**3. How to prevent pre-harvest AF?**

rivates [6,7], and even chocolates [8]. In order to find a solution for this problem, some organizations and institutions have purposed prevention strategies in order to reduce the risks given by this public problem especially in low-income countries, but those strategies

The prevalence of AF in crops and livestock is a serious problem in many parts of the world, undermining public health and development efforts. AF are highly toxic, cancer causing fungal metabolites known to cause immune-system suppression, growth retardation, liver disease, and death in both humans and domestic animals. According to the United Nations Food and Agriculture Organization (FAO), 25% of world food crops are affected, and coun‐ tries that are situated between 40ºN and 40ºS are most at risk. Over 4.5 billion people in de‐ veloping countries are at risk of chronic AF exposure [9]. Unless AF levels in crops and livestock are effectively managed, international development efforts to achieve greater agri‐

AF are very stable and persistent, so they are difficult to remove. Due to they are contained in many crops that are consumed by animals, AF have turned into a serious animal problem too. The most susceptible animals are rabbits, turkeys, chickens, pigs, cows and goats [10]. AF can be transmitted from animals to human food (by eggs, meat and dairy) with the con‐

Even non-mouldy foods or raw materials may contain AF. Spores can be transferred by in‐ sects (especially flies, wasps and bees) or by birds to foods where the spores germinate, pro‐ duce mycelium, and AF are excreted. Seeds can contain AF by infection of the egg-cells of the flowering plants. The spores of *A. flavus* and *A. parasiticus* can germinate on the stigma surfaces of plants, then the germ tube penetrates to the developing embryo mimicking pol‐ len germ tubes. The mycelium can establish an endotrophic relationship which is not harm‐ ful for the healthy plant. However, if the plant is under drought stress, then significant levels of AF may be produced in the plant tissue during growth in the field. Under these circumstances food commodities may already be contaminated at harvest and, although the concentrations are never as high as those formed in stored commodities, they can be eco‐

The danger of AF lies in their mode of action by inhibiting the incorporation of precursors for the synthesis of DNA, RNA and proteins; they also block the action of some enzymes that are responsible for the synthesis of nucleic acids, causing centrilobular necrosis in the liver, polymorphonuclear infiltration and fatty degeneration. AF toxicity depends on the dose, the exposure degree, the age, the nutritional status of the animal and the possible syn‐ ergic effects of the chemical agents to which they are exposed [13]. Some secondary metabo‐ lites produced by Aspergillus species are harmful for animals too. That's the case of cyclopiazonic acid (CPA), which causes necrosis of liver or gastrointestinal tissue and ne‐

are not enough to give a real solution to this worldwide daily problem.

cultural development, food security and improve health will be undermined.

**2. The global problem of AF in crops and food**

94 Aflatoxins - Recent Advances and Future Prospects

sequent risk to human health.

nomically significant [11, 12].

crotic changes in skeletal muscle and kidney [14, 15].

It was established in about 1970 that fungal contamination could start in the field before har‐ vest [9]. Although the highest levels of AF are undoubtedly associated with post-harvest spoilage of food commodities stored under inappropriate conditions of water activity and temperature, the aflatoxigenic fungi have more complex ecologies [12]. Factors that influ‐ ence the incidence of fungal infection and subsequent toxin development include inverte‐ brate vectors, grain damage, oxygen and carbon dioxide levels, inoculum load, substrate composition, fungal infection levels, prevalence of toxigenic strains and microbiological in‐ teractions. Insect damage on crops allows fungi to access in them, increasing the chances of AF contamination, especially when loose-husked maize hybrids are used [18, 19].

Controlling or reducing infection by regulating the factors that increase the risk of AF con‐ tamination in the field contributes extensively in managing AF. Management practices that reduce the incidence of AF contamination in the field include timely planting, maintaining optimal plant densities, proper plant nutrition, avoiding drought stress, controlling other plant pathogens, weeds and insect pests and proper harvesting [20]. Pre-harvest measures that are efficient in reducing AF levels are the same as those that will enhance yields. Crop rotation and management of crop residues also are important in controlling *A. flavus* infec‐ tion in the field. Tillage practices, fertilizer application, weed control, late season rainfall, ir‐ rigation, wind and pest vectors affect the source and level of fungal inoculum, maintaining a disease cycle in crops like maize [19, 21]. Lime application, use of farm yard manure and ce‐ real crop residues as soil amendments have shown to be effective in reducing *A. flavus* con‐ tamination as well as AF levels by 50-90%. Calcium, which is part of lime, thickens the cell wall and accelerates pod filling, while manure facilitates growth of microorganisms that suppress soil infections [21].

