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Acrylamide
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The chemical compound acrylamide ( acrylic amide) has the chemical formula C3H5NO. Its IUPAC name is 2-propenamide. It is a white odourless crystalline solid, soluble in water, ethanol, ether and chloroform. Acrylamide is incompatible with acids, bases, oxidizing agents, iron and iron salts. It decomposes non-thermally to form ammonia, and thermal decomposition produces carbon monoxide, carbon dioxide, and oxides of nitrogen.
Acrylamide is prepared on an industrial scale by the hydrolysis of acrylonitrile by nitrile hydratase.
Most acrylamide is used to synthesize polyacrylamides, which find many uses as water-soluble thickeners.
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Encyclopedia
The chemical compound acrylamide ( acrylic amide) has the chemical formula C3H5NO. Its IUPAC name is 2-propenamide. It is a white odourless crystalline solid, soluble in water, ethanol, ether and chloroform. Acrylamide is incompatible with acids, bases, oxidizing agents, iron and iron salts. It decomposes non-thermally to form ammonia, and thermal decomposition produces carbon monoxide, carbon dioxide, and oxides of nitrogen.
Acrylamide is prepared on an industrial scale by the hydrolysis of acrylonitrile by nitrile hydratase.
Most acrylamide is used to synthesize polyacrylamides, which find many uses as water-soluble thickeners. These include use in wastewater treatment, gel electrophoresis (SDS-PAGE), papermaking, ore processing, and the manufacture of permanent press fabrics. Some acrylamide is used in the manufacture of dyes and the manufacture of other monomers.
Acrylamide was accidentally discovered in foods in April 2002 by scientists in Sweden when they found large amounts of the chemical in starchy foods, such as potato chips, French fries and bread that had been heated (production of acrylamide in the heating process was shown to be temperature-dependent). It was not found in food that had been boiled nor in foods that were not heated.
In February 2009, Health Canada announced to recommend placing acrylamide, which can be found in French fries, potato chips and other processed foods, on the country's toxic substances list as a part of an ongoing review by the government of nearly two hundred potentially harmful substances in widespread commercial use. It can also be detected in breakfast cereals, pastries, cookies, breads, rolls, toast, cocoa products and coffee, although at levels far below those in fried potato products. According to Health Canada, the toxic listing was based on the "carcinogenic potential" of acrylamide and the lack of an adequate safety margin at current exposures for causing reproductive and developmental harm during fetal and early life development.
Laboratory use
Polyacrylamide was first used in a laboratory setting in the early 1950s. In 1959, two independent groups published papers; , and ) on the use of polyacrylamide gel electrophoresis to separate charged molecules. The technique is widely accepted today, and is still an extremely common protocol in molecular biology labs.
Acrylamide also has many other uses in the modern molecular biology laboratory, including the use of linear polyacrylamide (LPA) as a carrier which aids in the precipitation of small amounts of DNA. Many laboratory supply companies sell LPA as a commercial product for just this use.
Prepared foods
Acrylamide levels appear to rise as food is heated for longer periods of time. Though researchers are still unsure of the precise mechanisms by which acrylamide forms in foods, many believe it is a byproduct of the Maillard reaction. In fried or baked goods, acrylamide may be produced by the reaction between asparagine and reducing sugars (fructose, glucose, etc.) or reactive carbonyls at temperatures above 120 °C (248 °F).
A study by the U.S. Food and Drug Administration (FDA) proposed a mechanism that involves asparagine, which, when heated in the presence of glucose, forms acrylamide.
Based on current stage of knowledge, acrylamide is a natural byproduct that forms when certain carbohydrate-rich foods are fried, baked, or roasted at high temperatures above 120 °C. Acrylamide causes cancer in rats when administered orally in high dose experiments, increasing tumors in the nervous system, oral cavity peritoneum, thyroid gland, mammary gland, uterus, and clitoris. There is a margin of 900-fold between human exposure to acrylamide in the diet and the dose that gave cancer to 10% of rats.
