Xumu.com.cn 2004-9-24 China Animal Husbandry Network

This paper mainly expounds the physical and chemical characteristics of aflatoxin, its harm to animals and people, its residue in livestock products and its prevention and detoxification measures.

Aflatoxin; Harm; measure

Aflatoxin (AF) is mainly the metabolite of Aspergillus flavus and Aspergillus parasiticus. In warm and humid climate areas, aflatoxin may exist in food and feed contaminated by Aspergillus flavus and parasitic Aspergillus. Aflatoxin is most likely to pollute peanuts, corn, cottonseed, eggs, meat, milk and dairy products, followed by wheat, sorghum and sweet potato, and soybean meal is less polluted by aflatoxin. The contamination rate of grain and feed by aflatoxin in China is very high, which brings huge losses to feed enterprises and aquaculture owners. Eating food containing aflatoxin is harmful to human health.

Physical and chemical characteristics of 1 aflatoxin

At present, there are 18 kinds of aflatoxins with confirmed structures, such as AFB 1, AFB2, AFM 1 and so on. Their basic structures all contain difuranyl ring and oxanaphthone (also known as coumarin), the former is its toxic structure, and the latter may be related to its carcinogenicity. Aflatoxin is insoluble in water, hexane, ether and petroleum ether, but soluble in organic solvents such as methanol, ethanol, chloroform and dimethylformamide. The molecular weight is 3 12-346 and the melting point is 200-300℃. Aflatoxin is resistant to high temperature, usually not destroyed by heating treatment, and only decomposes at the melting point. Aflatoxin can decompose rapidly when it meets alkali, but this reaction is reversible, that is, it recovers under acidic conditions. Generally speaking, the temperature is 30℃, the relative humidity is 80%, and the grain moisture 14% or more (peanut moisture is more than 9%), which is most suitable for the propagation and growth of Aspergillus flavus. At 24-34℃, the toxin production of Aspergillus flavus is the highest. Almost all grains, forage grass and various foods (including livestock products) can be used as substrates for Aspergillus flavus.

2 Hazards of Aflatoxin

2. 1 the harm of aflatoxin to animals

Aflatoxin is very toxic, which is the most toxic among the molds found at present. Among the aflatoxins 18 found at present, AFB 1 is the most toxic, followed by AFM 1 and AFG 1, and AFB2, AFG2 and AFM2 are the least toxic. The toxicity of AFB 1 is 68 times that of arsenic, and its ability to induce liver cancer is 75 times greater than that of dimethylnitrosamine. Its toxicity varies with animal species, age, sex, physical condition and nutritional status, and young animals and male animals are more sensitive.

Aflatoxin can induce mutation, inhibit immunity and cause cancer. The target organ of aflatoxin is mainly the liver, and animal poisoning is characterized by systemic bleeding, digestive dysfunction and nervous system disorder. Acute poisoning is characterized by loss of appetite, dyskinesia, stop of excretion, hepatitis, jaundice, liver congestion, bleeding, swelling, degeneration and necrosis, accompanied by serious damage to blood vessels and central nervous system, and animals die within hours to days after poisoning. The early symptoms of chronic poisoning patients are poor appetite, weight loss, production performance decline, carcass and eggshell quality decline, jaundice, fatty liver, liver injury, animal immune suppression and late carcinogenesis.

pig

Pigs are sensitive to mycotoxins, especially suckling or suckling piglets. Generally speaking, when the level is relatively low, mycotoxins will reduce the feed intake, production performance and immune function. 20-200ppb aflatoxin B 1 can cause the decrease of feed intake and production performance, but it can be offset by increasing the level of special dietary nutrients such as lysine or methionine; Severe aflatoxin poisoning (1000-5000ppb) may cause acute effects, including respiratory effects. It is reported that when the content of aflatoxin in the feed is 2.0mg/kg, the weight of pigs can be reduced from 33.7kg in the control group to 29.7kg. Aflatoxin is transferred to the fetus through the placental barrier, causing fetal malformation, resulting in reduced litter size, weak litter, stillbirth and mummies. Individual female animals with acute poisoning will miscarry. Aflatoxin poisoning in boars shows decreased sexual desire.

