What Are Aflatoxins?

Aflatoxin (AFT) is a bisfuran toxoid produced by certain strains such as Aspergillus flavus and Aspergillus parasiticus. There are about 20 kinds of derivatives, named B1, B2, G1, G2, M1, M2, GM, P1, Q1, poisonous alcohol and so on. Among them, B1 is the most toxic and the most carcinogenic. After animals eat aflatoxin-contaminated feed, trace amounts of toxins can be detected in liver, kidney, muscle, blood, milk and eggs. Aflatoxin and its producing bacteria are widely distributed in nature. Some strains produce more than one type of aflatoxin, and there are also strains that do not produce any type of aflatoxin in aflatoxin. Aflatoxins mainly contaminate grains, oils and their products, and various plant and animal foods can also be contaminated. ^[1]

In 1993, aflatoxin was classified as a class of naturally occurring carcinogens by the World Health Organization (WHO) Cancer Research Institute, and it is a highly toxic highly toxic substance. ^[2]

Chinese name: Aflatoxin
Foreign name: aflatoxin
derivative: B1, B2, B2a, G1, G2, G2a, M1, M2, P
Producing bacteria: Certain strains such as Aspergillus flavus and Aspergillus parasiticus

Nature: Is a class of compounds that both contain difuran rings and coumarins
testing method: Thin layer chromatography and high pressure liquid chromatography
Removal method: Adsorption, radiation treatment, alkali treatment, enzymolysis, etc.
Short name: AF

AF Aflatoxin AF Overview

Aflatoxin Introduction

The occurrence of "turkey X disease" (named after the unknown cause at the time) in the suburbs of London, England, in 1960 led to the discovery of AF (aflatoxin). AF is a class of fungal secondary metabolites with similar structures and physical and chemical properties, and is the most stable type of mycotoxins that has been found in nature. ^[3]

It is a class of compounds that both contain a difuran ring and a coumarin (oxanthinone). Aflatoxin produces fluorescence under long-wave ultraviolet light, and is named B1, B2, G1, G2, M1, M2, P1, R1, GM, and poison alcohol according to the fluorescence color, RF value, and structure. Among them, B1 has the highest yield, the highest toxicity, and the strongest carcinogenicity, followed by G1 and M1. The content of AF in the sample can be determined by the fluorescence detection amount shown by thin layer chromatography ^[4] . It was discovered in 1961 that the peanut cake contaminated by Aspergillus flavus can induce liver cancer in rats. In 1962, aflatoxin was identified and proved to be a strong carcinogen. In the structure, the aflatoxin with a double bond at the end of the difuran ring easily forms epoxidized metabolites and increases its toxicity, carcinogenicity and mutagenicity. Aflatoxins mainly contaminate grains and oils and their products, such as peanuts, peanut oil, corn, rice and cottonseed. Aflatoxin B1 is used as a contamination indicator in domestic food testing, and can be detected by thin layer chromatography and high pressure liquid phase method. ^[5]

Aflatoxin and its producing bacteria are widely distributed in nature. Some strains produce more than one type of aflatoxin, but there are also strains that do not produce any type of aflatoxin in aflatoxin. Aflatoxins can be detected in the seeds and processed products of cereals and oil crops, dried and fresh fruits, condiments, tobacco, milk and dairy products, meat, fish and shrimp, and animal feeds. Peanuts and corn are the most contaminated. AF can be transferred to the animal's milk, liver, kidney, and muscle tissues through food. AF is a hyper-toxic substance, of which B1 is currently the most carcinogenic of known carcinogens, can induce liver cancer in animals, and can cause acute poisoning and death in some animals. The United Nations World Health Organization (WHO) and FAO (FAO) in 1975 set the maximum allowable content of AFB1 in food to 15 ppb, and governments of various countries have formulated sanitary standards and inspection regulations for the maximum allowable amount of AF in food and feed. The most important environmental factors affecting the production of AF are temperature and moisture. The suitable temperature range for Aspergillus flavus to grow and produce is 12 ~ 42 , the optimal temperature is about 33 , the minimum relative humidity is 78%, and the optimal relative humidity is 98%. The moisture content is more than 18%, and the peanut moisture content is more than 10%. Under aeration conditions, Aspergillus flavus can grow rapidly and produce poison. Adopting low temperature, drying, deoxidizing, and chemical agents to preserve food and feed can effectively prevent the growth and toxicity of Aspergillus flavus. For food and feed containing aflatoxin, physical, chemical and biological methods can be used to detoxify, such as mechanical, electronic and manual methods to select broken toxin-containing peanuts; improve processing accuracy can be removed from grain Toxins in the grain cortex and seed germ; high temperature and high pressure treatment can convert AF into non-toxic compounds; adsorption with activated clay and activated carbon can remove AFT in vegetable oil; treatment with strong alkali or oxidant can cause chemical changes in AFT and Detoxification; Tests show that a few bacteria, molds, and actinomycetes have the ability to transform aflatoxins. ^[4]

