**2. Aflatoxin properties**

All mycotoxins are low-molecular-weight natural products (i.e., small molecules) (Bennett, 1987 cited [3]). The hyphal structure of filamentous fungi has evolved to utilize solid substrates efficiently by growing over surfaces and penetrating into solid matrices. Moulds are able to se‐ crete enzymes to break down complex macromolecular compounds and utilize them for growth and metabolism. They can absorb low molecular weight nutrients, produce and se‐ crete secondary metabolites, which are also relatively low molecular weight compounds but not associated with the process of growth and primary metabolism (Bushell, 1989 cited by [4]).

**iv.** *Solubility*: Very slightly soluble in water (10–30 µg mL-1); insoluble in non-polar sol‐

**v.** *Stability*: Unstable to ultraviolet light in the presence of oxygen, to pH extremes (<

**vi.** *Reactivity*: The lactone ring is susceptible to alkaline hydrolysis. Aflatoxins are also

Aflatoxins are quite stable in many foods and are fairly resistant to degradation. The effec‐ tiveness of some processes in reducing concentrations of aflatoxins in food can be affected by many factors, such as the presence of protein, pH, temperature and length of treatment. Commercial processing of raw commodities using cleaning regimes including the removal of broken particles, milling and sorting can reduce aflatoxin concentration considerably [5].

Naturally occurring aflatoxins (as a group) and other 107 agents were evaluated as carcino‐ genic to humans (Group 1). There is sufficient evidence in humans for the carcinogenicity of aflatoxins, being liver cancer (hepatocellular carcinoma) the main effect. Aflatoxin M1, the metabolite of aflatoxin B1 found in milk of lactating mammals was classified in Group 2B as possibly carcinogenic to humans [8]. Carcinogenicity of naturally occurring mixtures of afla‐ toxins B1, G1 and M1 is also demonstrated in experimental animals. The intake of these toxins over a long period of time in very low concentrations may be highly dangerous. These com‐

degraded by reaction with ammonia or sodium hypochlorite.

methanol) and especially in dimethyl sulfoxide

3, > 10) and to oxidizing agents

**Figure 1.** Chemical structures of aflatoxins [7].

vents; freely soluble in moderately polar organic solvents (e.g., chloroform and

Aflatoxins Importance on Animal Nutrition http://dx.doi.org/10.5772/51952 173

Some aflatoxin derivatives are products of animal metabolism following ingestion of the mould metabolites, which are divided into the B and G groups based on their blue or green fluorescence under UV light when absorbed to solid substrates. *A. parasiticus* is the most toxigenic species, the majority of strains producing both B and G toxins (Van Eg‐ mond, 1989a cited by [4]).

Aflatoxins are crystalline substances, freely soluble in moderately polar solvents such as chloroform, methanol, dimethyl sulfoxide; they dissolve in water to the extent of 10-20 mg L-1. Some important physical and chemical properties of aflatoxins are given in Table 1 [5].


**Table 1.** Physical and chemical properties of aflatoxins.

Due to the important structural diversity (Figure 1) of mycotoxins and the variations in their metabolism, it is difficult to edit general rules. Thus, each toxin and respective metabolites have to be investigated as a particular case. The chemical and physical properties of aflatox‐ ins are described as follows [6]:


**2. Aflatoxin properties**

172 Aflatoxins - Recent Advances and Future Prospects

mond, 1989a cited by [4]).

All mycotoxins are low-molecular-weight natural products (i.e., small molecules) (Bennett, 1987 cited [3]). The hyphal structure of filamentous fungi has evolved to utilize solid substrates efficiently by growing over surfaces and penetrating into solid matrices. Moulds are able to se‐ crete enzymes to break down complex macromolecular compounds and utilize them for growth and metabolism. They can absorb low molecular weight nutrients, produce and se‐ crete secondary metabolites, which are also relatively low molecular weight compounds but not associated with the process of growth and primary metabolism (Bushell, 1989 cited by [4]).

Some aflatoxin derivatives are products of animal metabolism following ingestion of the mould metabolites, which are divided into the B and G groups based on their blue or green fluorescence under UV light when absorbed to solid substrates. *A. parasiticus* is the most toxigenic species, the majority of strains producing both B and G toxins (Van Eg‐

Aflatoxins are crystalline substances, freely soluble in moderately polar solvents such as chloroform, methanol, dimethyl sulfoxide; they dissolve in water to the extent of 10-20 mg L-1.

