I don’t mean to spoil your appetite, but dear friends, when you take the first subway to work in the morning with a few fried dough sticks; When you are standing on the street munching on mutton kebabs; Do you realize that you are in danger when you order a pot of delicious boiled fish for your child?
Danger comes from oil. I don’t know since when, urban sewers have become places where some people get rich. Every day, they get a lot of dim, turbid and slightly red paste from there. After only one night of filtration, heating, precipitation and separation, they can make this.Some stinking garbage turned into clear "edible oil" and finally returned to people’s tables through low-priced sales. This three-no product, called "waste oil", is still composed of triglycerides, but there are many more toxic substances that cause disease and cancer than real edible oil.
"You must have eaten gutter oil, too." He Dongping, a professor at the School of Food Science and Engineering of Wuhan Institute of Technology, told the China Youth Daily reporter. His other identity is the head of the oil and grease working group of the National Grain and Oil Standardization Committee. According to his estimation, at present, there are 2 million to 3 million tons of waste oil returning to the table every year in China. The total consumption of animal and vegetable oil in Chinese is about 22.5 million tons a year-that is to say, according to the proportion, if you eat 10 meals, one meal may come across gutter oil.
In an era of paying attention to food safety, the ideal state is that when you go to a restaurant, you take out a test paper and dip it in the dish. After a while, you take it out and compare it with the spectrum table, and then shout, "Boss, change the oil!" But the reality is that up to now, scientists have not found an ideal means to detect and identify gutter oil.
A Scientific Investigation on the Influence of Appetite
At the beginning of the new semester, nine senior students from the School of Food Science and Engineering of Wuhan Institute of Technology received their new task-investigating the situation of waste oil in three towns of Wuhan.
"This is a survey that affects appetite." Jiang Shan, head of the investigation team, said that sampling is their core task. So, this group of college students put on old clothes and gloves, and lie on the side of the sewer near the restaurant every day. Fortunately, it is winter, low temperature condenses oil into semi-solid, and sewers are not as smelly as summer. The students used shovels to dig out the "red and white" floating objects and put them in plastic bags. However, you have to be careful in doing these things, because the instructors have repeatedly reminded you, "Be careful of those who recycle waste oil, they will beat people."
Compared with the "sneaking around" of college students, the professional recyclers of gutter oil are really "aboveboard". All they need is a shovel, a few worn-out iron drums and an electric car, and they can go home with a full load, at most, they can bring an extra flashlight when it is dark.
Sometimes when we meet in a narrow road, the students’ actions of digging oil will inevitably attract some hostile eyes, and some people have come to ask "why". The students were so nervous that they faltered that they wanted to "take it back to feed the dog".
During the investigation, the students learned that the cost of extracting 1 ton of gutter oil from the kitchen waste in the catering industry is only about RMB in 300 yuan. In their view, profit-driven is one of the main reasons for the long-term existence of waste oil. People who dig gutter oil seem inconspicuous. In fact, they can earn 70 to 80 yuan on average by digging a barrel of oil. A person can usually pay 4 barrels a day. After recycling and refining, even if it is sold at half the market price of edible oil, it can earn more than 10,000 yuan a month, which is equivalent to the income of senior white-collar workers. Someone told the students that in this line, even odd jobs earn 2,500 yuan a month.
Because of paying attention to the food culture of frying, frying and stewing, extravagance and waste, a large amount of kitchen waste and gutter oil derived from it have become a unique phenomenon in China. In the survey, the students found that in Wuhan, even the stalls selling fish soup paste powder produce about 15 kilograms of kitchen waste every day. It is estimated that there are more than 60,000 restaurants in Wuhan, which produce about 252,000 tons of kitchen waste and 126,000 tons of waste oil every year.
Therefore, in such a city, digging gutter oil has become a profiteering industry. Some people monopolize the kitchen waste in some restaurants and send someone to buy it every day. A city is usually divided into several spheres of influence.
It is in such a harsh "competitive environment" that the students of the investigation team obtained more than 60 samples by "stealing openly and stealing secretly". These samples of waste oil in glass bottles are now stored in the freezer of the laboratory with labels such as "Sichuan restaurant" and "boiled fish". Although the bottle cap is tightly plugged, there are still some pungent and sour smells from time to time. It is said that this is "aldehyde produced after rancidity of unsaturated fatty acids".
After completing the sampling work, the students of the investigation team inspected the catering market in Wuhan by the way, and found that some breakfast stalls were impressively equipped with two pots, one with a good oil label and the other without a label, which was "obviously turbid". There is also a takeaway mutton kebab in the university town, always taking a Sprite bottled oil, and those "golden oil" are full of sediment.
"Wuhan is just a microcosm." Jiangshan said that in hundreds of cities in China, waste oil is recycled wherever there is a catering industry. Conversely, because of the low price, these waste oils eventually returned to the catering industry, from street shops to five-star hotels.
The results of medical research show that long-term intake of waste oil will cause obvious harm to human body, such as developmental disorder, enteritis, hepatomegaly, heart and kidney enlargement and fatty liver. Aflatoxin, one of the main hazards in gutter oil, is a strong carcinogen, and its toxicity is 100 times that of arsenic.
Another problem is ethical. "The oil that others have eaten deteriorates in the sewer and is fished up again. Can people eat it?" A member of the investigation team frowned and said. During that time, there was always an "indelible smell" on his clothes. The investigation took only 10 days, but he lost his appetite for half a month.