poultry

Aflatoxin affects all poultry breeds, and high intake can lead to death, while low intake is harmful. Young birds, especially ducklings and turkeys, are very sensitive. Generally speaking, aflatoxin in growing poultry diet should not exceed 20ppb. However, feeding diets below 20ppb can still reduce the disease resistance and stress resistance of poultry. Laying hens can tolerate high levels of aflatoxin, but not more than 50ppb. AFB 1 mainly acts on the immune system, reducing the anti-stress ability of laying hens, reducing the egg weight, making the eggshell not hard and reducing the egg production. Feeding 2.0mg/kg aflatoxin to broilers can increase the mortality of broilers by 22.5%. Aflatoxin can destroy the sexual function of roosters, make testicular atrophy and seminiferous tubules stunted, and hinder the production of semen. It has been found that there are metabolites of aflatoxin in human egg yolk.

cow

Feeding aflatoxin contaminated feed not only reduces the production performance and physique of dairy cows, but also directly harms human health through aflatoxin M 1, a metabolite in milk.

beef cattle

Although the tolerance of beef cattle to aflatoxin is higher than that of pigs and poultry, aflatoxin still has a great influence on it. Eating aflatoxin contaminated feed for beef cattle will lead to a decrease in growth rate and an increase in feed-meat ratio. High levels of aflatoxin will not only cause liver injury in adult cattle, but also inhibit immune function. Calves can cause severe rectal spasm and proctoptosis in some cases. Acute poisoning of cattle can lead to death.

2.2 The harm of aflatoxin to human health

Aflatoxin is recognized as a carcinogen of liver cancer, among which AFB 1 is the most carcinogenic. People who eat foods with low aflatoxin content for a long time will suffer from liver damage. Recently, third world countries reported evidence of acute human aflatoxin poisoning. The comprehensive symptoms are vomiting, abdominal pain, pulmonary edema, convulsion, coma, brain edema and death, and excessive fat in liver, renal vein and heart. 1988 The International Agency for Research on Cancer (IARC) listed aflatoxin B 1 as one of human carcinogens, which has been proved by many Asian and African epidemiologists to have a positive effect on aflatoxin and hepatocellular carcinoma (LCC) in the diet. In addition, the carcinogenic effect of human aflatoxin may be related to age, sex, nutritional status, hepatitis or parasitic infection. Shank et al. (1972) investigated the food sold in the Thai market and cooked food (meals) at home, and calculated the average daily intake of aflatoxin per person. The results showed that the content of aflatoxin was consistent with the regional distribution of liver cancer incidence. Aflatoxin pollution of Philippine corn and homemade peanut butter is serious. In an area where corn is the staple food and another area where homemade peanut butter is often eaten, the incidence of liver cancer is more than 7 times higher than that in other areas. Among the residents who eat peanut butter, the metabolite of aflatoxin in urine after eating peanut butter was determined as M 1, and aflatoxin b11.2-6544 was ingested through peanut butter every day in 7 areas.

2.3 Residue

Aflatoxin is most distributed in the liver after being ingested by animals, and its content can be 5- 15 times that of other organs and tissues. It can also be detected in kidney, spleen and adrenal gland. There is a very small amount in blood, which is generally not detected in muscle. Aflatoxin will not accumulate in the body if ingested intermittently. Aflatoxin and its metabolites remain in animals and are excreted with milk, urine, feces and breath.

Experiments show that aflatoxin B 1 and its metabolites can be detected in liver, kidney, muscle, blood, milk and eggs after animals ingest aflatoxin B 1, thus causing the pollution of animal food. Aflatoxin B 1 about 1% ingested by mammals is discharged into milk and urine in the form of M 1. It was found in milk that the concentration of M 1, 12-60 hours was the highest after cows ingested AFB 1 1 hour, and decreased to a trace after 5 days. Guangxi health and epidemic prevention station fed 12 cows with different contents of AFB 1 for 36 days to study the transformation relationship of AFB 1 in cattle. The results showed that the residue of AFB 1 in dairy cows generally accounted for 3.45%- 1 1.39% of the total intake of AFB 1. Agacdelen( 1993) reported that when laying hens were fed AFB 1500μg/d, AFB 1 was 0. 1 17PPb, AFB 1 was not detected in eggs after 4 days of feeding suspension.

Little information is available about the toxin residues in animal products for human consumption, and some data are summarized in Table 4. In different countries, the mandatory maximum limit of aflatoxin M 1 is 0.05- 1PPb, and aflatoxin B 15PPb. In most countries, it is acceptable to detect toxins below this level. The standard of aflatoxin in food in China is being formulated.

