1 Reasons for the production of aflatoxins
1.1 Sources of aflatoxins
Aflatoxins are toxic metabolites produced by Aspergillus flavus and Aspergillus parasiticus. As a storage fungus, Aspergillus flavus is widely distributed in nature. Aspergillus parasiticus is rare in my country. It is a parasitic pest of sugarcane or grapes in tropical and subtropical regions – water waxworm. In nature, the growth requirements of Aspergillus flavus are not high. Under aerobic conditions, peanuts and corn are the best breeding places. In the production process of aflatoxin, temperature is a very important condition. Too high or too low temperature has a great impact on the production of mold. At 25 ℃ ~ 30 ℃, it is easy to produce aflatoxin.
Aflatoxin is heat-resistant and can be completely destroyed by adding strong alkali and 5% sodium hypochlorite.
1.2 Causes of aflatoxin in feed
1.2.1 Ambient temperature and humidity The growth and reproduction of Aspergillus flavus requires certain temperature and humidity conditions, 25 ℃ ~ 30 ℃ is the optimum growth temperature, and the optimum relative humidity is 80% ~ 90%. It can be seen that the growth and reproduction of Aspergillus flavus is closely related to the climatic conditions of a certain area. From the point of view of many areas where mold poisoning occurs in feed, the southern region is higher than the northern region, because the temperature and humidity in the south are more suitable for the growth and reproduction of Aspergillus flavus, especially in the rainy season, Aspergillus flavus is easy to grow.
1.2.2 Moisture content of feed raw materials When the moisture content of corn, wheat, rice and other cereal feed raw materials is 17% to 18%, it is the optimum condition for the growth and reproduction of Aspergillus flavus. If the water content is too high after crushing, the grains are more suitable for the growth of Aspergillus flavus. Therefore, the moisture content of feed ingredients should be controlled below the mildew-proof moisture content.
1.2.3 Warehouse and pipeline pollution If the feed raw materials are stored for a long time or the warehouse is wet or leaking, and there is too much inventory without paying attention to ventilation, drying and cleaning, especially the crushed materials, due to their small particles, it is easy to absorb the surrounding moisture. It is likely to create a certain temperature and humidity for the growth and reproduction of Aspergillus flavus. Secondly, attention should be paid to the selection of cooling and supporting fans in the production of pellet feeds, otherwise it is easy to cause insufficient cooling time or insufficient air volume of the pellets, and the moisture and temperature of the feed will be too high, which will lead to the growth of Aspergillus flavus. In addition, the mold accumulation formed in the pellet lifting hopper or pipeline should be cleaned regularly.
1.2.4 Transportation Management. If the feed is not properly managed during transportation, rain, moisture, sun exposure, improper ventilation, and excessive stack pressure will also create favorable conditions for the production of aflatoxins.
2 Aflatoxin poisoning and its harm to humans and animals
2.1 Pathogenic mechanism of aflatoxins
Aflatoxin is resistant to high temperature and is difficult to be destroyed in the process of food/compound feed processing. When contaminated raw materials are used, food/compound feed is also contaminated, causing human and animal poisoning. The harm of aflatoxin to human and animal health is related to the inhibition of protein synthesis by aflatoxin. The bifuran ring structure in the aflatoxin molecule is an important structure for the production of toxins. Studies have shown that the cytotoxic effect of aflatoxin is to interfere with the synthesis of information RNA and DNA, thereby interfering with the synthesis of cellular proteins, resulting in systemic damage to animals. According to the research reports of relevant experts, aflatoxin B 1 can combine with tRNA to form adducts, and aflatoxin-tRNA adducts can inhibit the binding activity of tRNA and certain amino acids, and can inhibit the binding of essential amino acids in protein biosynthesis. For example, the binding of lysine, leucine, arginine and glycine to tRNA has different degrees of inhibition, thus interfering with protein biosynthesis at the translation level and affecting cell metabolism.