AF Physicochemical properties of aflatoxin AF

Although there are many types of Aspergillus flavus, they all have difuran rings and oxonaphthone (also known as coumarin) in their basic structure. The former is its toxic structure, and the latter may be related to its carcinogenesis. AFT is difficult to dissolve in water, hexane, ether and petroleum ether. It is easily soluble in organic solvents such as methanol, ethanol, chloroform, acetonitrile and dimethylformamide. It has a molecular weight of 312 to 346 and a melting point of 200 to 300 ° C. AF is stable to light, heat, and acids, and is resistant to high temperatures. Usually, heat treatment does little damage to it. Decomposition occurs only at the melting point. It is very stable in neutral and weakly acidic solutions, slightly decomposed in acidic solutions with a pH of 1 to 3, and rapidly decomposed and destroyed in a solution with a pH of 9 to 10. AFT can decompose quickly when it meets alkali. When pH is 9 ~ 10, AFT decomposes into almost non-toxic salt quickly, but the reaction is reversible, that is, it recovers under acidic conditions. Therefore, this chemical reaction can be used in food detoxification. Pure toxins are stable at high concentrations, and pure toxins at low concentrations are easily broken down by UV radiation. 5% sodium hypochlorite solution, Cl ₂ , NH ₃ , H ₂ O ₂ and SO ₂ can all react with AFT to destroy its toxicity. Under natural conditions, the stability of AF contaminated in food is very strong. AFB1 seriously contaminated rice has been naturally stored at room temperature for more than 20 years, and its toxic content has gradually decreased, but AFB1 can still be detected. ^[3]

AF Structure of aflatoxin AF

Chemically, aflatoxin is a highly substituted coumarin. Of which AFB1 is methoxy and difuran

A combination of cyclo, coumarin, and cyclopentenone. AFG1 structure is methoxy, difuran ring, coumarin and cyclic lactone. In the natural environment, only AFB1, AFB2, AFG1, AFG2, AFM1, and AFM2 were detected in contaminated food. Among them, AFB1 is the largest and most toxic. AFM1 is a metabolite of AFB1, and its toxicity is second only to AFB1. ^[2]

The order of toxicity of various metabolites of aflatoxin is: AFB1> AFM1> AFG1> AFB2> AFM2> AFG2. It can be seen from the toxicity sequence that the structure of the double furan ring has a double bond structure at the end

The toxicity is high, and the toxicity without double bond structure is relatively small. ^[2]

AF Aflatoxin AF production conditions and distribution

AF Aflatoxin AF production

The production of AF requires certain conditions. Toxicity of different strains varies greatly. Except the substrate, temperature, humidity, and air are all necessary conditions for AFT growth and reproduction. Researchers have found that the optimal growth conditions for AF and Aspergillus parasiticus are 33 to 38 ° C, pH is 5.0, and Aw (water activity) is 0.99. The temperature is between 24 and 28 ° C, and the relative humidity is above 80%. Therefore, AF poisoning is prone to occur in the spring and summer in the south and warm and humid regions, and some crops may be polluted by AF even before or during harvest. ^[3]

AF Aflatoxin AF distribution

AF is often found in soil, flora and fauna, various nuts, especially peanuts and walnuts. AF is also frequently found in soy, rice, corn, macaroni, condiments, milk, edible oil and other products. Generally in tropical and subtropical areas, the detection rate of AF in food is relatively high. The total distribution in China is as follows: There are many virus-producing strains in Central China, South China, and North China. ^[3]

AF Aflatoxin AF toxicity and harm

AF Mutagenicity of aflatoxin AF

Aflatoxin is mutagenic, and can cause unscheduled DNA synthesis in human fibroblasts. Animal experiments show that chromosomal aberrations, chromosome breaks, and deletions of some chromosomes 4q, 13q, and 14p. AFB1 is a mutagenic compound that can cause changes in the genetic material of the organism, but AFB1 itself cannot cause mutations. It must be metabolized and activated in the body to have a mutagenic effect, which is called an indirect mutagen. AFB1 is activated by a liver microsomal enzyme into an electrophile, namely AFB1-2,3-epoxide. The second carbon of this epoxide is combined with the guanine ketone group of DNA to form AFB1-DNA adduct. In addition, The metabolites AFM1 and AFP1 of AFB1 can also be converted into electrophiles and bind to DNA. The AFB1-DNA adduct undergoes a purine-removing reaction to form AFB1-N7-guanine, which causes a gap in the purine-free position of the DNA molecule, which causes damage. ^[2]

