Two studies now show that the compound, acrylamide, that causes cancer symptoms in animals, is formed during frying and baking of certain foods.
“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.
The high temperatures involved in baking bread and frying chips cause the proteins in these foods to break down, giving them more flavour and a golden brown colour. This additional flavour is a result of the Maillard reaction.
Mottram has found, as has Richard Stadler of the Nestle Research Centre in Lausanne, Switzerland, through independent experiments that the Maillard reaction also produces acrylamide. Potatoes and some cereals contain large amounts of the amino acid asparagine, which is similar to acrylamide. Motram and Stadler have found that in the lab, heating asparagine with sugar at 185 degrees Celcius turns much of it into acrylamide.
“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.
According to researchers, more acrylamide is generated when more of a food is exposed to high temperatures, as in thin potato crisps. So too does cooking food for longer. Acrylamide has not yet been found in boiled foods, probably because of their lower cooking temperature.
During laboratory experiments it was found that acrylamide causes cancerous changes in rats and fruitflies, at concentrations 1,000 times higher than those found in an average diet. Although there is no direct evidence for acrylamide having a similar impact on humans, the International Agency for Research on Cancer nevertheless classified it as “probably carcinogenic” in 1994.
Rats however don’t eat heated food. Humans may be more tolerant to acrylamide because they have been eating heated foods for thousands of years, Mottram suggests. Obesity, diabetes and a lack of fruit and vegetables in Western diets are more serious health threats than acrylamide, he adds.
Finding the mechanism at work is important, but still just “one of many missing points”, says Jorgen Schleudt, head of WHO’s food-safety program. He is calling for more research into the effects of acrylamide on humans.
Indeed, next week the United Nations Food and Agriculture Organisation and WHO are launching a web-based network to coordinate acrylamide research. It should encourage a “global exchange of information”, Schleudt explains.
(Source: British Journal of Cancer)