The findings are reported in the August 14 print issue of Journal of Agricultural and Food Chemistry, a peer-reviewed journal of the American Chemical Society, the world's largest scientific society. They were the basis for widely publicized announcements by the Swedish National Food Administration and other European food administrations this spring.
The study reports that fried, oven-baked and deep-fried potato and cereal products contain high levels of acrylamide. Researchers at Stockholm University summarized evidence of acrylamide's presence in foods and performed a detailed analysis of acrylamide during heating.
Protein-rich foods, such as beef and chicken, produced only moderate levels of acrylamide when heated. Carbohydrate-rich foods, however, had high levels, with potato chips and French fries at the top of the list. Any item containing potato produced significant acrylamide upon heating in microwaves or conventional ovens. The study also found that more acrylamide forms as food is heated to higher temperatures.
"I would say that boiling at 100 degrees Celsius is the only safe cooking method," said Margareta Törnqvist, Ph.D., lead author of the paper. In potato-based foods, even cooking at a moderate temperature of 120 degrees Celsius began the process of acrylamide formation.
But Törnqvist is hesitant to promote mild cooking because it carries its own set of dangers -- namely food-borne diseases like Salmonella. Still, she said, the data support the conclusion that consumers should avoid overcooking, especially with potatoes. "It should also be noted that we have so far only studied carbohydrate-rich staple foods in the Western society," she said, "and we have not yet studied other types of diets."
Scientists originally thought the main exposure to acrylamide was through tobacco smoke; early studies suggested it formed during incomplete combustion of organic matter. When researchers found unusually high levels of acrylamide in Swedish subjects who were non-smokers and not exposed to other typical sources, the Stockholm group formed their heated-food hypothesis.
In an earlier study published in an ACS journal ("Acrylamide: A Cooking Carcinogen?" Chemical Research in Toxicology, 13 (6), 517-522, 2000), they fed rats fried animal feed for one or two months. The rats exhibited a higher level of acrylamide than a control group -- an increase similar in magnitude to the high levels observed in non-smoking humans.
After learning of the Stockholm University research, the Swedish government began testing acrylamide levels early this year and confirmed that many starch-rich foods contained high levels. This led to its announcement in April.
The Stockholm University study is the first to go through the peer-review process, and it bolsters the results made public by the Swedish National Food Administration and others. It also gives detailed information about the analytical methods used to measure acrylamide levels and the evidence for the identification of acrylamide in heated foods.
"This pilot study should be regarded as a first attempt to determine acrylamide in frequently consumed foodstuffs," the authors caution. It demonstrates the need for more studies concerning the presence of acrylamide in common foods.
-- Jason Gorss