Aflatoxin is a heterocyclic compound produced by Aspergillus flavus and Aspergillus parasiticus, and it’s metabolites are mainly in the types of B1, B2, G1, G2, M1, and M2.
Aspergillus flavus in culture medium
Aflatoxins are very heat-resistant and can only be largely deactivated by prolonged high temperature (100-120°C), such as autoclaving and calcination. In general, the heat of pasteurization or baking bread (the highest temperature in the center is 100°C) is not enough to completely inactivate aflatoxins. These toxins are sensitive to strong acids and alkali. Therefore, the process of extracting free fatty acids with sodium hydroxide can further destroy the activity of the toxin.
Although aflatoxins are highly toxic, it is necessary to take a single dose of moldy food containing a large amount of aflatoxin to cause acute poisoning. Chronic poisoning in humans is the result of persistent sub-acute intake of aflatoxin, and cirrhosis and liver fibrosis are common in chronic poisoning. Moldy foods or foods and peanuts contaminated with dust and mildew during transportation may also contain aflatoxin and cause harm to humans. If toxins accumulate in the liver, heart muscle and other muscle will enhance its toxicity. Direct damage to the liver can lead to genetic aberrations (terrestrial or stillbirth), and a large number of animal test results (rats, birds, and fish) show that they have strong carcinogenicity, mainly inducing liver cancer. Some people think that it will induce kidney cancer. The carcinogenicity of aflatoxins is significantly related to the effect of other carcinogens such as dimethylnitrosamine.
Sporangia of Aspergillus flavus under the microscope
In the various aflatoxins, aflatoxin B1 is the most toxic variety, and the level of toxicity is followed by M1, G1, M2, B2, and G2. Therefore, many countries have specified the limit value of aflatoxin in food. Toxin levels of Aspergillus flavus in food are not allowed to exceed this standard value.
Aspergillus flavus is dominant in mold commonly found in warm areas. Its range of growth temperature is from 4 to 50°C, and the optimum growth temperature is 25-40°C. The minimum temperature for formation of aflatoxin is 5-12°C, the optimum temperature for formation of aflatoxin is 20-30°C (28°C) and the highest temperature for formation of aflatoxin is 45°C. In meat products, when the temperature is below 10°C, no aflatoxin can be formed. Aspergillus is more drought-tolerant than other molds, and under the environment on the acidity and alkalinity have little effect on it. Aflatoxin can be produced under the acidic condition of pH 2-9, but under acidic conditions between pH 2.5-6.0, the amount of generation in toxin is the largest. Aspergillus flavus can grow in an environment with extremely low content of oxygen and ferment in an anoxic environment. Even in the cold storage filled with carbon dioxide, the growth of Aspergillus flavus is not affected, but the formation of aflatoxin can be significantly delayed.
Aspergillus flavus and Aspergillus parasiticus are widely found in soil, dust, plants, and fruits. It is especially common in tropical and subtropical stone fruits and cereals. Therefore, it is necessary to pay attention to the inspection of raw materials of food particularly susceptible to contamination in aflatoxin, and the foods processed with that raw materials in aflatoxin, including peanuts, walnuts, pistachios, almonds, peach kernels, plum kernels, shredded coconut, and sesame seeds.
Aerial hyphae and conidia of Aspergillus flavus under microscope
Where does aflatoxin come from?
He Jianguo, an associate professor at the College of Food Science and Nutritional Engineering of China Agricultural University, said that aflatoxins are a mycotoxin are metabolites. If food fails to dry in time and will produce and store molds, which are widely found in life. Due to its strong toxicity and carcinogenicity, it is strictly regulated in national food standards and feed standards. Aflatoxin M1 belongs to mycotoxin, which is a hydroxylated metabolite of aflatoxin B1 in animals. It is highly toxic and carcinogenic. It may induce liver cancer, so it was listed as a type of carcinogen by the World Health Organization Cancer Research Institute as early as 1993.
As for the reason why aflatoxin appears in dairy products, Dairy senior person Song Liang said, there are probably three reasons. One is that the cows eaten the mildewed feed causes problems in the raw milk. The second is that the machine is not clean in the process of the production process. And there is the mildew of organic matter in the machine. The third is that after the production of the product is completed, the packaging is not tight enough. After the air leak, it combines with the organic matter in the air, which may cause aflatoxin.
Find aflatoxin in milk for the first time?
According to experts, even if the consumer boils milk, it will not help to eliminate aflatoxin. There has been no large-scale effective detoxification method in milk in the industry so far. The most fundamental method is to prevent cows from eating the contaminated feed.
He Jianguo said that aflatoxin has a wide range of pollution in grain food, and according to the probability of pollution it can be divided into three categories. Peanuts, peanut products, and corn are most susceptible to pollution. The cottonseed, rice, wheat, and barley does not easily tend to contamination of aflatoxin, and soybean is most not susceptible to pollution of aflatoxin. In China, contamination of aflatoxin in the high temperature and high humidity areas along the Yangtze River and south of the Yangtze River is quite serious. Aflatoxins may also be detected in some animal foods. The main reason is that animals have eaten aflatoxin-containing feed, and their body remains aflatoxin in the form of metabolism.
Why do excessive aflatoxins still exist by passing many inspections?
In fact, since 2011 major dairy companies have increased their testing ability for aflatoxins. Their detection is not very difficult, so the companies inspect every batch of products. Since 2014, China's supervision of the domestic dairy industry can be described as the most stringent in history. For each dairy enterprise, it has been re-examined and has issued certification, so why is there a phenomenon of aflatoxin exceeding the standard?
In this regard, Cao Ming, deputy secretary-general of the Shanghai Dairy Industry Association, explained that there are two major questions need to seek answers. Firstly, does the company inspect every batch of products? Is it related to the cost of personnel and testing, management loopholes, corresponding rule without strictly complied and fluke mind? Secondly, is the enterprise's feed to the farmers managed in a unified manner?
Generally, farmers are often identified the feed by the naked eye when handling mildewed feed. The large size of molds can be identified by naked eyes, but the small size of molds is not easily recognized. This phenomenon brings an alarm to the supervisory department. In the future, more attention should be paid to the quality control of the feed and raw milk in a source, Song Liang said.
The insiders pointed out that the small pasture lacks control measures for the quality and safety of self-made feed, and in the future, it needs to adopt a more professional and systematic form for feed management. The incidence of aflatoxin exceeded the standard in the major dairy companies alarms us. The quality of dairy products is not only concerned about downstream management, but more related to the quality of raw milk and the process of dairy production in the milk enterprise, The supervision of it should be comprehensively, and take the entire industrial chain into account and ensure that dairy products do not leak from beginning to end.
To sum up, prevention and control measures for mycotoxins need to be taken. The companies need to strictly control the quality of feed and do not use feed or raw materials that are moldy, deteriorated, or too hydrated. And timely detect mycotoxins in the feed or every batch of product. The supervision should implement the standard strictly and strengthen the regulation in food safety.