Structure of Chinese Milk Contaminant Determined

The crystal structure of melamine cyanurate, the chemical thought to be the culprit in the 2008 contamination of milk that sickened some 300,000 Chinese infants, has been described by scientists in the U.K. The publication, which corrects a previous report on the crystal structure, may allow the design of better tests to detect melamine in food products, says the first author of the paper, published in the journal CrystEngComm.

“This work highlights the need for more sophisticated methods to determine protein content,” says Timothy J. Prior, DPhil, a lecturer in inorganic chemistry at the University of Hull. “At present the simple test used to determine nitrogen content, which is then used as a measure of protein content, can be tricked by adding nitrogen-rich molecules such as melamine. If more advanced tests for protein content not based on total nitrogen content were available, adding melamine would be of no advantage to unscrupulous suppliers.”

In 2008, six children died and many thousands were sickened when melamine was added to a powdered milk formula in China. Melamine, an industrial chemical used in the manufacture of plastics, is high in nitrogen content, and can therefore be used to deceive Kjeldahl and other assays that use nitrogen as a surrogate to determine protein content in foods.

Identification of the crystal structure of melamine in combination with cyanuric acid offers a possible route to designing better tests, Dr. Prior suggests in an email to Food Quality & Safety.

“There is already a large body of work concerned with detecting melamine, but crucially no method currently exists that is cheap, portable, and works to an appropriate detection limit,” he says. “Our work should help in designing the next generation of sensors for melamine because we now have precise information about how melamine sticks to cyanuric acid to form very stable (very insoluble) crystals. If we could design a molecule with the kind of ‘pocket’ we have identified here that changed in some measurable way when melamine was added, we would have the basis of a sensor.”

The work that determined the melamine cyanurate crystal structure was a side discovery on a different project and is not Dr. Prior’s main focus. “However, my group has already done some work into the detection of melamine in collaboration with a colleague who is an electrochemist, and we hope to publish this soon,” he says.