In order to minimize the levels of AF and mycotoxins in general, the National Institute of Agricultural Technology of Argentina (INTA), recommends to make early plantings, to plant resistant genotypes, to do good farming practices, to avoid stress conditions, to mini‐ mize insect damage, to harvest early in order to avoid delays, to avoid damaged kernels and to storage at less of 13% moisture in a clean, fresh and airy place with no insects [22]. As mentioned before, it is important to avoid product moisture, high temperatures (between 25 and 32°C) and high relative humidity in storage and seeds preservation. Weeds have to be removed and crop rotation should be done routinely. Prior to the preparation of the ground, dead organic matter has to be disabled or burned; product mechanical damage has to be avoided; crops have to be collected at full maturity; storage places should be dry and the entry of water has not to be allowed; storage health standards have to be fulfilled (pallets, proper humidity levels, adequate ventilation and lighting, etc.), and periodic inspection of the stored product should be done [23].

By the other hand, cleaning of stores before loading in the new harvests has been correlated with reduction in AF levels. Separating heavily damaged ears (those having greater than 10% ear damage) also reduces AF levels in crops like maize. Wild hosts, which constitute a major source of infestation for storage pests, should also be removed from the vicinity of stores. For some crops like peanuts, the standard practice is drying of pods in the sun. Often pods are left in the field after uprooting for up to four weeks to partially dry prior to home

Novel Methods for Preventing and Controlling Aflatoxins in Food: A Worldwide Daily Challenge

http://dx.doi.org/10.5772/50707

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AF are unevenly distributed in a seed lot and may be concentrated in a very small percent‐ age of the product. Sorting out of physically damaged and infected grains (known from col‐ orations, odd shapes and size) from the intact commodity can result in 40-80% reduction in AF levels [19]. The advantage of this method is that it reduces toxin concentrations to safe levels without the production of toxin degradation products or any reduction in the nutri‐ tional value of the food. This could be done manually or by using electronic sorters. Some studies have also looked at the use of local plant products for the control of fungi mostly proving their efficacy in-vitro but these products have not been sufficiently tested for their

Although natural methods are cost-effective, the fungal contamination in grains is often un‐ avoidable, so there is the need to apply a suitable process to inactivate the toxin. Sorting can remove a major part of AF contaminated units, but levels in contaminated commodities may also be reduced through physical food processing procedures like dehulling (which reduces AF contamination by 92%), roasting, baking, frying, X-radiation, extrusion cooking and nix‐ tamalization, being the last two the most studied because of their effectiveness [27-29].

Roasting, baking and frying are three common methods used in some low-income countries, and all of them involve heath. Nevertheless, the heat used as the only factor for the myco‐ toxins destruction is ineffective because the temperatures reached during the detoxification process affect vitamins and food proteins. In contrast, heath can be used for increase the re‐ active capacity of some food molecules such as acids, alkalis and other chemical agents [30].

Radiation has also been used against AF. X-rays are capable of producing a high issuance of energy, which causes the breakdown of stable molecular structures. It has been established

Extrusion cooking is a processing technology that involves pushing a granular food material down a heated barrel and through an orifice by a rotating, tight fitting Archimedean screw. The shear forces created by the rotating action of the screws, together with frictional, com‐ pressive and pressure forces provide the necessary environment for rapidly cooking and transforming the food into visco-elastic melt. Extrusion cooking is an efficient high tempera‐ ture short time process, and it is used to produce a wide variety of foods and ingredients. To destroy or inactivate AF, the extrusion cooking conditions need to be severe (high shear, high temperature, and the right pH) in order to provide the necessary environment in the

drying [19].

**4.2. Physical methods**

efficiency in controlling AF in stored crops [19, 26].

that AFB1 and AFG1 are the most sensitive to X-rays [30, 31].

To avoid risks to human and animal health, INTA also suggests to avoid feeding animals with crops in poor condition (especially corn), not to use fractions of discarded corn fodder, and to make good manufacturing practices [22].
