Too much nitrogen

19 September 2008

One thing that was bugging me from the news today was why anyone would try to adulterate food with melamine - a material that makes hard-to-break plates but which needs to be kept out of food itself. Given that melamine has turned up in a number of contaminated food scandals, particularly pet food, a poison seemed an odd choice as an adulterant.

The news reports explained that melamine makes it look as though there is more protein in the food being tested. But melamine itself is no protein. It's not even close. How come it comes up positive?

The answer lies in the test itself. Because the process has to be carried out so often, you don't go looking for protein, or the amino acids that join up to form it. The test works on the basis that carbohydrates and fats don't have a lot of nitrogen in them: they are generally pretty much all carbon, hydrogen and oxygen. The protein test simply uses nitrogen - there is at least one atom of nitrogen in every amino acid - as a proxy for protein content. And melamine is stuffed full of nitrogen - about five to six times as much per molecule than an amino acid.

Short of lacing the food with cyanide, urea or some ammonium salt, you couldn't get a more evil or effective "protein substitute". It's only when you perform a more sophisticated test that melamine turns up. But, can such a test be administered as cheaply as the flawed nitrogen-content check?