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Aflatoxins are notorious mycotoxins often associated with moldy food. Their significance was highlighted in 1960 when a large number of turkeys in the UK suddenly died after being fed peanut meal contaminated by fungi. Not all food or feed contaminated by fungi contains residual aflatoxins. Aflatoxins are primarily secondary metabolites produced by two fungi belonging to the Aspergillus genus: A. flavus and A. parasiticus. Another important class of fungal secondary metabolites is penicillins, produced by Penicillium. Currently, four types of aflatoxins are known: B1, B2, G1, and G2 (Figure 1). These are low-molecular-weight compounds with strong toxicity and carcinogenicity (Table 1). Among these, aflatoxin B1 is the most toxic, often causing liver damage in animals and humans, making it a serious concern.
However, are aflatoxins only found in moldy peanuts and their products? Actually, no. Researchers later discovered aflatoxins in dairy products, particularly the fifth type, aflatoxin M1. Dairy farmers supplement cattle feed with formulated feed to promote growth and increase milk production. If improperly handled, this feed can become contaminated with aflatoxins. When cows consume such contaminated feed, about 1-2% of the aflatoxin B1 is metabolized and converted into aflatoxin M1, which is then excreted in milk. Although aflatoxin M1 is less toxic than B1, long-term consumption of dairy products with excessive M1 can still cause liver damage.
According to food hygiene standards set by the Department of Health, aflatoxin levels in peanuts and their products must not exceed 15 ppb. Ingesting large amounts of aflatoxin-contaminated food can lead to acute hepatotoxicity or even death. Main symptoms include vomiting, abdominal pain, pulmonary edema, convulsions, coma, or liver, kidney, or heart failure, as well as cerebral edema leading to death. Epidemiological studies indicate that regions with severe aflatoxin contamination often have higher rates of liver cancer. Aflatoxins may also be a contributing factor to liver cancer in hepatitis B virus carriers.
The synthesis pathway of aflatoxins is generally believed to originate from primary metabolites. When fungal growth begins, primary metabolism starts, during which little to no aflatoxin is produced. As nutrients such as phosphorus, nitrogen, or other trace elements required for primary metabolism become depleted, growth slows, and primary metabolism is disrupted. The accumulation of various primary metabolites triggers or enhances the activity of enzymes needed for secondary metabolism, leading to the production of secondary metabolites. For example, in A. flavus and A. parasiticus, the polyketide biosynthesis pathway surpasses fatty acid biosynthesis, thereby promoting aflatoxin synthesis.
The latest method for detecting aflatoxins utilizes monoclonal antibodies. These antibodies are characterized by their high affinity for aflatoxins B1, B2, G1, and G2, enabling the detection of total aflatoxin content in samples without cross-reactivity to aflatoxin derivatives.There are many factors that influence the production of aflatoxins, including temperature, humidity, substrate, cultivation time, and the significant variation in aflatoxin production among strains from different regions. A report by Sorensen et al. in 1967 indicated that *A. flavus* and *A. parasiticus* can produce aflatoxins at temperatures ranging from 11 to 37°C. Diener and Davis (1967) studied the effect of relative humidity on aflatoxin accumulation in stored peanuts and found that damaged peanuts produced small amounts of aflatoxins at a relative humidity of 85%, whereas intact peanuts required a relative humidity of 87–89% for aflatoxin production. At a relative humidity of 97–99%, aflatoxins were produced within a temperature range of 13–41.5°C. Ehrlich and Cotty (2002) noted that different strains of the same species from various regions produced vastly different amounts of aflatoxins, a phenomenon attributed to differences in regulatory gene levels. They observed that when *A. flavus* strains from Arizona, USA (SB), and Benin, West Africa (SBG), were cultured in the lab, the SBG strain produced significantly less aflatoxin when nitrate was used as the nitrogen source compared to ammonium salts. Further research concluded that aflatoxin production is regulated by the genes *AflR* and *AflJ*, which are in turn controlled by *AreA*-binding sites. Additionally, the number of *AreA*-binding sites also regulates aflatoxin production. The *A. flavus* strains from these two regions differed in their *AreA*-binding site content, with SB having more and SBG having fewer, corresponding to higher and lower aflatoxin production, respectively.
Fungi that produce aflatoxins are not only found in peanuts but also in crops such as corn, wheat, oats, cottonseed, and pigeon peas. Commercially available agricultural products are often contaminated with *Aspergillus* and aflatoxins due to environmental conditions, hygiene factors, and storage duration. Aflatoxins exhibit high thermal stability, making them resistant to destruction or removal by conventional processing methods. Animal studies have shown that even extremely low doses of aflatoxins can cause cancer, making the prevention of fungal contamination in agricultural products a critical issue in the agricultural sector.
To minimize the risk of aflatoxin exposure in daily life, it is advisable to purchase fresh, well-packaged products and check for signs of mold by examining their appearance and color. Store these products in a dry, cool, and well-ventilated place, and discard them if they exceed their expiration date. Limit consumption of peanut-based products such as peanut butter and peanut flour. Since poultry are highly susceptible to aflatoxin ingestion, it is also recommended to reduce intake of animal offal, especially liver. Moldy food should be discarded immediately to avoid aflatoxin exposure.
Table 1. Toxicity and Carcinogenicity of Aflatoxins
References:
1. Ehrlich, K. C. and P. J. Cotty. 2002. Variability in nitrogen regulation of aflatoxin production by Aspergillus flavus strains. Appl. Microbiol. Biotechnol. 60:174-178.
Marth, E. H. 1982. Aflatoxin (part of chapter 4). In G. Reed (ed.), Prescott & Dunn’s Industrial Microbiology, 4th ed.
