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Photo: Pixabay baking, barbecue and frying, these cooking methods can bring special flavor and color to the food, but also bring some harm.

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Scorched yellow color, attractive oil flowers and fragrance, coupled with the rich taste of activating taste buds, foods with these characteristics often make us feel the beauty of life. But here, I may remind you of some briefly forgotten facts: most of these foods are baked, barbecued and fried, which are not only high in fat, but can also lead to inflammation.

There was a global discussion as early as 20 years ago about the potential health hazards of these foods. In April 2002, scientists from the Swiss Food Administration (SNFA) and Stockholm University issued a warning about food safety at a news conference. Generally speaking, some high-starch foods are cooked at high temperatures (baked, barbecued or fried at temperatures above 120 ℃) to produce high levels of acrylamide (acrylamide,AA), which is about 500 times the level of acrylamide in drinking water prescribed by the World Health Organization (WHO).

This warning follows a number of studies that have confirmed the neurotoxicity of acrylamide and are associated with the risk of some cancers. However, another alarming point at the news conference is that the level 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 SNFA news produced a brief and powerful shock in Switzerland. Within three days of the news, potato chip sales in Switzerland fell by 30% and 50%, and the share prices of several local fried food companies also fell rapidly. But a few days later, sales of potato chips began to pick up. Some scientists and media in Switzerland have also begun to speak out, saying that SNFA's warning is a bit exaggerated. However, although the impact of acrylamide on the public at that time gradually dissipated, its harm began to attract the attention of many international organizations and scientists.

Photo: just two months after Pixabay, WHO and the Food and Agriculture Organization of the United Nations (FAO) released a 23-page report detailing the formation of acrylamide and its potential health hazards. In this report, they point out that ingestion of acrylamide through food is a major reason for people's exposure to acrylamide.

Acrylamide is not an ingredient of food itself, but comes from a non-enzymatic browning reaction during food cooking-Maillard reaction (Maillard reaction). This reaction can be summed up as when food is cooked at a temperature of more than 120 ℃, some of the reducing sugars and amino acids go through a series of polymerization processes to form brown melanin-like substances. This process will form many unique flavor substances, giving barbecue and fried food a unique taste and color. The "fried sugar color" when cooking is actually caramelization (a non-enzymatic browning reaction). At a high temperature of about 160℃, sugars will dehydrate and polymerize. With the extension of the high temperature, the color gradually deepens, from caramel color to dark brown.

Acrylamide is formed from reducing sugars (including glucose, fructose, etc.) and an amino acid, asparagine, by Maillard reaction. Many foods contain reducing sugar and asparagine, it is conceivable that after high temperature, these foods will contain a certain degree of acrylamide.

WHO's survey shows that potato chips have the highest acrylamide content in food. With the extension of the frying time of potato chips and French fries, the content of acrylamide will also increase sharply, which is expected to increase by 10 to 20 times. In addition to potato chips, meat, milk, rice, biscuits, cassava and bean products also contain certain levels of acrylamide. In addition, this compound can also be found in baked goods such as bread and coffee. In addition to food sources, active or passive inhalation of cigarettes is also an important source of acrylamide intake.

The consequences of ingesting the body for nearly a decade, scientists have fully understood the metabolic process of acrylamide in the body. According to the WHO, the average daily acrylamide intake per person is 0.3 to 0.8 micrograms per kilogram of body weight, while children's intake is 2 to 3 times that of adults. In addition, some consumers with special eating habits may have acrylamide intake several times the average.

When these acrylamides enter the human body, they are quickly absorbed and distributed in many organs and tissues. In tissue, they are catalyzed by cytochrome P4502E1, an enzyme, to form glycidyl amide (glycidamide,GA). Both acrylamide and GA can bind hemoglobin, protein, DNA and various enzymes in the human body.

After entering the human body, acrylamide is transformed into glycidyl amide by enzyme catalysis. Photo Source: Wikipedia, however, there is a barrier in our bodies-glutathione (which has the effect of antioxidation and integrated detoxification in the human body) can prevent the toxic effects of these compounds. Glutathione binds most of acrylamide and GA so that these two compounds can be excreted through the urine and no longer harm the body. GA can also be cleaved by epoxide hydrolase (EPHX1) and excreted through urine. And the rest of the undischarged part is likely to cause damage.

