High-temperature cooking methods like baking, frying, and grilling create the appealing taste and texture of foods but may produce harmful compounds like acrylamide. Discovered in 2002, acrylamide forms when reducing sugars react with asparagine during high-temperature cooking (above 120°C), especially in starchy foods like chips, fries, and baked goods.
Baking, grilling and frying, these cooking methods can bring special flavor and color to food, but they also bring some harm.
The brown color, tempting aroma, and rich taste, foods with these characteristics often make people feel the beauty of life. However, most of these foods are baked, grilled and fried foods, which are not only high in fat content, but may also cause a series of health problems.
As early as 20 years ago, there was a global discussion about the potential harm of these foods to health. In April 2002, the Swiss Food Administration (SNFA) and scientists from Stockholm University issued a warning about food safety at a press conference. This means that some high-starch foods will produce very high levels of acrylamide (AA) after high-temperature cooking (baking, grilling or frying, cooking temperature exceeds 120°C), which is about 500 times the acrylamide content in drinking water stipulated by the World Health Organization (WHO).
The press conference warned people to pay attention to the fact that the content of acrylamide in food is much higher than other known food carcinogens, including polycyclic aromatic hydrocarbons and ethyl carbamate.
Reducing sugar + amino acid = toxic?
The news of SNFA had a short-lived and strong impact in Switzerland. Within three days of the news, the sales of potato chips in Switzerland dropped by 30%-50%, and the stock prices of several local fried food companies also fell rapidly. However, a few days later, the sales of potato chips began to pick up. Some Swiss scientists and media also began to speak out, saying that the warning of SNFA was a bit exaggerated. However, the harm of acrylamide has begun to be taken seriously by many international organizations and scientists.
Just two months later, WHO and the Food and Agriculture Organization of the United Nations (FAO) jointly released a 23-page report, which detailed the formation process of acrylamide and its potential health hazards. In this report, they pointed out that the ingestion of acrylamide through food is a major cause of people's exposure to acrylamide.
Acrylamide is not a component of the food itself, but comes from a non-enzymatic browning reaction in the cooking process of food - the Maillard reaction. This reaction can be summarized as when food is cooked at a high temperature of more than 120°C, some reducing sugars and amino acids in it will undergo a series of polymerization reactions and eventually form brown melanoidins. This process will form many unique flavor substances, giving grilled and fried foods a unique taste and color. The "stir-fried sugar color" when cooking is actually a caramelization reaction (a non-enzymatic browning reaction). At a high temperature of about 160°C, sugar substances will dehydrate and polymerize, etc. As the high temperature time increases, the color gradually deepens, and finally changes from caramel color to dark brown.
Acrylamide is formed by reducing sugars (including glucose, fructose, etc.) and an amino acid called asparagine through the Maillard reaction. Many foods contain reducing sugars and asparagine. It is conceivable that after high temperatures, these foods will contain a certain degree of acrylamide.
The WHO survey shows that among foods, potato chips have the highest acrylamide content. As the frying time of potato chips and French fries increases, the content of acrylamide will also rise sharply, and it is expected to increase by 10 to 20 times. In addition to potato chips, meat, milk, rice, biscuits, cassava and soy products will also contain a certain level of acrylamide. In addition, baked foods such as bread and coffee will also contain this compound. In addition to food sources, active or passive inhalation of cigarettes is also an important source of acrylamide intake.
Consequences of ingestion
In the past decade, scientists have fully understood the metabolic process of acrylamide in the body. According to the WHO report, the average daily intake of acrylamide per person is 0.3~0.8 micrograms/kg body weight, and the intake of children is 2~3 times that of adults. In addition, some consumers with special eating habits may have acrylamide intake several times the average level.
After these acrylamides enter the human body, they will be rapidly absorbed and distributed to many organs and tissues. In the tissues, they will be catalyzed by cytochrome P4502E1 (an enzyme) to form glycidamide (GA). Both acrylamide and GA can bind to hemoglobin, proteins, DNA and various enzymes in the human body.
After acrylamide enters the human body, it is catalyzed by enzymes to become glycidamide. Image source: Wikipedia
However, there is a barrier in our body - glutathione (which has antioxidant, integrated detoxification effects in the human body) to prevent the toxic effects of these compounds. Glutathione will bind most of the acrylamide and GA, so that these two compounds can be excreted through urine and no longer continue to harm the human body. GA can also be cleaved by epoxide hydrolase (EPHX1) in the body and excreted through urine. The remaining part that is not excreted may cause damage.
