate labeling of further-processed seafood products.

It is essential that both seafood import brokers and food processing facilities know that they are receiving product that meets their specifications.  As Official Method 980.16 of the Association of Official Analytical Chemists (AOAC), the Isoelectric Focusing Electrophoresis method provides a high degree of certainty to the process of fish species identification, and it is by far the most widely accepted method used for establishing seafood authenticity in the seafood import industry today.