B1 C17H12O6 312 268-269 12,400 21,800 B2 C17H14O6 314 286-289 12,100 24,000 G1 C17H12O7 328 244-246 9,600 17,700 G2 C17H14O7 330 237-240 8,200 17,100

Due to the important structural diversity (Figure 1) of mycotoxins and the variations in their metabolism, it is difficult to edit general rules. Thus, each toxin and respective metabolites have to be investigated as a particular case. The chemical and physical properties of aflatox‐

**i.** *Description*: Colorless to pale-yellow crystals. Intensely fluorescent in ultraviolet

light, emitting blue (aflatoxins B1 and B2) or green (aflatoxin G1) and green–blue (aflatoxin G2) fluorescence, from which the designations B and G were derived, or

**Point**

*UV absorption max* **(ε(L mol***-1 cm-1***)), methanol**

*265 nm 360-362 nm*

Some important physical and chemical properties of aflatoxins are given in Table 1 [5].

**Aflatoxin Molecular formula Molecular weight Melting**

**Table 1.** Physical and chemical properties of aflatoxins.

blue–violet fluorescence (aflatoxin M1)

ins are described as follows [6]:

**ii.** *Melting-points*: see Table 1.

**iii.** *Absorptionspectroscopy*: see Table 1.

Aflatoxins are quite stable in many foods and are fairly resistant to degradation. The effec‐ tiveness of some processes in reducing concentrations of aflatoxins in food can be affected by many factors, such as the presence of protein, pH, temperature and length of treatment. Commercial processing of raw commodities using cleaning regimes including the removal of broken particles, milling and sorting can reduce aflatoxin concentration considerably [5].

Naturally occurring aflatoxins (as a group) and other 107 agents were evaluated as carcino‐ genic to humans (Group 1). There is sufficient evidence in humans for the carcinogenicity of aflatoxins, being liver cancer (hepatocellular carcinoma) the main effect. Aflatoxin M1, the metabolite of aflatoxin B1 found in milk of lactating mammals was classified in Group 2B as possibly carcinogenic to humans [8]. Carcinogenicity of naturally occurring mixtures of afla‐ toxins B1, G1 and M1 is also demonstrated in experimental animals. The intake of these toxins over a long period of time in very low concentrations may be highly dangerous. These com‐ pounds can enter the food chain, mainly, by ingestion through the diet of humans and ani‐ mals (Miraglia et al., 1996 cited by [11]).

Aflatoxins are metabolized in ruminants by the liver and are excreted in the bile. AFB1 in‐ creases the apparent protein requirement of cattle. When significant quantities are con‐ sumed, the metabolite M1 appears in milk within 12 hours. Research suggests M1 is not as carcinogenic or mutagenic as B1, but it does appear to be as toxic as its parent compound [12]. When an animal ingests food contaminated with an AFB1, from 0.5 to 5% of the toxin ingested is biotransformed in the liver into AFM1 (Hussein and Brasel, 2001 cited by [13].

Aflatoxins Importance on Animal Nutrition http://dx.doi.org/10.5772/51952 175

On a worldwide basis about 35% of *A. flavus* strains produce aflatoxins and only the B group. These molds occur in warmer parts of the world and aflatoxins may be produced in a wide range of tropical and subtropical food commodities (Van Egmond, 1989a cited by [4]). The presence of fungi does not necessarily imply the presence of toxins. The fungi species can produce aflatoxins on commodities in the field under stress conditions or in storage when high moisture and warm temperature propitiate their growth (Schuster et al. 1993 cit‐ ed by [11]). The minimum moisture content of foods that allows the growth of *A. flavus* is around 85% relative humidity (0.85 water activity), and temperature of 25-30 ºC. In cereals with high starch conten as rice, maize, sorghum, wheat, barley, the moisture content in the grain is 18-18.5%. The subsequent drying does not affect the existing level of aflatoxin be‐ cause it resists drying and roasting temperatures (Pitted, 1998; Sabino, 1996; Wilson and Payne, 1994 cited by [14]). Because of the weather, aflatoxins are commonly found in South

Time of harvest has been shown to be important in influencing the occurrence and levels of aflatoxin because *Aspergillus* does not compete well with other molds when corn presents more than 20% moisture. Harvesting corn when moisture content is above 20% followed by rapid drying to at least 14% moisture content within 24 to 48 hours of harvest can inhibit *Aspergillus* growth and toxin production. Contaminated grains and their byproducts are the most common sources of aflatoxin. Corn silage may also be a source of aflatoxins, because