Current studies on rodents show that acrylamide and GA can cause neurotoxicity, reproductive toxicity, genotoxicity and carcinogenicity. Some scientists have found that both acrylamide and GA can be passed to the fetus through the mother's placenta, causing harm to the fetus. GA is more carcinogenic than acrylamide. It is more likely to combine with guanine and adenine on the genetic material DNA, causing mutations in these two bases, and then causing carcinogenic effects. According to a 2011 meta-study, the current daily intake of acrylamide by people does not reach a dose that has a carcinogenic effect, and it cannot lead to an increased risk of multiple cancers, but it will lead to an increased risk of kidney cancer-this may be the result of years of accumulation.
In terms of reproductive toxicity, some studies based on rodents have found that GA is an important cause of reduced reproductive capacity, sperm mutations and death in mice. One point worth noting is that the results of these mouse studies show that feeding large doses of acrylamide - more than 7 mg/kg body weight per day - will significantly harm reproductive capacity. This is about 10,000 times the amount of acrylamide humans consume from food every day. Obviously, in daily life, we are almost impossible to be exposed to so much acrylamide.
We need to be more vigilant about the neurotoxicity that acrylamide may cause, which only requires 1/10 of the exposure dose to produce reproductive toxicity. Neurotoxicity is prone to occur when acrylamide is accidentally ingested or exposed to an environment of acrylamide for a long time. In this case, the peripheral nerves and nerve endings of the human body will be lesioned, followed by cognitive dysfunction and damage to the cerebral cortex, thalamus and hippocampus.
Reduce the formation of acrylamide
Researchers from the Dutch Food Administration followed more than 60,000 middle-aged and elderly women for 11.3 years and found that the amount of acrylamide in the diet was positively correlated with the risk of endometrial and ovarian cancer in women. The most obvious difference between these people and others in their diet is that they like to eat onbijtkoek, a popular "breakfast cake" in the Netherlands. In addition, their preference for coffee, French fries, potato chips and cookies is also the reason for their higher acrylamide intake.
Researchers found that more reducing sugars - glucose and fructose - are added to onbijtkoek cakes during the production process, and baking soda (sodium bicarbonate, which can make the cake lighter and fluffier) is used. During baking, the weakly alkaline sodium bicarbonate creates an alkaline environment, which makes it easier for the amino groups in amino acids to lose protons and increase the reactivity with reducing sugars. This makes the Maillard reaction more likely to occur and acrylamide more likely to form.
Official agencies in many countries have ensured food safety by limiting the level of acrylamide in some sold foods. In daily life, we can also reduce acrylamide intake by changing some cooking methods. For example, when making French fries, soak the cut potatoes in hot water for 10 minutes to reduce the content of reducing sugars to reduce the formation of acrylamide - this can even reduce the amount of acrylamide produced by about 90%. We can also reduce the formation of acrylamide by lowering the cooking temperature of food. In addition, when baking, we can add asparaginase in advance to remove asparagine. Some scientists are also trying some more high-tech methods, such as using CRISPR gene editing technology to remove asparagine from wheat.
Future expectations
The problem of acrylamide reminds us that while pursuing deliciousness, we must also pay attention to health risks. With the advancement of science and technology, the improvement of food processing methods may significantly reduce the formation of this compound. For ordinary consumers, rationally adjusting eating habits and reducing the intake of high-temperature cooked foods are currently the most direct and effective ways to deal with it.
Maybe one day, the barbecue and French fries we eat will no longer contain acrylamide. But by then, will those mouth-watering colors, aromas and flavors remain the same? The balance between "health" and "delicious" may require us to redefine it in our choices.
Reference links:
https://apps.who.int/iris/handle/10665/39596
https://www.bbc.com/future/article/20230224-should-you-avoid-eating-burnt-food
https://aacrjournals.org/cebp/article/16/11/2304/277087/A-Prospective-Study-of-Dietary-Acrylamide-Intake
https://www.sciencedirect.com/topics/chemistry/ dominant-lethal https://apps.who.int/iris/bitstream/handle/10665/42563/9241562188.pdf?sequence=1 https://pubmed.ncbi.nlm.nih.gov/14530144/ https://www.annalsofoncology.org/article/S0923-7534(19)38426-1/fulltext https://www.annalsofoncology.org/article/S0923-7534(19)38426-1/fulltext