Implication of Aflatoxin Contamination in Agricultural Products

Ephrem Guchi

  Open Access OPEN ACCESS  Peer Reviewed PEER-REVIEWED

Implication of Aflatoxin Contamination in Agricultural Products

Ephrem Guchi

Department of Applied Biology, Samara University, School of Natural and Computational Sciences, Samara, Ethiopia

Abstract

Aflatoxins are secondary fungal metabolites that contaminate agricultural commodities and can cause sickness or death in humans and animals. Risk of aflatoxin contamination of food and feed in Africa is increased due to environmental, agronomic and socio-economic factors. Temperature, food substrate, strain of the mould and other environmental factors are some parameters that effect mycotoxin production. Preventing mycotoxin production at farm level is the best way to control mycotoxin contamination. Advances in molecular techniques and other decontamination methods such as gamma-irradiation and microwave heating could help to deal with these issues. Mycotoxins could be used as an energy source for a group of aerobic microorganisms, which are suitable to mycotoxin biodegradation. Several protocols have been provided to biodegrade mycotoxins in food and feed using potential bacteria such as Lactobacillus and Bifidobacterium. However, there are varieties of responses between different microorganisms against mycotoxins. For example, Bacillus brevis were not affected by high concentrations of trichothecene. Application of microorganisms needs to be evaluated from a safety point of view. Application of microorganisms on mycotoxin degradation, food and feed materials also need to be investigated. Further studies need to be conducted to address the seasonal variation of aflatoxin contamination in food and feed. Understanding the seasonal variation could help demonstrate and develop more effective decontamination methods. For example, it is postulated that mycotoxin issues due to monsoons in Hungary could possibly be concluded to technical difficulties in pre- and post-harvest operations. Application of advanced methods such as DNA biosensors and infrared spectroscopy for rapid and accurate detection of mycotoxin and related fungi is increasing dramatically. Application of new and advanced detection techniques could enable the agricultural industry to deal more effectively with the occurrence of aflatoxin contamination.

Cite this article:

  • Guchi, Ephrem. "Implication of Aflatoxin Contamination in Agricultural Products." American Journal of Food and Nutrition 3.1 (2015): 12-20.
  • Guchi, E. (2015). Implication of Aflatoxin Contamination in Agricultural Products. American Journal of Food and Nutrition, 3(1), 12-20.
  • Guchi, Ephrem. "Implication of Aflatoxin Contamination in Agricultural Products." American Journal of Food and Nutrition 3, no. 1 (2015): 12-20.

Import into BibTeX Import into EndNote Import into RefMan Import into RefWorks

1. Introduction

Aflatoxins are a group of mycotoxins produced by Aspergillus species, including A. flavus, A. parasiticus, and A. nomius. A quarter of the world’s food crops are estimated to be affected by mycotoxins; creating a large economical loss in the developed and developing countries (Kumar and Rajendran, 2008). Other reports indicate even higher contamination rate of aflatoxin (Njobeh et al., 2009). Exposure to higher levels of aflatoxin contamination increases cancer incidence, including risk of hepato-cellular carcinoma especially in 6- to 9-year-old girls and neural tube defects (Umoh et al., 2011).

