In the city, there is such a group of people, they salvage the waste cooking grease in the sewers - "gutter oil" to make huge profits. As the low temperature makes the grease in the sewer condense into a white, gray or brown solid, "obediently" stay in the sewer, which gives them more convenient work. A large part of the fished out "gutter oil" is refined and sold again to return to people's tables. China Agricultural University Food Science and Nutritional Engineering, vice president of Hu Xiaosong in a CCTV program, said publicly that every year there are millions of tons of "gutter oil" into the market, on the table, which is mainly in the rural market and urban and rural markets, canteens, collective canteens. "Gutter oil" 20 years of history "you must have eaten gutter oil. I often joke that I eat 'gutter oil' for breakfast every morning. In terms of quantity, I think it's possible that 1.5 million tons of 'gutter oil' enter the market a year; it's not as scary as melamine, but its harm is always there." He Dongping, a professor at the School of Food Science and Engineering at Wuhan Institute of Technology, who has long been engaged in research on oil and grease, told Science News. "Gutter oil" is also known as "gross oil" by industry insiders, and its sources mainly include: greasy floaters in the sewers; leftovers from hotels and restaurants that have been simply processed and refined; oil used for deep-frying food that has been used more than the specified number of times, or poor-quality pork and pork lard. Or poor-quality pork, pig offal, pig skin processing and refining the output of the oil. The recovered "gutter oil" usually flows into the food and catering industry after being blended with some new oil. According to experiments, long-term intake of "gutter oil" will cause harm to the human body, such as developmental disorders, susceptibility to enteritis, and liver, heart and kidney enlargement, as well as fatty liver and other lesions. In addition, "gutter oil" contaminated with aflatoxin is not only easy to make people develop liver cancer, but also may lead to other parts of the cancer, such as gastric adenocarcinoma, kidney cancer, rectal cancer and breast cancer, ovary, small intestine and other parts of the cancer. "Although we know that there are such unspoken rules in the food industry, and we know that there are unscrupulous businessmen selling substandard oils for profiteering, it is difficult for us to tell the difference." Hu Xiaosong has said, "Oil adulterated with oil, the gods are worried, the gods are hard to separate it, so 'gutter oil' should probably have been around for more than 20 years. If calculated by tonnage, the annual digestion of 'gutter oil', collectively, it should be in the millions of tons." It is understood that the refining of a ton of catering industry "gutter oil" costs only about 300 yuan, and if it is processed into biodiesel costs about 1,000 yuan per ton. In the eyes of experts, the profit motive is "gutter oil" long-term rampant one of the important reasons. However, for the scientific research community, also has its own responsibility, because this should be for the "gutter oil" to act as a gatekeeper of the detection method is still lacking, can not be completely "disguised" after the "gutter oil "pulled out, which makes" gutter oil "in the market can be unimpeded. Difficulty of detection After refining the "gutter oil", from the appearance and sensory difficult to distinguish from ordinary oil. China Agricultural University Food Science and Nutritional Engineering Associate Professor Shen Qun said that at present there are a number of gutter oil detection methods, but there is a detection method can not be used to detect all the sources of "gutter oil" defects (different sources of "gutter oil" characteristics are different). Sometimes the detection error is large and there is a possibility of misjudgment. If the amount of "gutter oil" adulterated is small, it cannot be detected. The existing patents on "gutter oil" detection that Science News has learned about include the conductivity detection method and the cholesterol detection method. Among them, the conductivity detection method is based on the fact that fats and oils are exposed to a large amount of salt, monosodium glutamate (MSG), detergents, etc., during the cooking process, the metal ion content is higher than that of ordinary first-grade oils, and there is a clear correlation between the amount of "gutter oil" added to the oils. The idea behind the cholesterol test is that used oils, due to their mixing with animal fats in the earlier cooking process, contain no or very little cholesterol in vegetable fats and oils, while animal fats have higher cholesterol content. Liu Zhijin, a student at Wuhan Institute of Technology, invented a method to accurately detect "gutter oil" in 30 minutes. The principle lies in: "gutter oil" from the sewer washing oil water, which contains a lot of metal ions from the gutter, metal utensils, detergents, compared with normal food oil has a difference. Therefore, they use the metal ion concentration and conductivity of the relationship between the conductivity of the oil through the detection of the conductivity of the "gutter oil" conductivity is the first level of cooking oil 5 to 7 times, and thus determine the "gutter oil". In May of the same year, Wang Le, also a master's degree student at the Wuhan Institute of Technology, developed a blue test paper, by placing the test paper into the tested oil and then take it out and leave it for half a minute to observe the color change and compare it with the standard color card to determine whether or not it is adulterated with "gutter oil". Wang Le has introduced to the media, the experimental results show that the test paper judgment correct rate of up to 90% or more. However, she also made it clear that due to the excessive impurities and complex cost of oil after cooking, the test paper, which is the result of her own research, could not directly test the oil used in cooked dishes. Wang Le's research results, Wuhan Institute of Technology Professor He Dongping analysis, which is based on the oil's "cumulative nature" to detect the purity of the oil, when there is sodium chloride in the oil, the cumulative nature of large, and vice versa is small. The regular channels of cooking