The Maillard reaction accounts for acrylamide in crisps. Credit: © DigitalVision

Acrylamide, a compound that causes cancer symptoms in animals, is formed during frying and baking, two studies now show.

The discovery solves a mystery that had caused public alarm. In April a Swedish study found the chemical in crisps and biscuits, but not raw food, at levels higher than the World Health Organisation (WHO) recommends for drinking water1.

"I haven't known as much interest in a topic in many years," says Don Mottram, who studies food chemistry at the University of Reading, UK. Not knowing where the chemical was coming from was "a very big problem", he explains.

Baked bread tastes better than raw dough, and fried chips are tastier than boiled, because of the Maillard reaction. As long as there's sugar around, high temperature breaks proteins down to give food more flavour and a golden brown colour.

The Maillard reaction also produces acrylamide, Mottram has found, as has Richard Stadler of the Nestlé Research Centre in Lausanne, Switzerland, in independent experiments2,3. Potatoes and some cereals contain large amounts of the amino acid asparagine, which is similar to acrylamide. In the lab, heating asparagine with sugar at 185 °C turns much of it into acrylamide, Motram and Stadler have found.

"During cooking, many complex chemical reactions take place," says Stadler: other amino acids change their form repeatedly, also producing acrylamide. More tests are needed on different types of food to see how acrylamide forms, he says, and to understand the effects of different cooking techniques.

Exposing more of a food to higher temperatures, as in thin potato crisps, generates more acrylamide. So too does cooking food for longer. No acrylamide has been found so far in boiled foods, probably because of their lower cooking temperature.

Hot topic

In rats and fruitflies, acrylamide causes cancerous changes, at concentrations 1,000 times higher than those found an average diet. There is no direct evidence for acrylamide having a similar impact on humans, but the International Agency for Research on Cancer nevertheless classified it as "probably carcinogenic" in 19944.

Rats don't eat heated food. But as humans have been doing so for thousands of years, we may be more tolerant to acrylamide, Mottram suggests. Obesity, diabetes and a lack of fruit and vegetables in Western diets are more serious health threats than acrylamide, he adds.

The mechanism is just one of many missing points Jorgen Schleudt , WHO

Finding the mechanism at work is important, but still just "one of many missing points", says Jorgen Schleudt, head of WHO's food-safety programme. He is calling for more research into the effects of acrylamide on humans.

Indeed, next week the United Nations Food and Agriculture Organization and WHO are launching a web-based network to coordinate acrylamide research. It should encourage a "global exchange of information", Schleudt explains.

raised much concern, but... Nature419, 449 - 450 (03 Oct 2002) DOI: 10.1038/