At present, it is believed that both the damage caused by DNA depurination and the change in DNA molecules caused by the continuous accumulation of ring-opening adducts through acid and alkali hydrolysis are changes before mutation and have the possibility of further development into cancer. . ^[2]

Aflatoxin harm to the liver

Aflatoxin is a highly toxic hepatocarcinogen. Among them, aflatoxin B1 can cause cells to repair DNA by mistake, cause serious DNA mutagenesis, and can also inhibit DNA and RNA synthesis, thereby inhibiting protein synthesis. From the epidemiological survey of liver cancer in China, it was found that the level of aflatoxin in the diet of some populations was positively correlated with the incidence of primary liver cancer. Experts surveyed other regions with a high incidence of liver cancer and reached the same conclusion. Hepatitis B virus and aflatoxin B1 are two major risk factors for liver cancer in China. Experts in oncology have established experimental models of the mechanism of liver cancer caused by hepatitis B virus and aflatoxin B1, and used these models to find separate HBV genes. It does not induce liver cancer in mice, but the hepatitis B virus gene can enhance the carcinogenic effect of aflatoxin B1. Both can make liver cells in a more proliferative state and have a significant synergistic effect in the process of causing liver cancer. ^[2]

The occurrence of cancer is the result of accumulation of genetic changes. Scientists have confirmed that the p53 gene is a suppressor gene for cancer. The mutation of the p53 gene is the material basis for the development of many tumors. Many people may be affected early in life (about 5 years old). The attack of hepatitis B virus and aflatoxin, and the deletion or mutation of certain genes in the human body cause mutations in the p53 gene, which in conjunction with other factors eventually lead to canceration. ^[2]

Aflatoxin toxicity

Since the aflatoxin was isolated in 1962, people have conducted in-depth research on its toxicity, and found that its toxicity is extremely toxic, and its severe toxicity is 10 times stronger than the well-known potent poison potassium cyanide, which is 10 times stronger than cobra and gold. The venom of ring snakes is even more toxic, 28-33 times more toxic than the highly toxic pesticides 1605 and 1059. A severely moldy corn containing 40 g of aflatoxin can poison two ducklings. Beijing Medical University once fed rats with aflatoxin containing 20 g / kg of liver cancer for one year. It has been reported abroad that cancer can be induced when AF is 1 g / kg. ^[2]

Aflatoxins have strong acute toxicity and significant chronic toxicity. After ingestion of a large amount of aflatoxin in humans, acute lesions such as hepatic parenchymal cell necrosis, bile duct epithelial cell proliferation, liver fat infiltration, and liver hemorrhage can occur. The early symptoms are fever, vomiting, anorexia, jaundice, and then ascites, lower limb edema, and Died soon. Poisoning incidents caused by aflatoxins have been reported at home and abroad. Among them, the poisoning incident in India in 1974 was the most serious: more than 200 villages in the two states of western India used corn as a staple food. Due to excessive rain that year, As a result of severe mildew of corn, 397 people were poisoned and 106 people died after eating moldy corn. Autopsy and pathological experiments proved that the poisoning incident was caused by aflatoxin B1 poisoning. Chronic toxicity is manifested as growth disorders, subacute or chronic damage to the liver, weight loss, and liver cancer. ^[2]

Food contamination with aflatoxins

In 1972, 1973, 1974, and 1981, China carried out a general survey of AFB1 in foods throughout the country, and found that the contamination of aflatoxins varies by region and food type. The aflatoxin pollution in the Yangtze River and the south of the Yangtze River is serious, and the pollution in the northern provinces is light. Among various types of food, peanuts, peanut oil, and corn are the most contaminated. Rice, wheat, and flour are less contaminated, and legumes are rarely contaminated. Some experts and scholars investigated the aflatoxin contamination in grains, oils, and foods in Guangxi, Jiangsu, Hebei, Beijing, and other places in China in 1992. The results showed that except for the high pollution rate of peanut samples, which reached 55.6%, the corn The contamination rate is only 15.6%, and the level of contamination does not exceed the current standard for aflatoxin B1 in foods in China. ^[2]