oil usually do not have sodium chloride. Huang Fenghong, a researcher at the Oilseed Crops Research Institute of the Chinese Academy of Agricultural Sciences, pointed out that the two methods mentioned above have shortcomings, saying, "The lower limit of detection for the conductivity method is more than 20% of the amount of 'gutter oil' added, and the flaw of the cholesterol method is that its lower limit of detection is 'gutter oil' addition is above 10 percent." Science News contacted a company that produces "'gutter oil' rapid test kits." The kit designed by the company uses thin-layer chromatography to detect "gutter oil". But the reporter saw in the manual, which is clearly marked, "for some unpurified oil (such as sesame oil, pepper oil, etc.) and add other components of the oil (such as chili oil), this method is prone to false positives." In the course of the reporter's consultation, the sales staff also said that the kit can only be used as industrial and commercial law enforcement, can not be analyzed in detail. R & D new tricks According to reports, after refining "gutter oil" although after a series of processes, including cooking, separation, collection, refining, etc., but after washing, distillation, decolorization, deodorization and other processing processes, affecting the sensory and appearance of the factors are ruled out, and its main component is still triglyceride, which is no different from ordinary fats and oils, itself The main component is still triglyceride, which is no different from common fats and oils, and it does not show the unique characteristics that are significantly different from other fats and oils, so there is no sufficient basis for the establishment of effective and efficient detection methods. For the detection of "gutter oil", He Dongping also said that a single method cannot be used. "The detection of 'gutter oil' must be judged comprehensively." He said. In the face of all the difficulties of gutter oil detection, the Ministry of Science and Technology last year specifically for this project. The project is undertaken by Huang Fenghong, a researcher at the Oilseed Crops Research Institute of the Chinese Academy of Agricultural Sciences, and his team. In response to the characteristics of "gutter oil" and the limitations of some existing methods, Huang and his colleagues adopted a new approach. He told Science News that, in response to the characteristics of "gutter oil" itself, they have adopted a simultaneous approach from several aspects, including the detection of polar compounds and polymers, the detection of Steradienes (β-sitosterol oxidized at high temperature), the detection of trans fatty acids, the detection of heavy metals and biotoxins, and the detection of the content of heavy metals and biotoxins, in addition to the two methods mentioned above. Detection of heavy metals and biotoxins, and the use of electronic nose technology to establish the fingerprints of different oils and fats, based on the establishment of the above methods, to explore the correlation between several parameters, so as to determine the existence of "gutter oil". The harm of gutter oil to human body: Anal experts explain, "gutter oil" is really the enemy of people's health, especially for people's gastrointestinal health, has an immeasurable destructive power. 1, "gutter oil" will lead to indigestion: in the process of refining "gutter oil", animal and vegetable oils after contamination by rancidity, oxidation and decomposition of a series of chemical changes, resulting in heavy toxicity to the human body; arsenic, which is one of them, once a person Once a person uses "gutter oil" with a huge amount of arsenic, it will cause indigestion, headache, dizziness, insomnia, fatigue, liver discomfort and other symptoms. 2, "gutter oil" will lead to diarrhea: "gutter oil" production process is destined to be unhygienic, which contains a large number of bacteria, fungi and other harmful microorganisms once they reach the human intestinal tract, the lesser will trigger diarrhea, the more serious will cause nausea, vomiting and a series of gastrointestinal diseases. A series of gastrointestinal diseases. 3, "gutter oil" will cause intense abdominal pain "gutter oil" mixed with a lot of sewage, garbage and detergent, after the open-air refining of underground workshops, it is impossible to remove bacteria and harmful chemical components. It is an indisputable fact that all "gutter oil" contains lead in excess of the standard, and consumption of food made of "gutter oil" containing excessive lead will cause severe abdominal cramps, anemia, toxic liver disease and other symptoms. 4, "gutter oil" can lead to stomach cancer, intestinal cancer: sickening refining process, is gutter oil toxin breeding reasons. "Gutter oil" is from hotels, restaurants to receive driving rain (slop, leftovers, etc.) and gutter oil processing and refining to remove the odor and flow to the cooking oil market finished oil. Driving oil contains aflatoxin, benzo(a)pyrene, these two toxins are carcinogenic substances, can lead to stomach cancer, intestinal cancer, kidney cancer and breast, ovary, small intestine and other parts of the cancer. Anal experts remind consumers that once abdominal pain, nausea, vomiting and other symptoms occur after eating at restaurants, food stalls or vendors, you must go to the hospital for treatment in the first time to avoid causing more harm to your body. Junk oil is non-edible oil that is of extremely poor quality and unhygienic, with peroxide value, acid value, and moisture seriously exceeding the standard. It contains toxins, which will cause nutrientization of water bodies if it flows into rivers. Once consumed, it will destroy white blood cells and the mucous membranes of the digestive tract, cause food poisoning, and even cause cancer. One of the "vegetable oils" is frying oil, which is used repeatedly for a long time at high temperature, and in contact with oxygen in the air, hydrolysis, oxidation, polymerization and other complex reactions occur, resulting in an increase in the viscosity of the oil, deepening of the color, peroxide value, and the production of volatiles and aldehydes, ketones, lactones and other irritating odor substances, which have carcinogenic effects. "Swill oil" in the main hazards ----- aflatoxin toxicity is arsenic 100 times.