Raw, dried, and pickled foods
Acrylamide in olives, prunes, and dried pears develops through another process. Genetics professor Joe Cummins suggests a link between acrylamide and herbicides such as glyphosate (Roundup), citing studies which show that heat and light can decompose polyacrylamide, the thickening agent used in commercial herbicides, into acrylamide.
Tobacco
Cigarette smoking is also a major acrylamide source.
Beverages
Estimates for the proportion of acrylamide in adults’ diet coming from the consumption of coffee range from twenty to forty percent; prune juice has a high concentration of acrylamide, though adults consume it in far smaller quantities.
Cooking methods that affect acrylamide production
Acrylamide cannot be created by boiling, and very few uncooked foods contain any detectable amounts.
Browning during baking, frying or deep-frying will produce acrylamide, and over-cooking foods may produce large amounts of acrylamide. Acrylamides can also be created during microwaving. The FDA has analyzed a variety of U.S. food products for levels of acrylamide since 2002, these results can be found .
Reduction of acrylamide formation
The Confederation of the Food and Drink Industries in the EU has published a number of brochures to help people reduce the amount of acrylamide formed in their food. They offer a general acrylamide as well as publications specific to reducing the acrylamide in , , , , and .
Storage
In the case of potatoes, for instance, the storage temperature should not drop below 8 °C (46 °F). When the temperature is as low as 4 °C (39 °F) the fructose content rises sharply, so that the acrylamide formation during baking or deep-frying will be higher.
Raw material
New varieties of potatoes that produce less or no acrylamide are being bred.
Production methods
In many cases, it is advisable to lower the maximum temperature during baking. Also, new production methods such as vacuum frying may lower the acrylamide formation.
When silicone is used as a foam inhibitor in deep-frying fats in the food industry, the acrylamide content is doubled.
Recipe formulation
Asparaginase, a naturally-occurring enzyme, can be added to bread or potato mixtures to reduce formation of acrylamide during cooking.
Published articles on the potential health risks to humans
Inhaled, absorbed or ingested acrylamide
There is evidence that exposure to large doses can cause damage to the male reproductive glands. Direct exposure to pure acrylamide by inhalation, skin absorption, or eye contact irritates the exposed mucous membranes, e.g., the nose, and can also cause sweating, urinary incontinence, nausea, myalgia, speech disorders, numbness, paresthesia, and weakened legs and hands. In addition, the acrylamide monomer is a potent neurotoxin, causing the disassembly or rearrangement of intermediate filaments. Ingested acrylamide is metabolised to a chemically reactive epoxide, glycidamide.
British Journal of Cancer
In 2003, the British Journal of Cancer published an article titled
The article was based on a study led by L A Mucci that reanalysed a population-based Swedish case-control study encompassing cases with cancer of the large bowel, bladder and kidney, and 538 healthy controls. Researchers assessed the impact of dietary acrylamide “by linking extensive food frequency data with acrylamide levels in certain food items recorded by the Swedish National Food Administration. Unconditional logistic regression was used to estimate odds ratios, adjusting for potential confounders.” Dr. Mucci’s group “found consistently a lack of an excess risk, or any convincing trend, of cancer of the bowel, bladder, or kidney in high consumers of 14 different food items with a high (range 300-1200 µg kg-1) or moderate (range 30-299 µg kg-1) acrylamide content.”
Dr. Mucci’s group was surprised by one finding, writing “Unexpectedly, an inverse trend was found for large bowel cancer (P for trend 0.01) with a 40% reduced risk in the highest compared to lowest quartile.” Sounding a note of cautious optimism, the article concludes “We found reassuring evidence that dietary exposure to acrylamide in amounts typically ingested by Swedish adults in certain foods has no measurable impact on risk of three major types of cancer. It should be noted, however, that relation of risk to the acrylamide content of all foods could not be studied.”
Cancer, epidemiology, biomarkers, and prevention
A number of studies pertaining to acrylamide have appeared in various issues of Cancer, Epidemiology, Biomarkers & Prevention. Two of the more germane are and
The first study was led by Dr. Janneke G. Hogervorst and included 62,573 women, aged 55-69 years. The acrylamide intake of subcohort members and cases was assessed with a food frequency questionnaire and was based on chemical analysis of all relevant Dutch foods. Subgroup analyses were done for never-smokers to eliminate the influence of smoking, an important source of acrylamide.