One of the reasons which make aflatoxins one of the most challenging mycotoxin is the fact that it could be produced by the responsible fungi not only at pre-harvest time but also at post harvest stages including storage. However, later on, lack of regulations or poor enforcement, which makes the use of such contaminated commodities inevitable, could lead to severe human and animal diseases too. Aflatoxin B1, B2, G1 and G2 are the most important members of the aflatoxin group, which chemically are coumarin derivatives with a fused dihydrofurofuran moiety. Presence of aflatoxin B1, B2, G1 and G2 may naturally occur in different ratios depending on different matrices. However, it was concluded that when aflatoxins are limited only to AFB1 and AFB2, such ratio is 1.0 to 0.1, while when all four aflatoxins occur (AFB1, AFB2, AFG1 and AFG2), they may be found in a ratio of 1.0:0.1:0.3:0.03 (Abbas et al., 2010). Cereals notably corn, nuts such as peanuts, pistachio and Brazil nuts, oil seeds such as cottonseed, as well as copra, the dried meat of coconut, are some of the commodities with greater risk of aflatoxin contamination (Cornea et al., 2011; Idris et al., 2010). Because peanuts, cottonseed and copra constitute the most important source of edible oils, they are of particular interest (Idris et al., 2010). Commodities which are resistant or only moderately susceptible to aflatoxin contamination in the field include wheat, oats, millet, barley, rice, cassava, soybeans, beans, pulses and sorghum. However, when any of these commodities are stored under high moisture and temperature conditions, aflatoxin contamination may occur (Smith and Moss, 1985). Other commodities such as cocoa beans, linseeds, melon seeds and sunflower seeds have been infrequently contaminated with mycotoxins with lower importance rate compared to other commodities (Bankole et al., 2010). Aflatoxin is the single most important contaminant on The Rapid Alert System for Food and Feed (RASFF) of the European Union in a way that in 2008, aflatoxins alone were responsible for almost 30% of all the notifications to the RASFF system (902 notifications) (Energy, 2009). With increasing knowledge and awareness of aflatoxins as a potent source of health hazard to both human and animals, a great deal of effort has been made to completely eliminate the toxin or reduce its content in foods and feedstuffs to significantly lower levels. Although prevention is the most effective intervention, chemical, biological and physical methods have been investigated to inactivate aflatoxins or reduce their content in foodstuffs (Rustom, 1997).

2. Natural Occurrence of Aflatoxin Contamination in Raw Agricultural Products

Natural occurrence of aflatoxins in raw agricultural products poses severe health and economic risks worldwide. The Food and Agriculture Organization (FAO) estimates that many basic foods could be contaminated with mycotoxin producing fungi, contributing to huge global losses of foodstuffs, about 1000 million metric tons each year (Bhat and Karim, 2010). Contamination of feed materials with mycotoxins is an important issue for farmers due to both acute and chronic intoxication in animals. The economic impact of feed contamination with mycotoxins includes productivity reduction and organ damage (Upadhaya et al., 2010). Aflatoxins, zearalenone, trichothecenes, fumonisins and ochratoxin A are the most frequently investigated toxins, although there are more than 300 recognized mycotoxins in animal feed (Rustemeyer et al., 2010). Mycotoxin contamination reports in animal feed indicate a variety of contamination levels (Monbaliu et al., 2010). Fungi which produce mycotoxin belong to Aspergillus, Penicillium and Fusarium species (Rustemeyer et al., 2010). Aspergillus and penicillium constitute a major part of the fermented feed microbiota (Roige et al., 2009). Intrinsic and extrinsic factors during storage and at field condition may interact with mycotoxin contamination. Animal feeds, such as hay and straw, might be contaminated during pre-harvest or drying stages (Bhat and Karim, 2010). Mycotoxin contaminated animal feed cause’s serious effect on monogastric animals. However, the ruminants may be more resistant to mycotoxins due to biotransformation ability of the rumen microbiota. Other factors such as age, aflatoxin concentration and duration of exposure might also have some effect (Rustemeyer et al., 2010; Upadhaya et al., 2010). The affected commodities by aflatoxins are corn, peanuts, cottonseed, millet, sorghum and other feed grains. In ruminants, a part of aflatoxin B1 is degraded into aflatoxicol and the remaining is hydroxylated in the liver into aflatoxin M1 (Upadhaya et al., 2010). Aflatoxin B1 is considered as a group I carcinogen for humans by International Agency for Research on Cancer (IARC) (Seo et al., 2011). Aflatoxicosis may cause death in ruminants (Pierezan et al., 2010). Despite extensive research done during the last few decades, which helped authorities around the world to establish control measures, still aflatoxin contamination in food and agricultural commodities remains as one of the most challenging and serious food safety problem.