On the farm, more than one mold or toxin may be present in the contaminated feed, which of‐ ten makes definitive diagnosis of aflatoxicosis difficult. The prognosis of aflatoxicosis depends upon the severity of liver damage. Once overt symptoms are noticed the prognosis is poor. Treatment should be directed at the severely affected animals in the herd and further poison‐ ing prevented. Aflatoxicosis is typically a herd rather than an individual cow problem. If afla‐ toxicosis is suspected, feed should be analyzed immediately. If aflatoxins are present, the source should be eliminated immediately. Levels of protein in feed and vitamins A, D, E, K and B should be increased as the toxin binds vitamins and affects protein synthesis. Good manage‐ ment practices to alleviate stress are essential to reduce the risk of secondary infections which

Importantly, it has been demonstrated that simple measures can significantly reduce the risk of mycotoxin exposure on farm. Storage of grain at appropriate moisture content (below 130 g

the ensiling process does not destroy toxins already present in silage [12].

America, Africa, Asia and Australia [15].

**3. Aflatoxins occurrence in feeds**

must receive immediate attention and treatment [12].

There is strong evidence that the carcinogenicity of aflatoxins operates by a genotoxic mech‐ anism of action that involves metabolic activation to a genotoxic epoxide metabolite, forma‐ tion of DNA adducts, and modification of the TP53 gene. In humans, hepatocellular carcinomas from areas of high exposure to aflatoxins, up to 50% of tumors have been shown to harbor a specific point mutation in the TP53 tumor suppressor gene [9]. Table 2 shows aflatoxin main producing species and toxic effects, pointed by the International Agency for Research on Cancer (IARC).


**Table 2.** Main producing species and effects of aflatoxins [6,10].

AFB1 is the most potent carcinogenic substance naturally produced by *Aspergillus* species. Indeed, AFB1 is classified by IARC as Group 1 carcinogen [10]. This compound is certainly acutely toxic to humans, is probably responsible for liver necrosis following chronic expo‐ sure, and may be involved in the epidemiology of human liver cancer in some parts of the world perhaps synergistically with hepatitis B virus (Van Egmond, 1989a cited by [4]).

After ingestion, aflatoxin B is metabolized by enzymes to generate a reactive 8,9-epoxide metabolite that can be bound to DNA as well as to serum albumin forming aflatoxin-N-7 guanine and lysine adducts, respectively. Covalent binding to DNA is considered to be a critical step in aflatoxin hepatocarcinogenesis [11].

Determination of these metabolites was solved by developing enzyme linked immunosorb‐ ent assay (ELISA) methods (Vidyasagar et al., 1997 and Nayak, et al., 2001 cited by [11]). The biosynthesis of aflatoxins is induced by sugars. The induction is associated with the tran‐ scriptional activation of the pathway genes and the pathway regulatory gene, aflR. The reg‐ ulation of aflatoxin biosynthesis had been examined by manipulating the transcription of aflR. Studies concerning this topic showed that constitutive overexpression of the pathway transcriptional regulatory gene aflR led to higher transcript accumulation of pathway genes and increased aflatoxin production (Flaherty and Payne, 1997 cited by [11]).

Aflatoxins are metabolized in ruminants by the liver and are excreted in the bile. AFB1 in‐ creases the apparent protein requirement of cattle. When significant quantities are con‐ sumed, the metabolite M1 appears in milk within 12 hours. Research suggests M1 is not as carcinogenic or mutagenic as B1, but it does appear to be as toxic as its parent compound [12]. When an animal ingests food contaminated with an AFB1, from 0.5 to 5% of the toxin ingested is biotransformed in the liver into AFM1 (Hussein and Brasel, 2001 cited by [13].

On a worldwide basis about 35% of *A. flavus* strains produce aflatoxins and only the B group. These molds occur in warmer parts of the world and aflatoxins may be produced in a wide range of tropical and subtropical food commodities (Van Egmond, 1989a cited by [4]). The presence of fungi does not necessarily imply the presence of toxins. The fungi species can produce aflatoxins on commodities in the field under stress conditions or in storage when high moisture and warm temperature propitiate their growth (Schuster et al. 1993 cit‐ ed by [11]). The minimum moisture content of foods that allows the growth of *A. flavus* is around 85% relative humidity (0.85 water activity), and temperature of 25-30 ºC. In cereals with high starch conten as rice, maize, sorghum, wheat, barley, the moisture content in the grain is 18-18.5%. The subsequent drying does not affect the existing level of aflatoxin be‐ cause it resists drying and roasting temperatures (Pitted, 1998; Sabino, 1996; Wilson and Payne, 1994 cited by [14]). Because of the weather, aflatoxins are commonly found in South America, Africa, Asia and Australia [15].