Aflatoxin contamination in foods has spread to various regions of the world. Generally speaking, tropical and subtropical regions have more serious food contamination. Among them, peanuts and corn are the most contaminated. Survey results from 12 countries in the 1960s and 1980s It shows that the positive rate of peanut is 0.9% -50%, the average toxic content is 25-1000ng / g, the highest toxic sample is 25000ng / g, the positive rate of corn is 3.5% -73%, and the average toxic content It is 5 400ng / g, and the highest toxic content is 12500ng / g. ^[2]

In view of the toxicity of AF, currently more than 60 countries in the world have established maximum limits for aflatoxins in food and feed and corresponding regulations. China also promulgated the "Administrative Measures for the Prevention of Food Contamination by Aflatoxin" on November 26, 1990. The management measures stipulate: in order to ensure the health of infants and young children, the food department shall provide food for which no aflatoxin can be detected, and when using food, oilseeds and oil products containing aflatoxins that exceed the allowable amount standard, it must be effective in the process Measures are taken to eliminate toxicity, and the product is ready for consumption after meeting the standards. Violations will result in legal liability. ^[2]

AF contamination causes food spoilage. Food is contaminated and its edible value is reduced. It is even inedible. Virginia Virginia Asia has tested 500 corn samples in 5 years. About 25% of corn samples contain toxins. Human consumption of foods contaminated with AFT can cause acute poisoning, cause liver necrosis and bleeding, and chronic poisoning can cause liver cancer. At the same time raising livestock and poultry with contaminated feed will reduce the productivity of livestock and poultry, slow down weight gain, and indirectly cause major harm to humans. ^[3]

Economic effects of aflatoxin

The World Food Organization (FAO) estimates that 25% of food crops are affected by mycotoxins, mainly AFT. AFT can cause livestock deaths, reduced growth rates, and reduced feed utilization. AFT can also reduce the yield of food and fiber crops. Because countries have established corresponding AFT allowable standards and regulations, this will have a certain impact on trade. For example, the European Union has repeatedly refused to import peanuts and their products on the grounds that AFT exceeded the standard. ^[3]

AF Aflatoxin AF Absorption and Metabolic Intervention

Once aflatoxin is ingested, there are two ways to reduce the toxicity and carcinogenicity of aflatoxin in the body. ^[6]

AF Aflatoxin block reduces AF absorption

Probiotics can adsorb aflatoxin and form a bacterial cell-AF complex, which reduces the absorption of aflatoxin in the intestinal tract, and the microorganisms are discharged together with aflatoxin. Humic acid is an organic polymer compound that has strong adsorption on heavy metals, aromatic compounds, and minerals. Studies have shown that humic acid extracted from bituminous coal has a strong adsorption effect on AFB1. Chlorophyllic acid and AFB1 combine to form a strong molecular compound, which affects the absorption of AFB1 and reduces the biological activity of ingested carcinogens. Studies have shown that glucomannan and its complex with inorganic adsorbents have relatively good adsorption effects on aflatoxins at room temperature. The mechanism is that mannan oligosaccharides can react with hydrogen bonds, ionic bonds, and hydrophobic forces. Aflatoxins produce adsorption, which is dominated by physical effects. ^[6]

AF Aflatoxin regulates AF metabolism in vivo

Studies have found that many traditional Chinese medicines and their active ingredients can act on the drug metabolism enzyme system, and then affect the metabolic activation and detoxification of aflatoxins, such as Huangcen, Danshen, curcumin, flavonoids, polyphenols, etc. The mechanism of pyrithione's resistance to aflatoxin is not only to reduce AFB1-8,9-epoxy compounds, but also to increase the activity of GST, promote the binding of glutathione to AFB1-8,9-epoxy compounds, and increase AFB1-sulfur. Alcoholic acid adducts are excreted through the urine. ^[6]

AF Aflatoxin AF detection method

The detection method of AF has mainly developed from thin-layer chromatography to high-performance liquid chromatography, micro-column method, and enzyme-linked immunosorbent method, and has been widely used. Its progress and new chemical detection methods and new instruments The appearance of is inseparable. The rapid application of these new methods and new methods provides a wider range of choices for the detection of aflatoxins and adapts to different detection purposes and requirements. ^[3]

Aflatoxin thin layer chromatography

Thin layer chromatography (TLC) is a classic method for the determination of AF. The principle is that after the sample is extracted, column chromatography, eluted, concentrated, and separated by thin layer, it produces blue-violet or yellow-green fluorescence under ultraviolet light of 365nm , And determine its content based on the minimum detection amount shown on the thin layer. ^[3]