3 Preventive measures

3. 1 mildew prevention is to prevent raw materials and products from being contaminated by mold and its toxins, and to prevent toxic mold pollution is the key to prevent AF. The main anti-mildew measures are as follows:

3. 1. 1 Controlling moisture refers to controlling the moisture of raw materials such as grain and feed and the relative humidity of storage environment. (1) Strictly control the moisture content of raw materials such as grain and prevent the mildew of raw materials such as grain, which must be started when grain is harvested in the field. The key is to dry quickly after harvest, so that the water content of grain can be reduced to a safe range in a short time. Generally, the moisture content of grain is below 13%, that of corn is below 12.5%, and that of peanut is below 8%, so molds are difficult to reproduce. The moisture content of plant cake, fish meal and meat and bone meal shall not exceed 12%. ⑵ Strictly control the water content of feed. When the water content of feed exceeds 15%, mold can grow and multiply in large quantities. When it reaches 17- 18%, it is the best condition for fungi to produce toxins. According to China's regulations, the water content of pig and chicken compound feed should not exceed 14% in the north and 12% in the south. The water content of concentrated feed for pigs and chickens should be lower than 12% in the north and 10% in the south. Generally speaking, the moisture content of granular materials should be controlled at 12.5%, and the moisture content of powder should be lower than 12%. ⑶ Strictly control the moisture in the production process, control the quality of steam added in the feed processing process, the length of conveying pipeline, the temperature and pressure of regulator, the structure of cooler and cooling temperature, so as to control the moisture in feed. (4) Strictly control the relative humidity of raw materials and finished products storage warehouses. Before storing grain, the warehouse should be kept clean and dry, the bulk warehouse should have ventilation equipment, and the closed warehouse should make the external humidity not affect the grain in the warehouse.

3. 1.2 The ideal storage condition for low-temperature storage is to store grain in a dry and low-temperature state. The temperature is below 65438 02℃, which can effectively control mold reproduction and toxin production. Raw materials and finished products with high moisture content should be stored at low temperature. For example, when the water content of rice is 12%, it can be stored at 35℃, while when the water content reaches 14%, it is safe to store it within 20℃.

3. 1.3 Reduce damage and destroy damaged seeds. Broken raw materials are easily contaminated by mold from wounds. Therefore, in the process of harvesting and storage, we should minimize the damage of seeds, avoid pests, rodents and grinding, and prevent surface damage such as grains and peanuts; Remove damaged seeds.

3. 1.4 carbon dioxide gas preservation method Most molds are aerobic, and they cannot grow and reproduce without oxygen. Therefore, grains can be stored in a closed container filled with carbon dioxide gas for several months without mildew. At the same time, this method also has the function of preventing insects. Silage mainly prevents corruption by eliminating oxygen.

3. 1.5 Feed raw materials and compound feeds processed in humid and high-temperature seasons are easy to get moldy when coated with mildew inhibitor in time, and the shelf life can be prolonged by applying mildew inhibitor. Commonly used fungicides mainly include propionic acid or its salt, sorbitol and its salt, sodium diacetate, fumaric acid and so on. Propionic acid and its salts (sodium propionate and calcium propionate) are the most widely used. In addition, some antimildew agents (such as sodium diacetate) can also improve feed utilization and palatability, and silage additives (such as liquid ammonia, propionic acid, microbial culture or enzyme silage) are beneficial to prevent mycotoxins.

3. 1.6 Try to shorten the shelf life. Feed raw materials and feed should adopt the principle of first in first out, and the shorter the time, the better; It is best not to prepare feed for more than three days to avoid being contaminated and propagated by mold for a long time.

3. 1.7 Keep the air and dust of the equipment containing mold spores clean. So the warehouse and all production and transportation links should be kept as clean as possible.

3. 1.8 Breeding of resistant or toxin-producing crop varieties The mildew resistance of selected crops is related to genetic factors. Cultivating and selecting resistant or toxic crop varieties can provide a simple and effective way to control aflatoxin pollution by using their own resistance.

3. 1.9 radiation mildew prevention The use of radiation can not only prevent mildew, but also improve the freshness of feed and grain. The grain and feed irradiated by 1× 106Radγ-ray by the Institute of Atomic Energy of the US Department of Agriculture will not be moldy even if stored at 30℃ and relative humidity above 80% for 45 days.

