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New meat test

Fabian Schmidt / ai March 4, 2013

Food labs usually only check meat for what they suspect might be in it - a lot could pass unnoticed. Now, German researchers have come up with a single test for meat products to identify as many as 50 different animals.

Hands holding beef and horse salami side by side
Beef and horse salamiImage: DW/F. Schmidt

Even if food laboratories do a good job, they can only look for what they might suspect is in a product. If there's some faulty ingredient that's off the radar, this most likely will pass the tests.

But now, researchers at the Fraunhofer Institute for Molecular Biology and Ecology in Schmallenberg have developed a single test for tracing about 50 different animals.

For Matthias Kotthoff, dealing with food is more a calling than just a job. Already before his nutritional science and molecular biology studies, he finished training as a chef. It's pure routine when he picks up and inspects beef or horse sausage.

"We have a typical salami smell here. In case of horse salami, the smell is a bit more acidic," Kotthoff said. "This might be to do with the way it's been prepared, as the two sausages come from two different butchers," he added.

"Both of them actually smell quite tasty," he said, adding with a smile that even though he is a food inspector by profession, he of course cannot distinguish a meat by its smell alone. Horse salami usually is slightly darker than beef - but the color is not always reliable.

Probes enter machine in DNA lab
Minute portions of DNA get isolated and eventually reveal where the meat originatedImage: DW/F. Schmidt

"Unless you don't have two sausages next to each other, it's very difficult to tell."

DNA analysis

Since neither eyes nor nose can do the job, food testers identify it through DNA testing. His assistant cuts a minute sample from the sausage. All instruments must be sterile, as even a tiny bit of foreign genetic material could compromise the result.

The thin sausage slice is then shock frozen by being covered with liquid nitrogen. The frozen meat is then pulverized, and a tiny sample is taken for the DNA test. In a test tube, the assistant adds an enzymatic liquid to the powder, which breaks down the cell walls and releases the DNA from cell nucleus.

Fractions of genes

In order to identify the animal for that meat, Kotthoff doesn't need the entire DNA, merely a small sample. This fraction of the DNA he then multiplies by several billion through a special process. What he's after is the Cytochrome b gene, which is responsible for the color of the cells.

It's a gene that all animals share, but with minute differences. "There's a different in length in the fraction of the gene sequence," Kotthoff reveals. And that's what helps in distinguishing the meat. He marks the fraction of the gene with color at the beginning and end.

Two chunks of meat
Beef, horse, or perhaps even crocodile?Image: DW/F. Schmidt

Then yet another machine measures the color markings with a sensor. Depending on the distance between color markings, Kotthoff can tell which animal that particular gene sequence belongs to. In a graph on his computer screen, the sensor's generates peaks in a graph that Kotthoff uses to assign the meat to a certain animal species.

Devil in the detail

So far, the list contains 50 animals, among them horse, sheep and cow, or poultry like chicken, duck or ostrich. The method also works for fish. "We even have a number of exotic animals on our list, like crocodile or kangaroo," Kotthoff said.

The greatest advantage of the new technology is that everything can be traced. The disadvantage: the smallest amount of contamination can be a problem. If the scientist, for instance, talks he's testing, the smallest particles of saliva "already contain enough DNA for it to be identified," he said.

"So if the butcher sneezes or maybe accidentally cuts himself, it would just be a matter of time before the headlines read 'Traces of Human Meat found,'" he warned.

That means that even traces of horsemeat could be found in beef if both pieces of meat merely touched each other in storage, or were processed with the same machines.

Even the DNA traced doesn't provide a clear picture of the actual amount of that type of meat in the sample. And not all meat is the same. Meat containing nerve cells, for instance, hold a million times more cells - and therefore also DNA molecules - than fatty tissue.

So if a sausage contains one gram of beef nerve mixed with one kilo of pork fat, lab results would suggest to the untrained eye that the sausage is, in fact, mostly beef.