Importance of DNA in Seafood Authentication

If the material to be tested never contained cells or if no cell fragments remain in a product (e.g. they were removed through filtration, exposed to extremely high heat, or highly chemically processed), alternative methods to DNA are necessary, and may include chemical or other analytical tests.

Chemical Testing vs. DNA Testing

While chemical testing can provide information about the specific chemical components both in products that contain DNA and those that do not, chemical testing requires having an idea of what the product is. If you think you have salmon, you can run a chemical test to see if it’s salmon—the result is a yes or no. Chemical testing can also identify a known ingredient and its quantity. For example, you can test if the product contains caffeine and if so, how much. In addition, chemical testing is not highly specific, like DNA testing; many different organisms have identical chemical components. For instance, caffeine is found in numerous plants, such as coffee and tea, so it is not useful for species identification.

DNA testing provides the most definitive and specific identification available today. It can identify expected and unexpected adulterants, contaminants, substitutes, and allergens. DNA testing does not require a priori knowledge of what is supposed to be in the product. For instance, it can identify a completely unknown or mislabeled product; this is very important for testing samples from the marketplace that often are misbranded.

DNA Barcoding vs. NGS

DNA barcoding uses one standard genomic region (or gene sequence) to identify a species, similar to how UPC codes identify products when read by barcode scanners. It was developed to identify distinct groups of animals, such as fish versus chicken. NGS can also use the single gene region, but sequence it thousands of times from a single sample. It can also detect and identify allergens, fillers, and contaminants.

Both barcode and NGS methods can:

• Be used for living, fresh, or dried raw material with little or no processing;
• Place unknown or mislabeled species into general categories (tuna or salmon);
• Detect large amounts of adulterants (rice or soy); and
• Identify animal and plant DNA.

DNA barcoding and NGS differ in the use of primers. (A primer is a strand of short nucleic acid sequences, generally about 20 base pairs, that is the basis of DNA replication; it is explained in more detail it the next section.) DNA barcoding uses a single set of universal primers. While NSF’s NGS method uses validated universal primers and proprietary species-specific primers.

NSF uses a proprietary process called specific, targeted NGS that can identify more than 10,000 species of botanicals, animals, fungi, and bacteria in raw ingredients and finished products. These tests can differentiate between the most closely related and most difficult species to identify, including plant hybrids and complex mixtures. Batches can be sampled from any starting material.

NSF’s methods can also detect and identify allergens, fillers, and contaminants. For example, DNA Clean Screen identifies the presence of 11 common fillers and allergens at limits of detection as low as 50 picograms of DNA. These include wheat, soy, pea, corn starch, potato (maltodextrin), rice, peanut, almond, walnut, pecan, and hazelnut. NSF also offers two proprietary genetically modified organism (GMO) screens, which can be used on finished processed seafood products to verify label claims. These tests screen for the top 10 GMO species and the 10 most common GMO events or elements.

Both expected and unexpected contaminants, as well as fillers and allergens, are detected, whether they are in high and or very low abundance (down to a few molecules of DNA). NGS testing also provides relative ratios of DNA sequences to assess the extent of adulteration.