Aflatoxin high performance liquid chromatography

HPLC has the advantages of high resolution and short analysis time. Its principle is that several compounds to be separated in the sample solution have different distribution amounts between the mobile phase and the stationary phase, thereby achieving the purpose of separation. AF is electrochemically derivatized after the column to emit characteristic fluorescence, which is detected after being captured by a fluorescence detector. Finally, the data is processed by a ChemStation. This detection method combines chemical analysis tests with leading computer technology, which greatly improves the degree of automation, and can test more samples while the test space, manpower, and instruments remain unchanged. HPLC is a method developed in recent years for the detection of AFB1, mainly using a fluorescent detector. This method is fast and accurate, but it requires expensive equipment and has not been widely used. ^[3]

Aflatoxin microcolumn method

The determination of AF by the micro-column method is to use a silica-magnesium adsorbent in a micro-column tube to adsorb AF and show fluorescence under ultraviolet light at 365 nm. Its intensity is directly proportional to the AF content at a certain concentration, so that AF can be briefly quantified. ^[3]

Aflatoxin ELISA

Enzyme-linked immunosorbent assay (ELISA) is a specific immunological reaction between the antigen (or antibody) adsorbent and the antibody (or antigen) labeled with the enzyme and the test object (antigen and antibody) in the sample. The method to increase the sensitivity of the assay is a qualitative or semi-quantitative method. There are roughly two methods for detecting AF: one is the double-antibody sandwich method; the other is the competitive method. The kit, supporting instruments and methods for immunosorbent assay are listed in the national standard (GB / T5009 22-1996 second method). ^[3]

There are also more reports on the detection of AFB1 by enzyme-linked immunoassay. Currently, there are more mature ELISA kits for detecting mycotoxins such as AFB1 in food and feed. There are also some ELISA detection foods in China since the 1990s. And research report of AFB1 in feed. ^[3]

Aflatoxin other methods

(1) Brominated Fluorescence Spectrophotometry (SFB)

After the sample was extracted with a methanol-water mixed solvent, part of the extraction solution was subjected to solid-phase separation for pre-column treatment. 500 L of the purified extraction solution was derivatized with a bromine reagent, and then detected by a fluorescence detector. The absorbance comparison can be directly converted into the total content of AF. The law has been certified by AOAC and the USDA Federal Grain Inspection Center. ^[3]

(2) Hyperspectral method (HS)

Hyperspectral method is a non-invasive and non-destructive imaging technology based on reflected energy. It is used in agricultural product detection to quickly provide chemical and other internal details of the product. According to research reports, training wasps can be used for AF detection. Since AF is mainly produced by Aspergillus flavus, the parasitic wasp can identify the existence of the target odor by training to associate the odor of Aspergillus flavus with sugar water and have a differential behavioral response to these odors. This training response is being applied to the AF monitoring and detection practice of stored corn and peanuts, and no relevant result evaluation has yet been given. ^[3]

Comparison of Aflatoxin Methods

Thin-layer chromatography is cumbersome for sample processing, the experimental process is complicated, it takes a lot of time, and it is susceptible to impurities. It is more suitable for the qualitative detection of AF. It is the main method used in the early research of AF. In the future, although the thin layer chromatography method is continuously improved and can be completed in general laboratories, it will still be limited to a certain extent in its application due to its complicated pre-treatment process. ^[3]

High-performance liquid chromatography for the determination of AF requires a high level of technology. At present, this method is used to detect AF. However, the chemical agents and processing methods used in a specific experiment are very different, which affects the accuracy of the experimental results. The method should be further improved in practice. However, in general, high-performance liquid chromatography is relatively simple to operate, and can detect multiple AF types at the same time, which is suitable for the analysis of large quantities of samples. Combining the application of immunoaffinity columns with high-performance liquid chromatography is one of the more widely used methods, and it will be widely used in the future. ^[3]

The micro-column method for AF is mainly used to check the presence of AF and to quickly screen out the over-standard samples. To distinguish and quantify the types of AF, different AF components need to be separated and then detected by other methods. Therefore, the micro-column method cannot complete the entire AF detection process, and is only suitable for qualitative inspection. ^[3]

Enzyme-linked immunosorbent assay is simple and safe to use, but due to the instability of the enzyme itself, using this method to test AF may bring false positive and negative results, and more AF rapid test boxes have been developed to determine the most toxic The species are mainly used by the food and feed industry to define the problem of excessive AF in food or feed. The detection accuracy of enzyme-linked immunosorbent assay needs to be improved. ^[3]

The biggest advantage of brominated fluorescence spectrophotometry is that it does not use AF reference substance for detection, and it is fast and sensitive. It is suitable for large-scale sample census and the price of the instrument is relatively low. As a result, it was found that the SFB method may produce many false positive results in the determination of traditional Chinese medicine. ^[3]