Close study of the annual reports in the last decade (2003-2009) of the Rapid Alert System for Food and Feed (RASFF) showed four aforementioned groups contributed to the most aflatoxin contamination. Although, one should be careful in jumping to a bigger conclusion as these data also depends on the policy of EU countries, on products that go on a 100% check and those checked randomly. The detailed results are included in Table 1. According to a study by Vinod et al. (2008) the incidence of mycotoxins in some commercially important agricultural commodities concluded that high-risk commodities for mycotoxin contamination were corn and groundnut.

Table 1. Comparison of number of aflatoxin allert notifications according to product category reports in the RASFF system in years 2003–2009

2.1. Nuts, Nut Products and Seeds

As it is clear from Table 1 based on RASFF reports; nuts, nut products and seeds were the most rejected lots, and thus the most contaminated products in general too. These serve as very good substrates due to their high fat content. Also, aflatoxin producing fungi can cause toxin production in all steps including pre-harvest, drying process as well as storage. Environmental conditions such as prolonged drought stress play a major role in increasing the risk of aflatoxin contamination (Kumar and Rajendran, 2008). Similar conclusion was also drawn by Wagacha & Muthomi (2008) from the African perspective too, in which aflatoxins widely occured in groundnuts. A close study of all mycotoxins rejected lots (1000 reports of 5979 at the time) based on online available information of RASFF from 16/12/2009 till 02/05/2011 revealed that highest aflatoxin levels were found again in this group (Table 2).

A Korean survey of different nuts and their products marketed in South Korea showed that 9 out of 85 samples including peanuts, peanut butter, and pistachios were contaminated with aflatoxins (10.6% of incidence). The most contaminated nut was peanut (roasted) with values ranging from 2.00–28.24 µg/kg and a mean of 10.67 ± 12.30 µg/kg for total aflatoxins (7.97 ± 7.75 µg/kg for aflatoxin B1). Similar data at slightly lower levels was found in one assorted nuts and 2 peanut butter samples (Chun et al., 2007). A Turkish study conducted from September 2008 to February 2009, detected aflatoxin B1 contamination in almost 49.2% (59/120) of un packed and packed pistachio nut samples at levels lower than action limits of 5 μg/kg (Set and Erkmen, 2010). Abdulkadar et al. (2004) found aflatoxin B1 contamination in different nuts in the range of not detected (ND)–81.64 μg/kg. In a study by Ismail et al. (2010), from about 196 nuts and their products in Malaysia, 16.3% of the products showed contamination between 17.2 to 350 μg/kg. Forty-eight samples out of 95 were contaminated within a range of 0.007 to 7.72 µg/kg in pistachio nuts (Set and Erkmen, 2010).

Table 2. Some of the highest values of aflatoxin contamination in the rejected lots of Nuts, nut products and seeds, based on The Rapid Alert System for Food and Feed (RASFF)

2.2. Fruits and Vegetables

Close study of all mycotoxin rejected lots (277 reports of 672 at the time) from 01/01/2008 till 19/04/2011, based on online information from RASFF, revealed that highest aflatoxin levels were found in dried figs from Turkey followed by dried figs from Greece (Table 3). Natural occurrence of aflatoxin in fruits came to light more in the recent years.

Table 3. Some of the highest values of aflatoxin contamination in the rejected lots of fruit and vegetables, based on The Rapid Alert System for Food and Feed (RASFF)

Reports indicated that figs, dates and citrus fruits grown in susceptible regions (the high temperature conditions) could get contaminated with aflatoxins (Rivka, 2008), of which fig is most vulnerable to aflatoxin contamination. The reason for such high susceptibilities apart from their chemical properties is based on the fact that A. flavus is able to enter and colonize in the internal cavity of the fruit (Rivka, B., 2008). Although some surveys found only trace amount of aflatoxins in fig (Blesa et al., 2004), others found quite high levels and the contamination levels might go as high as 77,200 ng/g. Aflatoxins were also reported, but in lesser extent, in other fruits such as dates, citrus fruits, raisins and olives (Ferracane et al., 2007). In case of citrus fruits, at least there is sound evidence of potential contamination risk (Bamba and Sumbali, 2005).

