Taking mad cow disease as an example, this paper expounds the homologous pollution mechanism of animal-derived feed, analyzes the feeding technology of kitchen waste and its homologous pollution, and puts forward that the feeding treatment technology should be carefully selected in the treatment of kitchen waste in China, and it is forbidden to feed ruminants with its feed products.
1 homologous pollution of food waste feed technology in recent years, with the development of economy, the increase of food waste output and the enhancement of public awareness of environmental protection, the food waste treatment industry has developed rapidly. At present, there are mainly three kinds of kitchen waste treatment technologies in China: aerobic composting, anaerobic digestion and feed, of which feed technology accounts for about 80%, occupying a dominant position. The kitchen waste is rich in protein, fat and various trace elements, which completely meets the basic requirements of being used as feed raw materials [1]. Nutrients such as protein and fat mainly come from animal-derived ingredients such as leftover meat, bones and eggs produced in food consumption. According to relevant research, protein and fat account for about 50% in some catering units in Beijing [2]. The feed product of kitchen waste is animal-derived feed containing various animal ingredients (animal-derived feed refers to a single feed made of animals or animal by-products [3]). When used as animal feed, it may cause homologous pollution, that is, a potential and uncertain risk of disease transmission caused by an animal eating animal-derived feed produced by similar animal tissues.
Study on homologous pollution of animal-derived feed The concern about homologous pollution of animal-derived feed originated from the outbreak of mad cow disease in Britain in 1985. In the study of mad cow disease, the researchers finally determined that the animal meat and bone meal of cattle and sheep and the feeding feed of cattle caused the emergence and spread of mad cow disease [4]. At present, the disease has broken out in Europe and America, and South Korea and Japan in Asia have also been affected, with more than 100 countries affected. Mad cow disease can also be transmitted to people, causing a neurodegenerative disease with high mortality-new Creutzfeldt-Jakob disease. Both mad cow disease and human creutzfeldt-Jakob disease are caused by a brand-new virus-prion protein (PrP). The biggest difference between prions and general viruses is that they contain no common genetic material-nucleic acid, and only consist of protein. Prions exist in two forms: prion protein (normal type, PrPc) and Nguyen virus (pathogenic type, PRPSC). The difference is only the tertiary structure of protein molecules. PrPc is a normal protein existing in organisms, but when organisms are infected with PrPsc, PrPsc can "force" normal PrPc to become pathogenic PrPsc. Because prions mainly exist in animal brain, spinal cord and other nerve cells, they can cause nervous system diseases such as mad cow disease [5]. Some scientists suspect that homologous pollution exists not only in cattle and sheep, but also in humans. Before 65438+1960s, the phenomenon of "cannibalism" was widespread among the Foer people in Papua New Guinea. In the later investigation, it was found that there was a kind of brain nerve disease similar to mad cow disease among Kulu people. The ancient Neanderthals also ate the same food. Some anthropologists believe that the spread of diseases such as mad cow disease is a possible reason for the extinction of Neanderthals [6]. In 2006, swine fever broke out in China. Although there is no evidence that it is caused by animal-derived feed, it is found that most of these pig farms use animal-derived feed, including pig blood and bone meal [7].
Homologous pollution analysis of feed treatment technology
3. 1 direct drying method The direct drying method is to heat the kitchen waste to a certain temperature after pretreatment (generally in the process of sorting, dehydration and deoiling) to achieve the effect of sterilization and drying, and obtain feed or feed additives through subsequent treatment. The typical process flow is shown in figure 1.
Figure 1 Typical process of drying kitchen waste to make feed.
The technical core of dry feed is high temperature drying and sterilization technology. The heating temperature and duration of different enterprises and heating processes are different, and the wet-heat method is generally slightly higher than the dry-heat method. Taking the wet-heat process in an enterprise as an example, the drying and sterilization temperature is 120℃ and the heating time is 30 minutes. According to related research, prions that cause mad cow disease cannot be completely inactivated in 134~ 138℃ high-pressure steam 18min [5].