AF Removal measures of aflatoxin AF

Aflatoxin Mill Scrub

Aflatoxin is extremely unevenly distributed in food. Moldy, broken, long buds, wrinkled skin, and discolored peanut kernels are the most concentrated in peanut samples. As long as they are removed, the toxin content will be greatly reduced, or even low poison. Milling can remove most of the aflatoxin concentrated in the rice bran layer and the husk and germ layer; rubbing can remove a lot of toxins on the grain surface. ^[3]

Aflatoxin adsorption

Commonly used adsorbents are zeolite, activated white clay, activated carbon, etc. Vegetable oil containing AF can be added with adsorbents such as activated white clay or activated carbon, and toxins can be adsorbed and detoxified. For example, when Guangxi uses this method to treat peanut oil and add 1.5% white clay, the AF in peanut oil can be reduced from the original 100 g / kg. To 10 g / kg. When selecting a toxin adsorbent, it should be noted that on the one hand, the adsorption capacity must have dual data of laboratory and animal tests to prove its effectiveness; on the other hand, it is considered that the adsorbent has a high adsorption capacity, selective adsorption, broad spectrum adsorption, and no side effects. ^[3]

Aflatoxin radiation treatment

AF is unstable under UV light irradiation and can be detoxified by UV light irradiation. This method has a better effect on liquid foods such as vegetable oils, but not on solid foods. In the application of radiation method, attention must be paid to the dose and time of exposure, so as not to affect the sensory and physical and chemical properties of food. ^[3]

Aflatoxin alkali treatment

Alkali refining is a method of refining fats and oils. Adding 1% NaOH solution to fats and oils, the AF lactone ring can be destroyed to form coumarin sodium salt. The latter is soluble in water, so toxins can be removed by adding alkali and then washing with water. Adding alkaline washing can reduce the AF in the oil below the standard, and it can not even be detected. ^[3]

Aflatoxin Organic Solvent Extraction

AF is a fat-soluble toxin that is easily soluble in organic solvents. It can be extracted, separated, and detoxified with hydrated ethanol, isopropanol, acetone, n-hexane, and water. The extraction needs to be repeated 3 to 5 times, and the detoxification effect can reach more than 90%. Among them, acetone and water (90: 100) are the best. After processing the grain and oil products, the solvent must be thoroughly dried before consumption. ^[3]

Aflatoxin oxidative degradation

Bleaching powder, chlorine, hydrogen peroxide, ozone and other oxidants can quickly oxidize and remove AF. Among them, bleaching powder has the strongest detoxification effect. Highly contaminated peanut flour can be detoxified by treating it with 5% bleach for a few seconds. Grain treated with oxidants has been proved to be non-toxic by turkey feeding tests. ^[3]

Aflatoxin Chlorine Dioxide Method

The mildew-infected corn with AFB1 can effectively relieve the toxicity of AFB1 by soaking it with 250 g / mL of low concentration of chlorine dioxide for 30 to 60 minutes. ^[3]

Aflatoxin Chinese herbal medicine detoxification method

In 1976, it was discovered for the first time in China that the volatile oil in C. sibiricum could completely remove AF from food. Some components in volatile oils can undergo addition and condensation reactions with AF, change the molecular structure of toxins, and achieve the purpose of detoxification. Corn, rice, or peanuts whose AF exceeds 20 times of the national standard can be detoxified in one fell swoop by treatment with a large amount of argan oil. This method is simple and easy to implement, especially suitable for home applications, and has no impact on food quality and nutritional content. In addition, licorice, fenugreek, lupine, fennel, allspice, garlic, etc. can also remove AF. ^[3]

Aflatoxin Biological Methods

Lactic acid bacteria adhesion method is to remove AF through the self-adhesion of lactic acid bacteria and the bacteriostatic effect of the secreted metabolites. The nisin produced by lactic acid bacteria has the effects of adhering and degrading AF. ^[3]

Lactic acid bacteria are widely used in the food fermentation industry and have the effects of improving intestinal micro-ecology, antiseptic and therapeutic effects. Lactic acid bacteria can secrete many antibacterial substances and prevent the growth of pathogenic bacteria. Other microorganisms such as Bacillus subtilis, lactic acid bacteria, acetic acid bacteria and the like have the strongest ability to degrade AF. After 60 hours in liquid culture medium, 89%, 88%, and 81% can be removed, respectively. ^[3]

Aflatoxin enzymatic hydrolysis

Enzyme degradation and detoxification mainly utilize the specificity of enzymes to efficiently catalyze and degrade AF into non-toxic compounds or small molecule non-toxic substances. Enzymatic degradation has good effect in removing aflatoxin, and has strong practicability. It is suitable for various forms of contaminated food and will definitely become a hot spot for future research and applications. ^[3]

