**3. AFB1 toxification and toxic mechanisms**

#### **3.1 The effects of AFB1 on the food chain**

*Aflatoxin B1 Occurrence, Detection and Toxicological Effects*

Toxic fungi often live in the human crops and produce mycotoxins such as aflatoxins. Toxic fungi in crops can be divided into two categories according to whether their mycotoxins are produced before or after crop harvest. The first category is termed as field fungi, which often invade crops and produce mycotoxins before harvest. The another, also called storage fungi, mostly occurs in the storage of crops after harvest. The sources of both types of toxigenic fungi are affected by environmental factors. Crops before harvest, fungi can invade crops to produce toxins by interacting with other organisms, such as insects. The harvested crops are regulated by factors such as nutrients, temperature and humidity in the air, and biological agents (insects, competitive interference). Furthermore, toxigenic fungi can be divided into four types according to their effects on crops: *A. fungi* acting as plant pathogens, such as grass fungi; *b.* fungi producing fungal toxin and stressing plants, such as *Candida* and *A. flavus*; *c.* fungi acting as colonizers (such as *Aspergillus flavus*), which first colonize in harvest plants and subsequently, produce mycotoxin and contaminate crops; and *d.* fungi decomposing plants (such as *Penicillium chrysogenum* and *Aspergillus* 

The crop fungi inoculate the growing crop kernels in the field and proliferate in storage under suitable conditions. Among known crop fungi, *Aspergillus*, *Fusarium*, and *Penicillium* have identified as toxin-producing fungi. Although many compounds produced by these toxin-producing fungi are known as their toxins, there have been only five important agricultural mycotoxins until now: deoxycinol, praurone, ochratoxin A, fumarin and aflatoxin. Mycotoxins produced by *Fusarium* include fumonisins, deoxycinol and zerneone. Although *Penicillium* and *Aspergillus* are storage fungi, they can also invade field stress plants and produce toxins. Increasing evidence has shown that *Penicillium* can produce ochratomycin, citrinin and patron, and that *Aspergillus* can produce aflatoxin,

Several previous reviews have fully summarized the occurrence and biosynthesis of AFB1. Briefly, AFB1 are an important class of mycotoxins mainly produced by *Aspergillus flavus* and *Aspergillus parasiticus*. This term is so named and concerned because of the following several reasons: *a.* this mycotoxin has been identified in the *A. flavus* and regarded as pathologic agent of "turkey X" disease; *b.* this mycotoxin is the first B-type aflatoxin which can produce fluorescent characteristic under UV light; and *c.* AFB1 often display its severe toxic effects on human and animals. Usually, it is synthesized through 18 biological steps under the regulations of a huge neighbor gene cluster consisting of about 60–70 kb in original fungi. This biosynthesis at least involves in the three stages, consisting of the formation of primary product hydroxyversicolorone (the first to eighth step), middle product versicolorin B (the ninth to twelfth step) and ultimate product AFB1 (the thirteenth to eighteenth step). During the biosynthesis of AFB1, several key enzymes, including nicotinamide-adenine dinucleotide, nicotinamide-adenine dinucleotide phosphate reduced form, and 2S-adenosylmethionine, are required

**2.1 Toxic fungi and their classifications**

*oryzae*), which often live in the soil [6, 7].

for the biosynthesis limitation [3, 10, 11].

citrinin and baturin [8, 9].