3.2 After the detoxified feed is contaminated by mold and mycotoxin, it should be destroyed and removed. The method is as follows:

3.2. 1 Aflatoxin contaminated grain is unevenly distributed, mostly on damaged, moth-eaten and discolored particles. If these are removed, the toxin level will be reduced. Observe feed and grain by sight and smell, and judge whether it is polluted or not. If it is seriously polluted, it should be eliminated. The silage of ruminants should be carefully checked when feeding, and if mildew is found, it should be removed.

3.2.2 Ultraviolet rays or gamma rays by radiation method can effectively kill mold and destroy the chemical structure of aflatoxin, thus achieving the purpose of detoxification. The detoxification rate of high-pressure mercury lamp ultraviolet irradiation can reach 97-99%. Feng Dingyuan (1995) reported that aflatoxin B 1 decreased by 42.3 1%, and G 1 and G2 were almost completely removed after being exposed to natural sunlight for 30 hours.

3.2.3 Water washing method is insoluble in water and stable to heat. The distribution of aflatoxin in corn and other crops is very uneven, and the total amount of aflatoxin in epidermal embryos can reach more than 80%. Water washing method uses the difference of specific gravity between corn germ and milk germ to remove the ground germ or epidermis floating on the water. The results of laboratory and application show that the average detoxification rate of this method can reach above 80%. Most of the peanuts contaminated by AF have a light specific gravity, and most of the peanuts floating in the water are AF-contaminated nuts. This method can remove 88% of the contaminated grains.

3.2.4 Adhesive method At present, the efficacy of the adhesive used to bind aflatoxin B 1 in vitro has been affirmed. The main binders are calcium sodium aluminosilicate (HSCAS), clay, zeolite, bentonite, activated carbon, montmorillonite and other binders. But the binding effect of HSCAS in vivo is the same as that in vitro. In order to achieve good adhesion effect to aflatoxin, the minimum requirement for adhesive is porous, and its pore size is in the range of 0.015-0.090 mm (150-900a). Lindemann et al. (1993) reported that adding 0.25% or 0.5% bentonite sodium to the diet containing AFB 1 800μg/kg could improve the average daily gain and average daily feed intake of piglets.

3.2.5 Chemical Drugs Detoxification Some chemicals, such as hypochlorous acid, sodium hypochlorite, hydrogen peroxide, ammonia water, sodium hydroxide, etc., have certain effects on clearing atrial fibrillation. Feng Dingyuan et al. (1997) reported that peanut cake was treated with 0.25%, 0.50% and 1.0% sodium hypochlorite for 24, 48 and 72 hours respectively. There was no significant difference in detoxification effect among the groups, and the total amount of aflatoxin decreased by more than 93%, but the effects on aflatoxin were different, among which aflatoxin B65433. Ammonia treatment is to treat corn, soybean meal and peanut meal contaminated by aflatoxin with ammonia or ammonia water. Under the action of ammonia, the lactone ring of toxin can be cracked to achieve the purpose of detoxification.

3.2.6 metabolic detoxification Method This method screened some microorganisms and used their biotransformation to destroy or transform mycotoxins into low toxic substances. Reported microorganisms such as Rhizopus, Rhizopus, Aspergillus Niger and Bacillus subtilis have good removal effect on aflatoxin.

3.2.7 Adding Sulfur-containing Amino Acids Methionine and Cysteine are added to the feed. Sulfur atoms in livestock and poultry can promote the synthesis of glutathione (GSH) under the action of enzymes in vivo, and GSH can resist toxic substances in vitro. Hulan et al. (200 1) reported that on the basis of oral administration of AF2mg.kg- 1 to broilers, methionine 0.2 g.kg- 1 and cysteine 0.4g.kg- 1 were added respectively, which could maintain the same level of red blood cells and white blood cells as the control group.

3.2.8 With mixed dilution method, if the raw materials and feed contaminated by mold exceed the specified value, it can be diluted with unpolluted raw materials and feed to make mycotoxin within a safe range, but the dilution should be uniform. After dilution, it is necessary to prevent the mold from growing and polluting again, and prepare the feed as soon as possible. This method is suitable for farms.

3.2.9 Adding vitamin C can block the epoxidation of aflatoxin B 1, thus preventing it from being oxidized into active toxic substances. Adding a certain amount of vitamin C and an appropriate level of amino acids to the diet is an effective way to overcome aflatoxin poisoning. Hu Shaochang (200 1, translated) in the experiment of aflatoxin B 1 and aflatoxin B 1+ vitamin C in broilers, the former led to the immune failure of infectious bursal disease in chickens.