After 11.3 years of follow-up, the researchers observed 327, 300, and 1,835 cases of endometrial, ovarian, and breast cancer, respectively. Hogervorst’s group concluded that his subjects faced “increased risks of postmenopausal endometrial and ovarian cancer with increasing dietary acrylamide intake, particularly among never-smokers. Risk of breast cancer was not associated with acrylamide intake.”
The second study was led by Dr. Uwe Fuhr and sought to evaluate the how much of the acrylamide humans eat is absorbed into the body. The study consisted of six young healthy volunteers consuming a meal containing 0.94 mg of acrylamide and then providing urine was for up to 72 hours thereafter. Fuhr’s group concluded that “most of the acrylamide ingested with food is absorbed in humans.”
Heat-generated food toxicants (HEATOX)
The Heat-generated Food Toxicants () Project was a “multidisciplinary research project involving 24 partners in 14 countries.” It ran from late 2003 to early 2007. Its objectives were to “estimate health risks that may be associated with hazardous compounds in heat-treated food[, and] find cooking/processing methods which minimise the amounts of these compounds, thereby providing safe, nutritious and high-quality food-stuffs.” Its final report is located .
Unlike more academic studies, HEATOX sought also to provide consumers with advice on how to lower their intake of acrylamide. The group recommends that national authorities highlight the following:
Potatoes low in sugar
- Low sugar potato varieties
- Maintenance of suitable storage temperature during the supply chain
- Low sugar levels in prefabricated potato products for domestic frying.
Best frying temperature
- Frying temperature in the range 145 to 170 °C (300 to 350 °F) for deep frying potatoes.
- Clear and accurate cooking instruction on the package of pre-fried products.
- Clear and accurate instruction for fryers for domestic use.
Golden, not brown!
- French fries and roast potatoes cooked to a golden-yellow rather than golden-brown colour.
- Bread toasted to the lightest colour acceptable.
International Journal of Cancer
In March, 2003, the International Journal of Cancer published an article with the forthright title The article reported on a study conducted between 1991 – 2000 in Italy and Switzerland that analyzed the risk of cancer of the oral cavity and pharynx, esophagus, larynx, large bowel, breast and ovaries. It was led by Claudio Pelucchi whose team found “reassuring evidence for the lack of an important association between consumption of fried/baked potatoes and cancer risk.”
More recently, in January, 2008, one of the HEATOX members published The article addresses a study led by Dr. PT Olesen of the National Food Institute, Technical University of Denmark. The abstract to the study states “So far, epidemiological studies have not shown any association between human cancer risk and dietary exposure to acrylamide. The purpose of this study was to conduct a nested case control study within a prospective cohort study on the association between breast cancer and exposure to acrylamide using biomarkers.” The study found that “[a]fter adjustment for smoking behavior. . . a positive association was seen between acrylamide-hemoglobin levels and estrogen receptor positive breast cancer. . . . A weak association between glycidamide hemoglobin levels and incidence of estrogen receptor positive breast cancer was also found, this association, however, entirely disappeared when acrylamide and glycidamide hemoglobin levels were mutually adjusted.”
Journal of the American Medical Association
The March 15, 2005 issue of the Journal of the American Medical Association (JAMA) contained an article titled written by Lorelei A. Mucci, ScD, MPH. The study cohort consisted of 43,404 Swedish women in the Women’s Lifestyle and Health Cohort. The women’s greatest single source of acrylamide was from coffee (54% of intake), fried potatoes (12% of intake), and crisp bread (9% of intake).
The study concluded “Compared with the lowest quintile of acrylamide intake, there was no significantly increased risk of breast cancer in the higher quintiles and no evidence of a linear dose response. For quintile 5 compared with quintile 1, the relative risk was 1.19 (95% confidence interval, 0.91-1.55). Furthermore, there was no association between breast cancer risk and higher intake of any specific foods including coffee, fried potatoes, and crisp bread.”