The drying method mainly adopts physical methods, which does not change the types of animal substances such as cattle and sheep in kitchen waste, and high temperature can not guarantee to kill all pathogens. Therefore, there is a potential safety hazard of homology when the product is used as feed.
3.2 Biological treatment The technical core of biological treatment method is that microorganisms utilize the nutrients in kitchen waste and finally convert these substances into energy and substances needed for their own growth and reproduction. Its products are generally considered as protein feed composed of microorganisms themselves and their protein secretions. This technology mostly exists in the form of small biological processors, and generally the biological treatment time is short (within 1d). The typical family processing flow is shown in Figure 2.
Fig. 2 Process flow of microbial feed for kitchen waste.
According to this treatment process, the material changes of protein of animal origin, which mainly caused homology problems, were analyzed from the molecular biology theory, as shown in Figure 3.
Changes of protein substance in animals.
Therefore, by adding specific microorganisms with high protein content, the animal-derived protein in kitchen waste can be transformed into specific protein of microorganisms through a series of biological processes, thus changing the material properties and killing pathogens. This method is actually a combination of biological drying and biological fermentation. However, due to the complex composition of kitchen waste, short biological action time and limited biological proliferation conditions, there are still a large number of non-degradable ingredients derived from kitchen animals in the products, and there may still be the risk of homologous pollution when used as animal feed. ?
4 EU management requirements for animal-derived feed Since the cause of mad cow disease was determined, western countries such as Europe and America have made regulations on animal-derived feed, among which the requirements of the EU are the most stringent and detailed. Regulation No.1 of the European Parliament and the European Commission 1774/2002 stipulates: "After sanitary inspection, any animal-derived by-products unfit for human consumption shall not enter the food chain again." The regulation also pointed out that "scientific data show that feeding the same animal with homologous animal protein will have the risk of spreading diseases." As a preventive measure, the above practices should be prohibited. Therefore, detailed implementation rules should be formulated to ensure that animal by-products used for feeding are processed, stored and transported separately. If there is sufficient scientific basis, there should be room for feeding fish and fur animals with homologous animal proteins. "Article 22 of the Regulations stipulates:" It is forbidden to use products of animal origin (defined by the European Union as animal by-products and their processed products) under the following circumstances: ① feeding the same animal with homologous animal protein; (2) Feeding livestock other than fur animals with kitchen waste or feed containing kitchen waste; ③ Use organic fertilizer and soil improver in pasture instead of manure [8]. "As a preventive measure, the EU has completely banned the possibility of food waste feed products re-entering the human food chain.
5 Conclusions and Suggestions 1) Feed technology should be carefully selected for the treatment of kitchen waste. Feeding animals of the same kind with animal-derived feed has the risk of spreading diseases. Food waste in China may contain all edible protein of animal origin. In order to prevent risks, feed technology should be carefully selected in the treatment of kitchen waste. 2) It is forbidden to use kitchen waste to produce feed for ruminants such as cattle and sheep. Because mad cow disease, sheep itch and other diseases are more likely to spread and occur in ruminants, it is necessary to refer to the requirements of relevant laws and regulations and explicitly prohibit kitchen waste feed enterprises from producing such animal feed or feed additives. 3) Formulate the relevant management system of food waste feed production process and products. In order to minimize the possible risks of food waste feed products, it is necessary for the construction department and the agricultural department to cooperate with each other and formulate relevant management systems. The construction department focuses on the management of the production process, such as putting forward clear requirements for the drying and sterilization temperature and duration of the drying method, the fermentation time and conversion efficiency of the biological method, and enhancing the safety of the products; The agricultural department pays attention to the management of feed products, and puts forward requirements for product identification, flow direction, receiving unit and application scope, so as to avoid homologous problems as far as possible, especially to prevent these products from becoming feed for ruminants such as cattle and sheep.