Current studies on rodents have shown that both acrylamide and GA can cause neurotoxicity, reproductive toxicity, genotoxicity and carcinogenicity. Some scientists have found that both acrylamide and GA can be transmitted to the fetus through the mother's placenta, causing harm to the fetus. The carcinogenicity of GA is higher than that of acrylamide, and it is more likely to bind to guanine and adenine on the genetic material DNA, resulting in these two base mutations, leading to carcinogenesis. According to a 2011 meta-extraction study, people's daily acrylamide intake does not reach a carcinogenic dose that does not increase the risk of multiple cancers, but can lead to an increased risk of kidney cancer-a result that may accumulate over the years.

In terms of reproductive toxicity, some studies based on rodents have found that GA is an important cause of decreased reproductive ability, sperm mutation and death in mice. Notably, these mouse studies showed that feeding large doses of acrylamide-more than 7 milligrams per kilogram of body weight a day-significantly harmed fertility. This is about 10, 000 times the daily intake of acrylamide from food. It is obvious that in ordinary life, it is almost impossible for us to be exposed to so much acrylamide.

Image source: pixabay what we need to be more vigilant about is the possible neurotoxicity of acrylamide. The exposure dose for this condition requires only 1 × 10 of reproductive toxicity. Neurotoxicity can easily occur when accidental intake of acrylamide or long-term exposure to acrylamide. In this case, pathological changes occur in the peripheral nerves and nerve endings, followed by cognitive impairment, as well as damage to the cerebral cortex, thalamus and hippocampus.

Reducing the formation of acrylamide can sometimes be difficult to prevent because of imperceptible but long-standing eating habits. Researchers at the Dutch Food Administration found a similar situation in a questionnaire study. They followed more than 60,000 middle-aged and elderly women for 11.3 years and found that dietary acrylamide levels were positively correlated with women's risk of endometrial and ovarian cancer. The most obvious difference between these people and others in their diet is that they like to eat onbijtkoek, a popular Dutch "breakfast cake". In addition, their preference for coffee, French fries, potato chips and biscuits was also the reason for their higher acrylamide intake.

Image source: Pixabay researchers found that onbijtkoek cakes add more reducing sugar-glucose and fructose-and use baking soda (sodium bicarbonate, which makes the cake lighter and fluffy). During baking, weakly alkaline sodium bicarbonate creates an alkaline environment that makes the amino groups in amino acids more likely to lose protons and react more actively with reducing sugars. This will cause Maillard reaction to occur more easily and acrylamide to form more easily.

Official agencies in many countries have ensured food safety by limiting the level of acrylamide in some foods on sale. At present, China is mainly based on the benchmark level set by the European Union (750 μ g / kg) to detect acrylamide in food, but many potato chip products will exceed this benchmark. An ongoing survey conducted by the US Food and Drug Administration (FDA) shows that acrylamide levels in potato chips and biscuits are decreasing, but there is no significant change in other foods.

In fact, there has always been a difficulty in the study of acrylamide, that is, it is impossible to determine how much acrylamide each of us consumes, and there are no urine and blood biomarkers for reference. These limit the detailed study of the toxicological effects of acrylamide in humans. For example, current studies have confirmed that acrylamide increases the risk of endometrial and ovarian cancer in women, but no exact cause has been found. Some theories suggest that acrylamide may have an effect on hormones in women.

Even so, in daily life, we can actually change some cooking methods to reduce acrylamide intake. For example, when making French fries, soaking cut potatoes in hot water for 10 minutes reduces the formation of acrylamide by reducing the content of reducing sugar-which can even reduce the production of acrylamide 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 more high-tech methods, such as using CRISPR gene editing to remove asparagine from wheat. Maybe one day, acrylamide will disappear from barbecue, baked and fried foods, and then will we feel the taste of these foods change and lack some feeling?

Reference link:

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

This article comes from the official account of Wechat: global Science (ID:huanqiukexue)

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