Problem description:
Why does the non-stick coating in the rice cooker fall off so easily? What is a non-stick coating, which is harmless to eat after peeling off?
Analysis:
From a health point of view: non-stick pan is not as healthy as iron pan.
With the decision of the US Environmental Protection Agency (EPA), eight chemical companies, including DuPont, were ordered to gradually reduce or even stop using ammonium perfluorooctanoate (PFOA), which is the core component needed to manufacture Teflon coatings. At this point, the "Teflon dispute" that lasted for three years finally set the official tone. Experts from the World Health Organization (WHO) suggest that people should choose safe and healthy porcelain.
According to the requirements of the Environmental Protection Agency, the use of PFOA will be reduced by 95% in 20 10, and it will be completely banned in 20 15.
The reason why the non-stick pan is not sticky is that there is a coating called Teflon at the bottom of the pan. This substance is the general name of fluororesin, including polytetrafluoroethylene, perfluoroethylene propylene and various fluoropolymers. Because these compounds have the advantages of high temperature resistance, low temperature, self-lubrication and good chemical stability, they are widely used in non-stick pans, waterproof and breathable materials (such as waterproof clothing), leather, automobile parts, popcorn bags in microwave ovens and so on.
PFOA is an essential additive in PTFE production. Although there is no trace in the finished product, it may still decompose at high temperature. It is found that PTFE releases more than a dozen harmful gases at high temperature, which leads to the death of some animals with sensitive respiratory tract. However, the toxic effects of these gases on human body have not yet been determined.
PFOA with stable chemical properties will exist for a long time after entering the natural environment and human body, and will not decompose quickly. Studies have shown that low-dose PFOA not only appears in rivers, oceans and soils, but also exists in human blood. Because this artificial compound has been proved to have carcinogenic effect and other adverse consequences in animal experiments, if it exists widely in the natural environment and human body, the consequences will be worrying.
Non-stick pan cannot be used to make acidic food unless the temperature is limited below 250℃. According to the survey, the non-stick pans currently on the market are not marked with this restrictive use condition.
The main raw material of non-stick pan coating is PTFE. 1 990 May1day, the Ministry of Health approved the implementation of the national mandatory standard "Hygienic standard for PTFE coating on the inner wall of food containers", which stipulated the hygienic requirements for PTFE coating on the inner wall of food containers. "This standard is applicable to PTFE coating with PTFE as the main raw material, adding certain additives, coating on metal surfaces such as aluminum and iron plate, and then sintering at high temperature as anti-sticking coating for non-acidic food containers.
For the purpose of the national standard, researcher Han of the Standards Department of the Health Supervision Center of the Ministry of Health, who is responsible for the interpretation of the standard, affirmed: "The standard has two restrictions on the use of non-stick pans. One is that the non-stick pan cannot be used as acidic food, and the other is that the use temperature should be limited below 250℃. The coating of non-stick pan is sintered by PTFE and other additives. This standard is formulated for testing coating quality. At the same time, the conditions it defines are also the limiting conditions when using non-stick pans. "
● Why can't a non-stick pan make acidic food?
Professor Guan Cong, a fluoride expert, deputy secretary-general of the nonmetallic materials professional committee of the Chinese Society of Corrosion and Protection, and director of the Institute of Chemical Engineering of Shandong University, said: "PTFE has a congenital defect, that is, the bonding strength is not high, the non-stick pan is not completely covered with PTFE coating, and some parts always touch the metal surface. Acidic substances are easy to corrode the metal body, and once the body is corroded, it will expand, thus expanding the coating and causing the coating to fall off in a large area. The relevant standards of the Ministry of Health are based on this principle. " Professor Guan also believes that "the coating is mainly used for anti-sticking, but it is sprayed with a thin layer, and the combination is not reliable. Cooking with a shovel is definitely not acceptable. "
● What is acidic food?
"Acidic food includes all kinds of meat, eggs, sugar, rice, etc." Professor Yu Kang, director of the Nutrition Department of Peking Union Medical College Hospital, explained that acidic food is acidic or alkaline, not by taste, but by scientific means to detect the types and quantities of elements contained in food. Many foods we eat every day are acidic foods.
● All non-stick pans can't be used as acidic food?
Wang Fuhui, director of the State Key Laboratory of Metal Corrosion and Protection, Institute of Metals, Chinese Academy of Sciences, said that it depends on the materials used in the pot. Non-stick pans sold in the market are mainly made of three materials: aluminum alloy with a thick layer of aluminum oxide on the surface; Stainless steel, with a layer of chromium oxide on the surface, has strong corrosion resistance and slow corrosion; There is also iron, which is easily corroded by acid in a large area, thus coating. Wang Fuhui emphasized: "It is impossible to make acidic food with a non-stick pan made of corrosive metals such as iron. Non-stick pan made of metal with strong corrosion resistance, try not to make acidic food. "