The third wave of test results announced by the FSA on Friday showed a small number of positive tests for horse DNA in meat products; however, that does not signal an end to the testing story. In fact the industry is gearing up for more.
RSSL has over ten years of experience in using DNA tests to detect species adulteration in food. The laboratory can identify meat from approximately 40 different species, fish from over 50 species and can also use DNA methods for food authenticity issues. As one of only a handful of laboratories with an established service, RSSL is gearing up to receive even more samples now that many retailers, manufacturers and food processors are introducing a vigorous due diligence testing programme. While many laboratories are trying to get to grips with introducing DNA methods to their portfolio of tests, RSSL is currently managing to offer a turnaround of 2 - 4 days for results.
"The recent findings of horse and pig DNA in beef products has clearly established a need for a broader range of testing which the industry has taken on board," notes Barbara Hirst of RSSL. "However, it must also be recognised that not all testing is the same. Methods have to be used appropriately, validated properly, and results have to be reported with scientific accuracy and with proper appreciation for the limitations of the test being used. We have maintained both the integrity of our testing along with a great service to our customers during this difficult time for the food industry. We are here to support all parties and ensure that the correct decisions are made by all stakeholders”.
RSSL uses two types of DNA analysis, depending on the specifics of the investigation. The first, known as real-time polymerase chain reaction (real-time PCR), involves using primer sequences (short lengths of DNA), which can pair with any complementary horse DNA found in the sample. The test then amplifies the specific DNA, like a biological photocopier (PCR), and a probe that is fluorescently labelled and specific to horse DNA releases the fluorescent tag and these copies can be counted in real time as they are produced.
The second DNA method is PCR restriction fragment length polymorphism (RFLP). Here, specific animal genes from within the sample are replicated many times, and the copies are 'cut' using restriction enzymes. The enzymes can be chosen to cut the DNA at points that give fragments specific to the species of interest. When these fragments are separated on a gel, the pattern of fragments can be compared against a reference sample to determine whether horse DNA (or DNA from any chosen species) is present.
Both of these methods work by replicating mitochondrial DNA, which is more highly conserved and more abundant in animals, than nuclear DNA. However, this also means that the methods cannot be used to quantify the amount of animal DNA found in samples.