Expert View: Why white powder can be a great danger
Nov 4 2008 by Our Correspondent, Huddersfield Daily Examiner
THE problem of melamine contamination of milk in China is the most recent example of the deliberate adulteration of food for commercial gain.
And once again it is analytical chemists who are at the forefront in the fight against unscrupulous profiteers.
At first glance melamine might seem to be a strange additive for food. In most British homes products made from melamine are more often found in the furniture than the fridge.
For instance, kitchen work surfaces are commonly made from melamine resin, a polymer which combines melamine and formaldehyde.
Melamine itself is a white crystalline powder, chemical name 1,3,5-triazine-2,4,6-triamine, and is not even very soluble.
So why is it added to milk?
The uses of melamine arise from an unusual aspect of its chemical composition; it is two-thirds nitrogen by weight. Its uses depend on that high proportion of nitrogen.
It is used as a fire-retardant in polymers because, on decomposing in fire, it releases nitrogen gas, which smothers the fire.
It is added to fertilisers as a source of nitrogen and now it seems it is illegally added to milk as a source of nitrogen to fool the tests of the milk’s quality.
Milk is analysed for constituents including fat, protein and carbohydrates. Protein is a measure of the quality of the milk and indicative of whether it has been diluted with water. Proteins are made up of chains of amino acids and a feature of amino acids is that they contain nitrogen.
The standard analytical test for protein has been around for a long time. In the 1880s the Carlsberg Brewery in Copenhagen wanted to be able to test the protein content of the grain they used to ensure the quality of the brewing process.
Their chief chemist, Johan Kjeldahl, came up with the solution. He realised that he could work out the amount of protein by simply measuring the nitrogen content. The method bears his name and is still widely used today.
With such a large proportion of nitrogen, although the cost of melamine is 10 times the cost of milk, adding even tiny amounts boosts the test result for the protein content of the milk and hence the price that is paid for the milk.
Addition of small amounts can boost the value of the milk by 100 times the cost of the melamine and allows someone, somewhere, along the supply chain from cow to home to dilute the milk.
But the problem is more serious than just one of greed and dishonesty.
Melamine can cause permanent damage to the body when ingested over a period of months. It, or possibly an impurity in the melamine, leads to the formation of crystals in the kidneys, which give rise to kidney stones and ultimately kidney damage.
Tragically, it is babies, fed with milk formula contaminated with melamine, who were most affected in the recent incidents in China, where at least four deaths have been reported.
This is not the first major incidence of melamine adulteration, which has been reported to have been a problem in China for some time.
Last year thousands of cats and dogs died in the US from pet food imported from China and contaminated with melamine.
While Kjeldahl analysis is carried out regularly on milk it is only now that authorities around the world are looking specifically for melamine and related compounds.
Since October the Food Standards Agency in Britain has enforced the testing of all dairy products from China that are sold here.
Traces of melamine have shown up in Britain in a novelty chocolate product which has now been recalled. Elsewhere, most reported cases of melamine contamination have been in South East Asia.
Perhaps more worryingly melamine has been found in other Chinese farm products such as eggs suggesting that the problem of contamination in China is more widespread than just milk.
In Britain we have been protected since the second half of the 19th century, when the first legislation was enacted and the public analysts were established to ensure food safety.
Before this the use of additives in food was common and sometimes dangerous. Examples included the use of poisonous lead compounds such as red lead to colour cheese and yellow lead chromate in custard powders and the poison strychnine used as an alternative to hops for bitterness in beer.
Nowadays the FSA, using results from analytical chemists, acts quickly to ensure that hazardous products are removed from the shelves.
This was shown in 2003 when the prohibited red dye Sudan I was found to have been added to imported chilli powder, used in products nationally.