Aflatoxin growth conditions

The most basic condition for the production of aflatoxin is the presence of toxin-producing fungi. After a large number of experiments, it has been proved that the fungi that can produce AF are mainly Aspergillus flavus and Aspergillus parasiticus. Aspergillus flavus is a relatively common saprophyte that is widely distributed in various regions of the world. The suitable conditions are the breeding grounds for toxins. There are many factors that affect the growth and reproduction of Aspergillus and the production of toxins. The main factors closely related to food are moisture, temperature, food substrate, and ventilation conditions. ^[2]

Aflatoxin moisture

Water is indispensable for the survival of microorganisms. Water in food exists in two states: bound water and free water. The bound water exists in the tissue of the food itself. It is a part of living tissue and is necessary for all physiological processes of cells. The water available to microorganisms is free water. Generally speaking, the moisture content of rice and wheat is below 14%, soy is below 11%, dried vegetables and dried fruits are below 30%, the growth of microorganisms is difficult, and the part of water that can be used by microorganisms is called water activity Water activity (abbreviation Aw). The Aw of pure water is 1.0 (equivalent to 100% relative humidity). When the Aw value is smaller, the bacteria can use less water, and the closer the water activity is to 1, the easier it is for microorganisms to grow and reproduce. When Aw in food is 0.98, microorganisms are most likely to grow and reproduce. When Aw is reduced to 0.93, microbial reproduction is inhibited, but mold can still grow. When Aw is less than 0.7, mold growth is inhibited to a certain extent, which can prevent toxin production. Mold growth. ^[2]

Aflatoxin temperature and ventilation

Temperature has an important effect on the reproduction and toxicity of molds. The optimal temperature for different types of molds is different. At a relative humidity of 80% to 90%, the most suitable temperature for most molds to breed is 25 to 30 ° C. Toxicity cannot be produced below 0 ° C. For example, the lowest breeding temperature range of Aspergillus flavus is 6 to 8 ° C, the highest breeding temperature is 44 to 46 ° C, the most suitable growth temperature is about 37 ° C, and the poisoning temperature is slightly lower than the optimal growth temperature, which is 25 to 32 ° C. Slow ventilating is more prone to produce toxins than fast air-drying molds. ^[2]

Aflatoxin Food Matrix

As with other microorganisms, the saprophytic substrate is important. Different food matrices have different growth conditions. Generally speaking, nutrient-rich foods have a high possibility of mold growth. Natural matrices produce better toxins than artificial culture substrates. ^[2]

Aflatoxin biological control agent

Many bacteria and fungi, such as lactic acid bacteria, Bacillus, Xanthomonas, yeast, etc., have the ability to inhibit the growth and production of Aspergillus flavus. ^[7]

Aflatoxin lactic acid bacteria

Studies have shown that many strains of the genus Lactobacillus, including Lactobacillus, Bifi-dobacterium, Propionibacteri-um, and Lactococcus, have been reported to adsorb aflatoxins. Although lactic acid bacteria can adsorb aflatoxin, this adsorption may be reversible and easily cause toxin residues. Furthermore, lactic acid bacteria are anaerobic bacteria, and it is difficult to ensure an anaerobic environment in practical applications, which limits lactic acid bacteria as antagonistic bacteria Practical application. ^[7]

Aflatoxin bacillus

The bacteriostatic substance produced by Bacillus subtilis has good heat resistance. If the active substance secreted by it can be purified and identified, and its active substance is used for the control of aflatoxin pollution, it will bring to the production of crops. Great benefits. ^[7]

Aflatoxin Xanthomonas

Xanthomonas oryzae is a type of biocontrol bacteria that has been studied earlier. As early as the 1960s and 1970s, some scholars found that cell cultures of Xanthomonas can remove aflatoxin B1 in aqueous solutions; its dead cells remove yellow The ability of Aflatoxin B1 is affected by temperature and pH. Aflatoxin B1 adsorbed by living cells cannot be extracted by the liquid phase. In addition, cell-free extracts of Rhododococcus erythropolis and Mycobacterium fluoranthenivorans can significantly reduce aflatoxin B1 in food and feed. Myxococcus fulvus is an aerobic gram-negative coryneform bacterium that is widely found in soil. The extracellular products they secrete can break down different biological macromolecules and entire microorganisms. ^[7]