**2.2 AFB1 occurrence**

**2. AFB1 occurrence**

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*A. flavus* is widely present in the soil, causing pollution to many crops such as corn, peanuts, rice, etc., and using these crops as a host produces aflatoxin, which in turn contaminates crop fruits. Aflatoxin contamination of food and animal feed has now become a major problem that threatens food safety. Crops can be contaminated with fungi in the field, harvested, and stored, making crop contamination control difficult. The Food and Agriculture Organization of the United Nations (FAO) estimates that 25% of the world's food crops are contaminated with mycotoxins [12]. Aflatoxins, the most harmful toxins, are the most difficult to deal with because they are commonly found in corn, peanuts and their products, cottonseed, peppers, peppers, pistachios and other foods. Studies have shown that the type of mold and its concentration of conidia, as well as the moisture content of corn, play a key role in the process of mold infection, spoilage and AFB1 production in corn. In the field, Aspergillus flavus enters the plant primarily by vaccination or secondary inoculation, which in turn infects the seed to produce aflatoxin. In spring, the source of inoculation of Aspergillus flavus spores is mainly from the propagules in the soil, the plant debris in the soil, and the wintering mycelium, insects or the Aspergillus flavus nucleus in the soil in the litter. In corn fields, spores are mainly derived from the spore-derived sclerotium conidia of Aspergillus flavus. Before the harvest, the insects damage the corn kernels to form the sclerotia. When harvesting, the sclerotia is dispersed in the soil, and the spring conidia are exposed on the surface of the sclerotium. A secondary inoculation source was found in the cotton field, and *A. flavus* was isolated from the leaves, flower buds and leaf discs of cotton, the content was 15, 94, or 56%, respectively. Most of the colonies were mainly distributed on the calyx tablets. Conidia are the main source of secondary inoculation. Fungal spoilage and mycotoxin contamination are major problems in crop contamination. Grains are affected by storage conditions and the environment after harvesting, such as storage containers, oxygen content in the air, water activity, temperature, and insects, all of which are factors of toxin contamination [7]. If stored poorly, it will increase the contamination of mycotoxins. As one of the main crops for human food and livestock feed, corn is planted annually at 120 million hectares and is one of the most polluted toxins. Aspergillus flavus is the main fungus that is infected after corn harvest. The drying and storage conditions of corn before storage are extremely important. Moisture can accumulate from the activity of pests, which provides ideal conditions for the proliferation of fungi and the accumulation of mycotoxins. In order to reduce the effects of mycotoxins on food and feed chains, it is necessary to control pest and fungal contamination [13, 14]. Humidity and temperature have important effects on mold growth and mycotoxin production. Therefore, humid and hot climates in tropical and subtropical regions provide favorable conditions for mold growth. The moisture content of the grain is generally expressed in terms of water content. Pathogenic fungi that invade crops prior to harvest typically require higher moisture levels (200–250 g/kg) to infect, while fungi that can proliferate during storage (130–180 g/kg) require higher moisture levels. Therefore, most feeds with a water content above 130 g/kg are prone to mold growth and formation of mycotoxins [15]. Therefore, the control of the moisture content in the grain becomes particularly important, especially in the control of moisture at the harvesting point, while the drying and storage of the grain before storage and the frequency of grain drying and plowing, as well as

the insects and microorganisms in the stored grain are also Factors affecting water activity. It was found to be closely related to climate in the detection of aflatoxin levels after storage of Benin corn. Benin's aflatoxin contamination levels increase in dry and hot conditions in June each year; while the harvest season is affected by climate, the peaks of rainfall or the late planting of corn will increase aflatoxin levels during the rainy season [16]. Limiting the occurrence of AFB1 before crop harvesting can be achieved by reducing drought and temperature, controlling weeds, reducing insect damage, efficient harvesting techniques, and reducing soil Aspergillus spores through crop turnover. Using biological control, a competitive, non-toxigenic strain of Aspergillus flavus is applied to the developing soil to compete with naturally occurring toxigenic strains. Studies have shown that these biological control strategy can aflatoxin. The pollution is reduced by about 80–90%. Control of afb1 sensitive crops after harvest can be achieved by controlling factors that affect fungal growth, such as water activity, temperature, gaseous environment, and the use of pesticides or food preservatives. Harvesting only cereals with a moisture content of around 24% reduces the risk of grain damage and subsequent AFB1 production [17, 18].

### **3.2 The toxic effects of AFB1 on human and animals**

In 1963, Asao et al. completed the structural clarification of AFB1, a member of the aflatoxin family containing a fused difuranyl group [19]. AFB1 is highly toxic to humans and several animals, and has three major characteristics: organophilic, genotoxic, and carcinogenic. Its pro-organism is mainly caused by damage to the liver, which can lead to hepatic hemorrhage and hepatocyte necrosis. The genotoxicity is mainly to induce the formation of AFB1-DNA adduct and the hot spot mutation of P53 gene. The carcinogenicity is mainly caused by hepatocellular carcinoma. The main toxicological effect of AFB1 is to induce DNA damage. AFB1 has been proven to be the main cause of liver cancer in patients with hepatitis B virus infection. It is a genotoxic liver cancer, which may cause cancer by inducing DNA adducts, leading to genetic changes in target cells, leading to DNA strand breaks and DNA base damage. And oxidative damage can eventually lead to cancer. AFB1 is mainly metabolized by the liver, and AFB1 taken from food is mainly metabolized by the cytochrome P450 enzyme to the final carcinogen AFB1-8-9 epoxide (AFBO). When AFBO reacts with DNA, it inhibits gene mutation in P53, a hotspot coding region of exon 249, by interacting with guanine bases, which may lead to HCC. AFB1 is metabolized by the P450 system into a number of hydroxylated products, including AFM1, AFQ1, AFP1, AFB2a [11, 20–25]. After aflatoxin is ingested into the human body, it mainly manifests as an acute or chronic disease. Acute attacks usually involve high concentrations of aflatoxins. For example, 317 cases of acute liver failure occurred in Kenya in 2004. The main reason is the consumption of aflatoxin-contaminated corn, and the case of patients with AFB1 lysine in serum. The adduct concentration was the highest in history. Growth retardation, immunosuppression, and carcinogenicity are chronic effects, and the incidence of chronic attacks in developing countries is higher because of exposure to low levels of aflatoxin intake [26].

