Acrylamide (or acrylicamide) is an organic compound with the chemical formula CH2=CHC(O)NH2. It is a white odorless solid, soluble in water and several organic solvents. From the chemistry perspective, acrylamide is a vinyl-substituted primary amide (CONH2). It is produced industrially mainly as a precursor to polyacrylamides, which find many uses as water-soluble thickeners and flocculation agents. Acrylamide forms in burnt areas of food, particularly starchy foods like potatoes, when cooked with high heat, above 120 °C (248 °F).[6][7][8][9] Acrylamide is highly toxic, linked to cancer in animal testing[7][8][9] though not likely to be carcinogenic for humans,[10] but its main derivative polyacrylamide is nontoxic. The possibility that this innocuous polymer contains traces of its hazardous precursor has long attracted attention. Because acrylamide is volatile and hazardous, it is mainly handled as an aqueous solution.
Production
Acrylamide can be prepared by the hydration of acrylonitrile:
CH2=CHCN + H2O → CH2=CHC(O)NH2
This reaction is catalyzed by sulfuric acid, various metal salts, and the enzyme nitrile hydratase. In 2008, an estimated 750,000,000 kg of polyacrylamide were produced, mainly using the enzymatic route.[11]
Uses
Proteins of the erythrocyte separated by use of polyacrylamide gels (SDS-PAGE)
The majority of acrylamide is used to manufacture various polymers, especially polyacrylamide. This water-soluble polymer, which has very low toxicity, is widely used as thickener and flocculating agent. These functions are valuable in the purification of drinking water, corrosion inhibition, mineral extraction, and paper making. Polyacrylamide gels are routinely used in medicine and biochemistry for purification and assays.[11]
Toxicity and carcinogenicity
N-(D-glucos-1-yl)-L-asparagine, precursor to acrylamide in cooked food[12]
Acrylamide can arise in some cooked foods via a series of steps by the reaction of the amino acid asparagine and glucose. This condensation, one of the Maillard reactions, followed by dehydrogenation produces N-(D-glucos-1-yl)-L-asparagine, which upon pyrolysis generates some acrylamide.
The discovery in 2002 that some cooked foods contain acrylamide attracted significant attention to its possible biological effects.[11]IARC, NTP, and the EPA have classified it as a probable carcinogen. Although epidemiological studies (as of 2019) suggest that dietary acrylamide consumption does not significantly increase people's risk of developing cancer,[10] genomic analysis has revealed widespread contribution of acrylamide exposure to human carcinogenesis.[13]
Europe
According to the EFSA, the main toxicity risks of acrylamide are "Neurotoxicity, adverse effects on male reproduction, developmental toxicity and carcinogenicity".[14][15] However, according to their research, there is no concern on non-neoplastic effects. Furthermore, while the relation between consumption of acrylamide and cancer in rats and mice has been shown, it is still unclear whether acrylamide consumption has an effect on the risk of developing cancer in humans, and existing epidemiological studies in humans are very limited and do not show any relation between acrylamide and cancer in humans.[14][16] Food industry workers exposed to twice the average level of acrylamide do not exhibit higher cancer rates.[14]
HEATOX (heat-generated food toxicants) study in Europe
The Heat-generated Food Toxicants (HEATOX) Project was a European Commission-funded multidisciplinary research project running 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 to] find cooking/processing methods that minimize the amounts of these compounds, thereby providing safe, nutritious, and high-quality food-stuffs."[17][18] It found that "the evidence of acrylamide posing a cancer risk for humans has been strengthened,"[19] and that "compared with many regulated food carcinogens, the exposure to acrylamide poses a higher estimated risk to European consumers."[17] HEATOX sought also to provide consumers with advice on how to lower their intake of acrylamide, specifically pointing out that home-cooked food tends to contribute far less to overall acrylamide levels than food that was industrially prepared, and that avoiding overcooking is one of the best ways to minimize exposure at home.[17]
Baking, grilling or broiling food significant concentrations of acrylamide. This discovery in 2002 led to international health concerns. Subsequent research has however found that it is not likely that the acrylamides in burnt or well-cooked food cause cancer in humans; Cancer Research UK categorizes the idea that burnt food causes cancer as a "myth".[14]
The World Health Organization (WHO) has set up a clearinghouse for information about acrylamide that includes a database of researchers and 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.[22]
Laboratory research has found that some phytochemicals may have the potential to be developed into drugs which could alleviate the toxicity of acrylamide.[23]
Mechanism of action
Glycidamide is the dangerous metabolite produced from acrylamide, which in turn is produced by heating certain proteins.