2.2 Aflatoxins and animal diseases
Aflatoxin poisoning mainly refers to the damage to the liver of animals, and the injured individual varies with animal species, age, sex and nutritional status. Studies have shown that aflatoxins can cause decreased liver function, reduce milk production and egg production, and make animals less immune and susceptible to infection by harmful microorganisms. In addition, long-term consumption of feed containing low concentrations of aflatoxins can also lead to intra-embryonic poisoning, and usually younger animals are more sensitive to aflatoxins. The clinical manifestations of aflatoxins are digestive system dysfunction, reduced fertility, reduced feed utilization, and anemia. Aflatoxins can not only reduce milk production in dairy cows, but also make milk contain transformed aflatoxins M1 and M2.
2.3 Aflatoxins and human health
Food hygiene is the primary issue of food safety. With the development of the world economy and the improvement of human living standards, people are paying more and more attention to the impact of food on human life and health. Among the contamination factors of food hygiene, the contamination of food by biological toxins is one of the most important contaminations, and aflatoxin ranks first in toxicity because of its severe damage to human and animal livers.
Aflatoxin is a highly toxic poison, and the median lethal dose of aflatoxin B 1 in animals is only 0.36 mg/kg body weight. Aflatoxins are 10 times more toxic than potassium cyanide. The poisoning caused by it mainly damages the liver, causing hepatitis, cirrhosis, liver necrosis and so on. Clinical manifestations include stomach discomfort, loss of appetite, nausea, vomiting, abdominal distension and liver tenderness. At the same time, aflatoxin is the strongest carcinogen found so far, its carcinogenicity is 900 times that of butter yellow, and its ability to induce liver cancer is 75 times greater than that of dimethyl nitramine.
The harm to human health from aflatoxins is mainly due to the consumption of food contaminated with aflatoxins. Prevention of this contamination is very difficult because the presence of fungi in food or food ingredients is widespread. The national health department prohibits the use of this seriously contaminated grain for food processing and production, and formulates relevant standards to supervise the implementation of the enterprise. However, it cannot be controlled for grains and foods containing lower concentrations of aflatoxins. Eating food contaminated with aflatoxins is positively associated with cancer incidence in developing countries. Research work by disease research institutes in Asia and Africa has shown that aflatoxins in food are positively associated with hepatocellular carcinogenesis. Eating foods with low concentrations of aflatoxin for a long time is the main cause of diseases such as liver cancer, stomach cancer, and colon cancer. In addition, aflatoxin and other pathogenic factors (such as hepatitis virus) have additive effects on the induction of human diseases.
3 Detoxification treatment
The lightly polluted feed materials can be used after detoxification treatment to make the toxin content meet the hygienic standards. The main detoxification methods are:
3.1 Removal method
It is mainly used to select mold particles, process and detoxify, and can be washed with water, soaked, or adsorbed by adsorbents such as activated carbon, bentonite, zeolite, diatomite or mannose oligosaccharide, and the detoxification effect is good. Detoxified diets with aflatoxin content of not more than 50 mg/kg can be used as pig feed.
3.2 Inactivation method
There are three commonly used methods, ① heat treatment method: although aflatoxin is stable to heat, it can also be partially decomposed at high temperature; ② alkali refining method: the principle is to destroy the lactone ring of aflatoxin to make it lose its toxicity, peanuts, corn This method can be used; ③ lime solution and salt detoxification, first soak the whole grain of corn contaminated with aflatoxin with lime milk water, soda ash water or plant ash water for 2 to 3 hours, then rinse with clean water until neutral, for two hours After drying, the detoxification effect can reach 60% to 90%.
4 Prevention and control measures
4.1 Pay attention to the management of raw materials
Try to choose feed crops that are not sensitive to mold: during harvesting, storage and transportation, try to avoid abrasion, crushing, rat bites, and insect bites, especially to avoid damage to the epidermis and shell of corn, peanuts and other grains. Broken peanuts are easily contaminated with Aspergillus flavus. The storage room should avoid excessive humidity, poor ventilation and stacking for too long.