#### *3.2.1 Effect of aflatoxin on growth and development*

An epidemiological survey was conducted in West Africa to measure exposure to aflatoxins in children between 9 months and 5 years of age, and their growth, development and height were examined against the reference population of World Health Organization (WHO) [27]. Studies have shown a strong association between

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*The Toxification and Detoxification Mechanisms of Aflatoxin B1 in Human: An Update*

exposure to aflatoxin in children and dysplasia and underweight. In a field outbreak of aflatoxin, egg production fell by 5% [28]. The study data showed that for every 1 mg/kg of aflatoxin AFB1 in the feed, the growth rate of pigs would be reduced by

In these animal studies, AFB1 has been shown to induce immunosuppression. For example, in studies of AFB1 exposed animals, it was found that the activity of B cells and T cells decreased, because T cells were more sensitive to AFB1 toxicity [30]. Research data from GY et al. showed that chicken phagocytic cells were severely damaged during aflatoxosis, and the ability to remove foreign substances from the circulation decreased, which may reduce the ability to process antigenic components. Aflatoxell chickens are more susceptible to infection [31]. In pigs, AFB1 exposure reduces lymphocyte response to mitogens, inhibits large phage migration and delayed skin allergic reactions [32]. Although many data on AFB1 immune effects have been obtained from animal studies, there is little data on the effects of long-term consumption of food contaminated with AFB1 on the human immune system. The effect on the immune system by aflatoxins in the diet of Gambian children found a decrease in sIgA levels in saliva, probably due to the high level of exposure to aflatoxins in the diet [33]. In a study of aflatoxin AFB1 exposure and cellular immune status in 64 Ghanaians, it was found that AFB1 exposure may result in a decrease in the major constituent cell T cells and B cells that cause lymphocyte subpopulations. High levels of AFB1 albumin adducts significantly reduced perforin- and granzyme a levels in CD8+ cytotoxic T cells compared to low levels of AFB1 albumin adduct. In participants with high levels of AFB1, changes in these immune parameters may result in impaired cellular immune function, thereby

Since the contamination of aflatoxins in food poses a risk to human health and leads to serious economic losses in crops, we have every reason to implement new methods to ensure the safety of food production. There are two main methods of implementation: (a) prevention of mold contamination and growth; (b) detoxification of contaminated products by opponents. Prevention of mycotoxin contamination can be achieved by storage before or after harvesting of the crop. However, the pollution of toxins is inevitable, and the detoxification pathway for contaminated food after harvest has been the subject of our in-depth research. Detoxification methods commonly used are physical methods and chemical methods. This article will focus on new research on detoxification of harvested contaminated crops.

The most common way to remove AFB1 using physical methods is to heat and use gamma rays. Aflatoxins are highly thermostable. Studies have shown that AFB1 levels are significantly reduced by heating at 100 and 150°C for 90 minutes, respectively, at 41.9 and 81.2%. The AFB reduction rate of the soy milk after cooking was 97.9%, and the AFB1 reduction rate of the steamed soybeans after cooking was 33.6%. And studies have shown that high pressure cooking is better than ordinary cooking to remove AFB1. When the soybean is steamed or steamed in a pressure cooker, the reduction rate of the pressure cooker is about 10% higher than that

*DOI: http://dx.doi.org/10.5772/intechopen.89221*

reducing host resistance to infection [34].

**4. Detoxification of AFB1**

**4.1 Physical method**

16% and broilers by 5% [29].

*3.2.2 Immunosuppressive*

exposure to aflatoxin in children and dysplasia and underweight. In a field outbreak of aflatoxin, egg production fell by 5% [28]. The study data showed that for every 1 mg/kg of aflatoxin AFB1 in the feed, the growth rate of pigs would be reduced by 16% and broilers by 5% [29].
