Acrylamide

Acrylamide is an organic compound of the amide type, whose CAS number is 79-06-1. It is white, odorless, and crystalline, soluble in water, ethanol, ether, and chloroform. It forms in foods during cooking or processing at high temperatures (especially starchy products), and is also a component of tobacco smoke. It polymerizes easily, and polyacrylamide has many applications in the chemical industry, for example as a flocculant to clarify drinking water, in "in situ" in dams and tunnels, as a binder in the paper industry, in cosmetics, gene synthesis in the laboratory, metal extraction, textile industry, obtaining dyes, etc.

Acrylamide is classified as probably carcinogenic to humans (IARC 2A) based on animal studies. As of 2019, epidemiological studies suggest that dietary acrylamide consumption is likely to increase people's risk of developing cancer.

Summary

The formation of acrylamide in food is mainly due to a variant of the Maillard reaction, which is also responsible for the typical flavor, color and aroma of fried or grilled products. In this specific case, the reaction occurs between glucose and the amino acid asparagine, which is decarboxylated and deaminated to form acrylamide.

Other formation mechanisms have also been identified, for example, pyrolysis of gluten (a wheat protein), and enzymatic decarboxylation of asparagine in raw potatoes. These routes are very minor, and the degree to which they contribute to the formation of acrylamide in food has not yet been investigated. Acrylamide forms at temperatures above 120°C. The quantity produced depends on the recipe, the processing time and temperature. We can find it in a wide variety of foods, industrially prepared, in restaurants or at home. The products that contain the most acrylamide are potato chips, French fries, toast, cookies and pastries.

Metabolism

Rodents and humans metabolize acrylamide to a reactive epoxide (glycidamide), in a reaction catalyzed by cytochrome P450 (CYP2E1). In humans there are differences in metabolism due to interindividual variability in the amount of the CYP2E1 enzyme.

Glycidamide can be metabolized by epoxide hydrolase to glyceramide, can also be conjugated with glutathione, react with proteins (hemoglobin), or with DNA.

Acrylamide can form adducts with hemoglobin, and can also conjugate with glutathione to form mercaptopuric acid (N-acetyl-S-(2-carbamoylethyl)-L-cysteine) which is subsequently oxidized to its corresponding sulfoxide.

Risks

Toxic effects from a single oral dose only occur with doses greater than 100 mg/kg, and the lethal dose 50 (LD50) is, as a general rule, above 150 mg/kg.

Several studies in different animal species show that the main damaged organ is the nervous system. Repeated exposure to acrylamide causes degeneration in areas of the brain (cerebral cortex, cerebral thalamus, and hippocampus) critical for memory, learning, and other cognitive functions, and also affects peripheral nerves. In rodent reproduction studies, males show reduced fertility, affecting sperm count and sperm morphology.

In humans, epidemiological studies suggest that the nervous system is also the site of action of acrylamide. The relationship between occupational or dietary exposure with the development of cancer has not yet been conclusively demonstrated. Although some studies indicate an association with some types of tumors, particularly hormone-related in women and pancreatic cancer.

It is estimated that there is a mean exposure through the diet of between 0.2 and 1.0 μg/kg/day in the adult population. In heavy consumers it is assumed that it can be from 1.0 μg/kg/day to 4 μg/kg/day.

The World Health Organization considers acrylamide to belong to the group of chemicals that do not have an identifiable threshold above which they show effects. This means that a low concentration carries a low risk, but there is always a risk if the poison is ingested. An important requirement for making decisions requires knowing the nature and level of risk, as well as the possibility of reducing it. The problem is that this type of information is not currently available regarding acrylamide.

Prevention and control

The reduction and control of acrylamide in food has been carried out voluntarily by the food industry. The authorities also provide information to consumers on how to reduce the formation of acrylamide in homemade foods. The Codex Alimentarius Commission has recently adopted the Code of Practice for Reducing Acrylamide in Foods.

Although more and more control methods are being published, there is still no single method that can efficiently reduce acrylamide levels in all foods. Some measures that have been taken at the level of the food industry have been to control sugar levels in potatoes, treatment with the enzyme asparaginase, addition of salts and acids, temperature control during cooking, and control of humidity and browning in the final product.

Acrylamide is found mainly in the brownest part of food, such as French fries or the edge of cookies. Recently, it has been found that acrylamide is also produced in the coffee roasting process. On a domestic scale, the way to reduce the acrylamide content in food is by using lower frying temperatures. An option that the EU also recommends for the industry is washing in cold water for a few minutes or blanching with boiling water after chopping the potatoes and before frying them.