Oil mixed with oil makes the gods worry.
Since the birth of the catering industry, gutter oil has inevitably appeared. However, when it was originally called "swill", it was usually only used to feed pigs, and it was only given to people in the last 20 years.
In the view of scientific researchers, the difficulty in treating gutter oil lies in that it is difficult to distinguish gutter oil from ordinary oil only from appearance and sense after refining processes such as washing, distillation, decoloration and deodorization. Illegal traders usually mix gutter oil into edible oil, and if the content is small, it is even more difficult to detect.
"People who engage in oil" all know a saying: "Oil mixed with oil makes the gods worry".
Professor He Dongping has been engaged in the research of gutter oil for 7 years. He and his research team are also undertaking the task of the National Standardization Administration Committee-"Research and formulation of the reuse standard of waste oil in urban kitchen waste". At present, the important task is to find an effective means to detect and identify gutter oil.
In He Dongping’s view, traditional detection methods only capture a certain characteristic of gutter oil, but none of them can effectively detect gutter oil from different sources at the same time, which sometimes leads to large detection error and more possibility of misjudgment. If the content of gutter oil is small, it can’t be detected.
Such as conductivity detection. Because the oil comes into contact with detergents and metal utensils during cooking, or stays in heavy metal environment for a long time, the conductivity value of gutter oil is obviously higher than that of ordinary edible oil. In Wuhan Institute of Technology, an undergraduate surnamed Liu once found a way to detect gutter oil within 30 minutes. By testing the conductivity of oil, he concluded that the conductivity of waste oil is 5~7 times that of first-class edible oil. This method is relatively effective for the detection of hogwash fat. However, its defect is that it is only suitable for the detection of food oil with more than 20% waste oil added.
The other is cholesterol test. Because gutter oil is a mixture of various animal and plant fats, among which animal fats generally contain cholesterol, while regular vegetable oils that people eat generally contain no or only a very small amount of cholesterol. Using this characteristic, some gutter oil can be identified, but the addition of gutter oil is also required to be above 10%.
Under the guidance of the teacher of Wuhan Institute of Technology, a graduate student named Wang Le once developed a blue test paper. With the increasing proportion of waste oil, the blue test paper will show yellow-green, light yellow and bright yellow. This is based on the "accumulation" of oil to detect the purity of oil. When there is sodium chloride (salt) in oil, its accumulation is large, otherwise it is small, while there is usually no sodium chloride in edible oil produced by formal channels. However, this method is also limited by the addition ratio of waste oil.
On the internet, you can find a company specializing in the production of "waste oil rapid detection kit". However, from the instructions provided by the company, "for some unpurified oils (such as sesame oil, pepper oil, etc.) and oils with other ingredients (such as Chili oil), this method is easy to produce false positives."
"The detection method of waste oil in the future must be a comprehensive evaluation method that integrates past experience." He Dongping said that a single method will not be included in the future Standard as a "classic method" for identification.
Government management is the key.
As a researcher engaged in oil research, He Dongping always believes that the treatment of waste oil is not determined by testing methods or standards, but the key lies in government management.
He once calculated that every 10,000 people can produce 1 ton of food waste every day, and these food wastes can produce 130 kilograms of waste oil after washing, distillation, decoloration and deodorization. When it is returned to the farmers’ market for sale, the price is half that of ordinary edible oil. Then the comprehensive statistical results show that the total profit of domestic gutter oil can reach 1.5 billion to 2 billion yuan a year.
However, in the treatment of kitchen waste, China has been in a state of "anarchy" for a long time, which provides a large-scale "gray industry" space for some unscrupulous traders. Therefore, He Dongping’s vision is that "the kitchen waste must be centrally purchased and treated by the government, and the waste oil must be eliminated from the source".
At the initiative of He Dongping, a kitchen waste treatment plant will be built in Wuchang, Hankou and Hanyang, three towns in Wuhan, from this year. While disposing of garbage, it can also produce 25 tons of biodiesel and 400,000 cubic meters of biogas every day.
"Economic benefits are second and social benefits are first." He Dongping said that as long as the city exists, these factories should exist. According to his vision, as long as more than 3,000 such factories are built in more than 600 cities across the country, it will not only alleviate the "garbage siege", but also completely solve the problem of waste oil.
In fact, relevant policies have been introduced in some areas of China. As early as 2006, Ningbo City, Zhejiang Province implemented the "Measures for the Management of Kitchen Wastes". According to the "Measures", the kitchen wastes in restaurants and canteens in Ningbo City will be collected, transported and disposed in a centralized and harmless way, so as to block the waste oil from the source. He Dongping visited Ningbo and found that the effect was remarkable.
Recently, enterprises have emerged in Beijing that use microbial fermentation technology to make kitchen waste into organic feed and organic fertilizer. These clean technologies have been favored by international venture capital institutions.
The Reuse Standard of Waste Oils in Urban Kitchen Wastes, which was formulated by He Dongping, a scientific researcher, is also expected to be published in 2011. "For example, in order to strengthen the management of the circulation field in the future, it is required that bulk oil must also be marked." He Dongping said. According to the scientist who has been engaged in cooking oil all his life, it may take about 10 years for China to completely ban cooking oil.