World Health Organization
The World Health Organization WHO has set up a for information about acrylamide that includes database of researchers/data providers; References for research published elsewhere; Information updates about the current status of research efforts; and updates on information relevant to the health risk of acrylamide in food.
One question the site’s FAQ addresses is whether there can be an acceptable level of acrylamide in food. The WHO states that “Acrylamide belongs to the group of chemicals thought to have no reliably identifiable ‘threshold’ of effects, meaning that very low concentrations will also result in very low risks, but not in zero risk: some risk is always present when the chemical is ingested. However, for these carcinogens, risk is thought to increase with increasing exposure.
Very low risks (even of cancer), such as those that are less than one in one million, are considered to be acceptable to some consumers. To others this is unacceptable. The important pre-requisite for any decision is, however a clear picture of the nature and level of the risk, as well as the potential for lowering this level. This clear picture does not exist for acrylamide at present.”
Safe levels of acrylamide
In June 2002, the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) issued a report about the health implications of acrylamide in food. After study, the Consultation concluded that the no observed adverse effect level (NOAEL) for acrylamide neuropathy is 0.5 mg/kg body weight/day and the NOAEL for fertility changes is four times higher than for peripheral neuropathy. The study continued, “On the basis of current knowledge, controlling for peripheral neuropathy is expected to control for effects on fertility. The estimated average chronic human dietary intake is in the order of 1 µg/kg body weight/day. This provides a margin between exposure and the NOAEL of 500.”
Hence, a woman weighing 132 pounds (60 kg) could safely consume 30 mg of acrylamide daily; a man weighing 180 pounds (82 kg), about 41 mg; a child weighing 40 pounds (18 kg), 9 mg.
Referring to the chart below for the amount of acrylamide in foods, in a single day, the child can eat 13 kg (28 lb) of French fried potatoes, the woman can drink 86 kg (~86 L, or 23 US gal) of prune juice, and the man can eat 29 kg (63 lb) of oven baked potatoes, and each of them will have ingested less than 50 percent of the NOAEL of acrylamide.
| Food | AA concentration
(µg/kg) | Portion size
(g) | AA per portion
(µg) |
|---|
| French fries (OB) | 698 | 70 | 48.8 | | Prune juice | 174 | 140 | 24.4 | | French fries (RF) | 334 | 70 | 23.3 | | Postum | 93 | 240 | 22.3 | | Potato chips | 546 | 30 | 16.4 | | Canned black olives | 550 | 15 | 8.2 | | Breakfast cereal | 131 | 55 | 7.3 | | Brewed coffee | 8.5 | 240 | 3.2 |
(adapted from , page 17)
Public awareness
On April 24, 2002, the Swedish National Food Administration (Livsmedelsverket) announced that acrylamide can be found in baked and fried starchy foods, such as potato chips, breads and cookies. Concern was raised mainly because of the carcinogenic effects of acrylamide. This was followed by a strong but short-lived interest from the press. On 2005-08-26, California attorney general Bill Lockyer filed a lawsuit against top makers of french fries and potato chips to warn consumers of the potential risk from consuming acrylamide. The lawsuit was settled on 2008-08-01 with the food producers agreeing to cut acrylamide levels in half.
In 2007, more than 100 articles were written about acrylamide, according to Nexis and Factiva, including pieces in the LA Times, the Boston Globe , the Guardian, and the Wall Street Journal, among others. Of these articles, nearly half appeared in November and December, when people were frying potatoes for latkes, and roasting pigs and turkeys.
On August 1, 2008, four food manufacturers - H.J. Heinz Co., Frito-Lay, Kettle Foods Inc., and Lance Inc. - agreed to reduce levels of acrylamide in their products (such as potato chips and French fries) over a three-year period and pay a combined $3 million in fines as a settlement with the California attorney general's office. California had sued these four companies in 2005, alleging they violated a state requirement that companies post warning labels on products with carcinogens.
See also
External links
- Acrylamide and Food
- IARC Monograph ""
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