Aspergillus aflatoxin and Aspergillus parasiticus

The use of non-toxic aflatoxins and aspergillus parasiticus can effectively control aflatoxins before harvest and have been applied. As early as 1992, some scholars have proposed that spreading non-toxic parasitic Aspergillus strains on the soil where peanuts grow can reduce the aflatoxin content of peanuts by 83% to 85%. Similarly, the introduction of non-toxic aflatoxin strains into the soil can also reduce the aflatoxin content in cotton seeds. In recent years, the American Environmental Protection Association has also registered two non-toxic aflatoxin strains to prevent cotton and peanut aflatoxin contamination, and has been widely tested in test fields in many states in the United States. In Africa, Australia, and China, non-toxic Aspergillus flavus strains that can effectively inhibit the production of aflatoxin have also been screened. These strains can reduce the number of field-producing strains by more than 95%. ^[7]

The introduction of Aspergillus flavus and Aspergillus parasiticus to control the microbial flora in the soil, which preferentially replaces the original toxin-producing strains in the soil during the growth of the crop, is effective in reducing the aflatoxin contamination before harvest. Earlier field trials directly soaked spore suspensions and seeds of non-toxic strains or seeded the spore suspensions directly into the soil, although the effect was very obvious, but the cost was higher; in recent years, the solid-state fermentation method was used Incubate the spores. After incubation, dry at 50 ° C and store at 5 ° C until use. Soil temperature is one of the important factors affecting the biological control of aflatoxin contamination. In the laboratory, the temperature of germination of aflatoxin spores must be higher than 10 ; but in the test field, the spores will germinate when the temperature is higher than 20 . Therefore, it is necessary to wait until the soil temperature is higher than 20 ° C to apply the non-toxic strains to the test field. Different regions should determine the application date according to specific conditions. ^[7]

Although many non-toxic Aspergillus flavus and Aspergillus parasiticus strains have been successfully applied in the field to control aflatoxin contamination, the method of direct inoculation of spores will change the microbial flora in the field and even affect the growth of normal flora. This is bound to Yield. In addition, this method can only be applied when the soil temperature is higher than 20 ° C, and its application is limited in areas where crops are grown in multiple seasons. ^[7]

Aflatoxin yeast

Experiments have shown that saprophytic yeasts, such as Candida and Pichia, can significantly inhibit the growth of Aspergillus flavus, but whether it can be effectively used in the field remains to be further studied. . ^[7]

Aflatoxin edible fungi

Some scholars have co-cultured Pleurotus ostreatus and Aspergillus flavus, and the results show that Pleurotus ostreatus can inhibit the growth of Aspergillus flavus; after 3 weeks of infection with Aspergillus flavus in straw and corn cob, inoculation with Pleurotus ostreatus can make the straw and corn cob yellow Aflatoxin content is reduced. Pleurotus ostreatus can produce an extracellular enzyme with a molecular weight of 90kD, and it has been proved that the enzyme can effectively degrade AFB1 by thin-layer chromatography. Fluorescence measurement shows that the enzyme can catalyze the opening of the lactone ring of AFB1, thereby achieving the effect of degrading toxins. ^[7]

Aflatoxin detoxification enzyme is a substance that has high efficiency in degrading aflatoxins so far. It is an enzyme extracted from edible fungi and has high safety. However, the yield of this enzyme needs to be further improved and is widely used in production. There is still some distance. ^[7]

Aflatoxin other fungi

It has been reported that Trichoderm viride, Mucor ambiguus, and a few other fungi also have a good ability to degrade AFB1. However, some of these strains may produce AFB under conditions that change. Studies have shown that when Aspergillus niger and its mutant strains are mixed with Aspergillus flavus to produce a cricket culture, although the wild type has only a slight inhibition on the growth of Aspergillus flavus, it can reduce the ability of Aspergillus flavus to produce toxins and synthesize pigments; and The mutant strain has a strong ability to inhibit the growth of Aspergillus flavus. ^[7]

Aflatoxin medicinal plant extract

Medicinal plants contain many effective bacteriostatic ingredients. A large number of studies have shown that intercropping of medicinal plants and crops can effectively inhibit the growth of Aspergillus flavus and reduce the probability of crops being contaminated by aflatoxins. ^[7]

Some scholars have isolated the antibacterial substance lignan from the medicinal plant Larrea tridentata, which can significantly inhibit the growth of Aspergillus flavus. In addition, medicinal plants such as Sida acuta, Senna Alata, Cinnamomum cassia, lemon, Mosla chinensis, Carya cathayensis and Eucommia ulmoides Aspergillus flavus spore germination and mycelial growth were inhibited. Most of the above-mentioned medicinal plants are woody plants, except for the genus Schizandra. Although they have a wide application prospect in clinical treatment, it is difficult to promote the biological control of field crops. ^[7]