4.2 Strengthen the procurement management of raw materials
The procurement of raw materials is the first hurdle for the quality of feed enterprises’ products. Therefore, procurement management is crucial. Efforts should be made to improve the overall quality of procurement personnel (such as raw material knowledge, raw material management knowledge, professionalism). Purchasing personnel should purchase raw materials in strict accordance with international standards and corporate standards. For raw materials that have been contaminated or may be contaminated by aflatoxins, they should not be purchased. Do not purchase unqualified raw materials at low prices and use them as shoddy ones. Purchasing personnel should strictly check the nutritional indicators and moisture content of raw materials. Especially the moisture content problem. Corn is the main raw material of finished materials, and the moisture content of corn directly affects the moisture content of finished materials. During the rainy season in the southern region, the moisture content of general raw materials should be less than 12.5%, and the moisture content of corn, sorghum, and rice should be controlled below 14%.
4.3 Strengthen the storage and storage of raw materials
The storage of raw materials is also an important issue. If the warehouse is leaking, dark, humid, or infested by mice, it is easy to promote the growth of Aspergillus flavus, thus affecting the quality of the product. In the storage of raw materials, we must pay attention to the control of air, humidity, temperature, etc., and strictly follow the “first in, first out” principle of use, and clean up the contaminated raw materials in time. The methods that can be used are: controlling the temperature of the storage environment, closed oxygen insulation storage, controlled atmosphere storage, low temperature ventilation storage and radiation method. For example, put the threshed wet corn into a sack lined with a plastic bag, fill and tie the bag mouth to inhibit the growth of Aspergillus flavus, and also add antifungal agents (such as propionic acid and its salts, sorbic acid and its salts) class, sodium diacetate, etc.).
4.4 Pay attention to the feed production process
The first is the humidity problem. my country has clear regulations on the moisture content of feed products: ①The moisture content of pig and chicken compound feed is not higher than 14% in the north, and not higher than 12.5% in the south. However, if the average temperature is below 10 °C in the season or the feeding period is not more than 10 days from the factory to the factory, or if a specified amount of antifungal agent is added to the compound feed, the moisture content can be increased by 0.5%; ② The moisture content of concentrated feed for pigs and chickens No more than 12 % in the north and no more than 10 % in the south. In the production of pellet feed: control the steam quality and the length of the steam pipeline to prevent the condensed water from entering the conditioner. Generally, the steam pressure should be controlled at 0.35 ~ 0.4MPa, and the moisture content should be controlled between 15% ~ 16%. ; Pay attention to the conditioning time, generally it should be controlled within 10 to 30 minutes, the moisture content of the powder after conditioning should not exceed 10%, or the difference between the moisture content after conditioning and before conditioning should be less than 0.5%; to choose a good cooling equipment , control the cooling time and cooling temperature; strictly test the water content of the feed before bagging.
The second is the temperature problem, pay attention to controlling the temperature of the steam (80 ℃ ± 2 ℃); pay attention to the cooling time and ventilation volume and the speculation on the temperature of the pellets after cooling, to prevent the material temperature from being too different from the room temperature, and the material temperature should be 3 ℃～5℃.
4.5 Do a good job in feed storage
The warehouse should be ventilated, cool, dry, clean and free of mold accumulation. Secondly, the stacking should be standardized, and a certain distance should be kept from windows and walls. If the storage time is long, it should be regularly turned for ventilation. Again is the use of mildew inhibitor. Now more propionate antifungal agents are used, such as Kemeiling, Chumoujing, Moudi 101, Lubaoxi, Wanlubao, Kemeiba, Lubaoxian, Lubaoxi NC, Wanxiangbao, etc. The usage method is as follows: 0.3% calcium propionate should be added to the granules with a moisture content of 12.5% to 13.5% in a sealed package and stored for more than 1 month. If the powder with moisture content of 11.55% to 12.5% is stored for more than 2 months, add 0.15% calcium propionate. Due to more rain in the southern region, it is best to add 0.2% to 0.4% calcium propionate or sodium propionate between March and May. In addition to propionic acid and its salts, sorbic acid and its salts, benzoic acid and sodium benzoate, formic acid and sodium formate, and calcium formate can also be used. At present, compound anti-fungal agents, such as Wanxiangbao and Kemeiba, are widely used in the world.
4.6 Safe transport of feed
When loading, make sure that there is no water or moisture in the car box. It is best to cover with rainproof appliances such as canvas during transportation, one can prevent rain, and the other can prevent sun exposure; when unloading, pay attention to the top layer of feed or Wet or torn bags are placed in the last pile for early use.