By Janet Raloff
The process that imparts a golden hue to french fries and bread crusts also laces such foods with acrylamide, new studies indicate. That chemical causes cancer in laboratory animals.
Though acrylamide’s human toxicity remains unknown, the Food and Drug Administration this week announced plans to study ways to limit its formation in foods.
The first report of acrylamide in food occurred last April in Sweden. Since then, researchers in Europe have found it in a broad variety of baked, roasted, and fried fare, especially potatoes (SN: 8/24/02, p. 120: Available to subscribers at Cooking Up a Carcinogen.). The big puzzle has been how this substance, a building block of some plastics, forms during cooking.
One clue, four studies now show, is the so-called Maillard reaction, a flavor-enhancing browning that occurs when amino acids and sugars meet at high temperatures.
When scientists began searching for a source of food’s acrylamide, Maillard chemistry immediately came to mind, says Donald S. Mottram of the University of Reading in England. The reaction requires high temperatures and an amino acid. This amino acid could supply nitrogen, an ingredient of acrylamide, Mottram says. Indeed, he notes, the structure of the amino acid asparagine resembles acrylamide, and asparagine is potatoes’ primary unbound amino acid.
In the Oct. 3 Nature, Mottram’s team and another from the Nestlé Research Center in Lausanne, Switzerland, independently report cooking up acrylamide from asparagine heated with glucose, a simple sugar found in most foods. Addition of a little water tripled the acrylamide produced by heating just asparagine and glucose and yielded more than 1,700 times as much acrylamide as does heating asparagine by itself, the Nestlé group reports.
A week earlier, at an analytical chemistry symposium in Los Angeles sponsored by the professional group AOAC, two other laboratories also reported creating acrylamide from asparagine and glucose. One lab is at a Canadian government food-research agency in Ottawa, Ont., and the other is at Procter & Gamble in Cincinnati.
The Canadian team mixed pure asparagine with glucose in a ratio matching what’s typical in potatoes, then added water and cooked the soup for 10 minutes. No acrylamide appeared until cooking temperatures exceeded 120C and the sugar started browning, says James F. Lawrence, the agency’s director.
Acrylamide formation peaked at 175C. Even then, he notes, “the yield was low–a little under 1 percent” of the final mix. The scientists report a similar result in heated potatoes. Mottram says his July experiments revealed the same trend.
Since the unbound-asparagine content of potatoes can vary 10-fold, depending on variety, Lawrence posits that restaurants might someday select potatoes with low asparagine values for making french fries.
However, the Nestlé data reveal a more complicated picture. Richard H. Stadler and his colleagues tinkered with their acrylamide recipe by substituting three other common amino acids for the asparagine and swapping other sugars, including sucrose, for the glucose. Baked at 180C for 30 minutes, these alternative formulas also yielded significant amounts of acrylamide.
Nestlé’s findings challenge the notion of any “quick fix” for acrylamide in foods, says Michael Pariza of the University of Wisconsin–Madison, “because we’re not going to get rid of amino acids or sugars.” He adds, however, that his group is pursuing “some pretty good leads” toward short-circuiting acrylamide’s formation from those ingredients.
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