Acrylamide is metabolized to the genotoxic derivative glycidamide. On the other hand, acrylamide and glycidamide can be detoxified via conjugation with glutathione.[24][25]
Occurrence in food
Hot french fries are heated to a high temperature.
Acrylamide was discovered in foods, mainly in starchy foods, such as potato chips (UK: potato crisps), French fries (UK: chips), and bread that had been heated higher than 120 °C (248 °F). Production of acrylamide in the heating process was shown to be temperature-dependent. It was not found in food that had been boiled,[26] or in foods that were not heated.[27]
Acrylamide has been found in roasted barley tea, called mugicha in Japanese. The barley is roasted so it is dark brown prior to being steeped in hot water. The roasting process produced 200–600 micrograms/kg of acrylamide in mugicha.[28] This is less than the >1000 micrograms/kg found in potato crisps and other fried whole potato snack foods cited in the same study and it is unclear how much of this is ingested after the drink is prepared. Rice cracker and sweet potato levels were lower than in potatoes. Potatoes cooked whole were found to have significantly lower acrylamide levels than the others, suggesting a link between food preparation method and acrylamide levels.
Acrylamide levels appear to rise as food is heated for longer periods of time. Although researchers are still unsure of the precise mechanisms by which acrylamide forms in foods,[29] 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).[30][31]
The US FDA has analyzed a variety of U.S. food products for levels of acrylamide since 2002.[37]
Occurrence in cigarettes
Cigarette smoking is a major acrylamide source.[38][39] It has been shown in one study to cause an increase in blood acrylamide levels three-fold greater than any dietary factor.[40]
See also
Acrydite: research on this compound casts light on acrylamide
^Mendel Friedman (2003). "Chemistry, Biochemistry, and Safety of Acrylamide. A Review". J. Agric. Food Chem. 51 (16): 4504–4526. doi:10.1021/jf030204+. PMID14705871.
^Friedman, Mendel (2003). "Chemistry, Biochemistry, and Safety of Acrylamide. A Review". Journal of Agricultural and Food Chemistry. 51 (16): 4504–4526. doi:10.1021/jf030204+. PMID14705871.
^Tareke, Eden; Rydberg, Per; Karlsson, Patrik; Eriksson, Sune; Törnqvist, Margareta (August 2002). "Analysis of Acrylamide, a Carcinogen Formed in Heated Foodstuffs". Journal of Agricultural and Food Chemistry. 50 (17): 4998–5006. doi:10.1021/jf020302f. PMID12166997.
^Ono, H.; Chuda, Y.; Ohnishi-Kameyama, M.; Yada, H.; Ishizaka, M.; Kobayashi, H.; Yoshida, M. (March 2003). "Analysis of acrylamide by LC-MS/MS and GC-MS in processed Japanese foods". Food Additives and Contaminants. 20 (3): 215–220. doi:10.1080/0265203021000060887. PMID12623644. S2CID9380981.
^Jung, MY; Choi, DS; Ju, JW (2003). "A Novel Technique for Limitation of Acrylamide Formation in Fried and Baked Corn Chips and in French Fries". Journal of Food Science. 68 (4): 1287–1290. doi:10.1111/j.1365-2621.2003.tb09641.x.
^Mottram D.S.; Wedzicha B.L.; Dodson A.T. (2002). "Acrylamide is formed in the Maillard reaction". Nature. 419 (6906): 448–449. doi:10.1038/419448a. PMID12368844. S2CID4360610.
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