Source: http://vschool. scu. edu. tw/ biology/ content/ mbiology/ mb030. htm
How Much Do You Know about Aflatoxin?
However, are aflatoxins only found in moldy peanuts and their products? Actually, no. Researchers later discovered aflatoxins in dairy products, particularly the fifth type, aflatoxin M1. Dairy farmers supplement cattle feed with formulated feed to promote growth and increase milk production. If improperly handled, this feed can become contaminated with aflatoxins. When cows consume such contaminated feed, about 1-2% of the aflatoxin B1 is metabolized and converted into aflatoxin M1, which is then excreted in milk. Although aflatoxin M1 is less toxic than B1, long-term consumption of dairy products with excessive M1 can still cause liver damage.
According to food hygiene standards set by the Department of Health, aflatoxin levels in peanuts and their products must not exceed 15 ppb. Ingesting large amounts of aflatoxin-contaminated food can lead to acute hepatotoxicity or even death. Main symptoms include vomiting, abdominal pain, pulmonary edema, convulsions, coma, or liver, kidney, or heart failure, as well as cerebral edema leading to death. Epidemiological studies indicate that regions with severe aflatoxin contamination often have higher rates of liver cancer. Aflatoxins may also be a contributing factor to liver cancer in hepatitis B virus carriers.
The synthesis pathway of aflatoxins is generally believed to originate from primary metabolites. When fungal growth begins, primary metabolism starts, during which little to no aflatoxin is produced. As nutrients such as phosphorus, nitrogen, or other trace elements required for primary metabolism become depleted, growth slows, and primary metabolism is disrupted. The accumulation of various primary metabolites triggers or enhances the activity of enzymes needed for secondary metabolism, leading to the production of secondary metabolites. For example, in A. flavus and A. parasiticus, the polyketide biosynthesis pathway surpasses fatty acid biosynthesis, thereby promoting aflatoxin synthesis.
The latest method for detecting aflatoxins utilizes monoclonal antibodies. These antibodies are characterized by their high affinity for aflatoxins B1, B2, G1, and G2, enabling the detection of total aflatoxin content in samples without cross-reactivity to aflatoxin derivatives.There are many factors that influence the production of aflatoxins, including temperature, humidity, substrate, cultivation time, and the significant variation in aflatoxin production among strains from different regions. A report by Sorensen et al. in 1967 indicated that *A. flavus* and *A. parasiticus* can produce aflatoxins at temperatures ranging from 11 to 37°C. Diener and Davis (1967) studied the effect of relative humidity on aflatoxin accumulation in stored peanuts and found that damaged peanuts produced small amounts of aflatoxins at a relative humidity of 85%, whereas intact peanuts required a relative humidity of 87–89% for aflatoxin production. At a relative humidity of 97–99%, aflatoxins were produced within a temperature range of 13–41.5°C. Ehrlich and Cotty (2002) noted that different strains of the same species from various regions produced vastly different amounts of aflatoxins, a phenomenon attributed to differences in regulatory gene levels. They observed that when *A. flavus* strains from Arizona, USA (SB), and Benin, West Africa (SBG), were cultured in the lab, the SBG strain produced significantly less aflatoxin when nitrate was used as the nitrogen source compared to ammonium salts. Further research concluded that aflatoxin production is regulated by the genes *AflR* and *AflJ*, which are in turn controlled by *AreA*-binding sites. Additionally, the number of *AreA*-binding sites also regulates aflatoxin production. The *A. flavus* strains from these two regions differed in their *AreA*-binding site content, with SB having more and SBG having fewer, corresponding to higher and lower aflatoxin production, respectively.
Fungi that produce aflatoxins are not only found in peanuts but also in crops such as corn, wheat, oats, cottonseed, and pigeon peas. Commercially available agricultural products are often contaminated with *Aspergillus* and aflatoxins due to environmental conditions, hygiene factors, and storage duration. Aflatoxins exhibit high thermal stability, making them resistant to destruction or removal by conventional processing methods. Animal studies have shown that even extremely low doses of aflatoxins can cause cancer, making the prevention of fungal contamination in agricultural products a critical issue in the agricultural sector.
To minimize the risk of aflatoxin exposure in daily life, it is advisable to purchase fresh, well-packaged products and check for signs of mold by examining their appearance and color. Store these products in a dry, cool, and well-ventilated place, and discard them if they exceed their expiration date. Limit consumption of peanut-based products such as peanut butter and peanut flour. Since poultry are highly susceptible to aflatoxin ingestion, it is also recommended to reduce intake of animal offal, especially liver. Moldy food should be discarded immediately to avoid aflatoxin exposure.
Table 1. Toxicity and Carcinogenicity of Aflatoxins
| Types of Aflatoxin | Toxicity （LD50 mg/kg） | Relative Carcinogenicity |
| B1 | 0.36 | 100 |
| M1 | Approx. 0.36 | 3 |
| G1 | 0.78 | 3 |
| B2 | 1.69 | 0.2 |
| G2 | 2.45 | 0.1 |
References:
1. Ehrlich, K. C. and P. J. Cotty. 2002. Variability in nitrogen regulation of aflatoxin production by Aspergillus flavus strains. Appl. Microbiol. Biotechnol. 60:174-178.
Marth, E. H. 1982. Aflatoxin (part of chapter 4). In G. Reed (ed.), Prescott & Dunn’s Industrial Microbiology, 4th ed.
Source: http://vschool. scu. edu. tw/ biology/ content/ mbiology/ mb030. htm
2009/12/04 23:52