2.3. Cereal Products

A study was conducted in Iran on Aflatoxin contamination of foodstuffs. Fifty-one maize samples, intended for animal feed and human consumption, were collected from the four main maize production provinces in Iran and analyzed by high-performance liquid chromatography for contamination by four naturally occurring aflatoxin analogues (AFB1, AFB2, AFG1, and AFG2). AFB1 was detected in 58.3% and 80% of the maize samples obtained from Kermanshah and Mazandaran provinces, respectively (Ghiasian et al., 2011).

High levels of aflatoxin B1 contamination in rain-affected maize and rice at a level of 15600 and 1130 µg/kg respectively, was reported. Also, high levels of aflatoxins were found in parboiled rice (max 130 µg/kg). However, relatively lower values were reported in normal crops (Vasanthi, 1998).

The crops with higher risk of aflatoxin contamination were groundnuts, maize and chilies. In one study, 21% and 26% of groundnuts and maize samples respectively, exceeded their national maximum limit of 30 µg/kg of aflatoxin contamination (Vasanthi, 1998).

Vargas et al. (2001) reported that 38.3% of maize samples were contaminated with aflatoxin B1 with a mean of 9.4 µg/kg and a maximum of 129 µg/kg. The investigators have reported that only 3.7% showed levels above 20 µg/kg. They found the co-occurrence of aflatoxin B1 and fumonisin B1 in all of the 82 aflatoxin-contaminated samples. Co-occurrence of these 2 mycotoxins with zearalenone was observed only in 18 samples.

Maize and groundnuts were reported to be a major source of aflatoxin contamination around the globe particularly in India, South America and the Far East in the late 1990’s. Other commodities which raised concerns with regard to high susceptibility to aflatoxin contamination were tropical and subtropical cereals, oilseeds, and tree nuts as well as cotton-seed meal.

The largest and the most severe documented aflatoxin poisoning has been reported at a level as high as 8,000 µg/kg in Kenya in 2004, causing 125 deaths out of 317 case-patients (Wagacha and Muthomi, 2008).

According to a study conducted by Sugita-Konishi et al. (2006) about the contamination in various Japanese retail foods with aflatoxin B1, B2, G1, and G2, and other mycotoxins, between 2004 and 2005, aflatoxins were detected only in almost half of the peanut butter samples with the highest concentration of aflatoxin B1 at about 2.59 µg/kg. While in other products such as corn products, corn, peanuts, buckwheat flour, dried buckwheat noodles, rice, or sesame oil, aflatoxin contamination was not detected.

Aflatoxin was also detected in the majority of dried yam chips samples surveyed in Benin with levels as high as 220 μg/kg, although the average was much lower (14 μg/kg). More than 54% of dried yam chips in Nigeria were found positive for aflatoxin contamination, while high levels of aflatoxins ranging from 10–120 μg/kg was detected in slightly more than one third of the tiger nut (Cyperus esculentus) samples in the same country (Bankole and Mabekoje, 2004).

High aflatoxin levels in maize, in some other African countries, notably Benin and Togo have been reported and one third of the household grain, contained aflatoxins in the range of five-fold the safe limit (Wagacha and Muthomi, 2008).

Maize (Zea mays L.) grain was shown to be a good substrate for mould infection including A. flavus, A. parasiticus and production of aflatoxins. Indian scientists have reported several cases of aflatoxin epidemic in humans over the last decade mainly due to the consumption of heavily contaminated maize that nominates maize as a high risk crop. Rice is another member of the cereal family which shows high level of aflatoxin contamination, as high as 2830 μ g/kg, which according to some reports was even higher than levels compared to wheat and maize. Aflatoxin contamination in rice occurs in the preharvest stage. Delayed drying as well as high moisture content and crop storage can cause postharvest contamination. Although both white rice and parboiled rice could be contaminated with aflatoxin, parboiled rice (boiled rice in the husk), despite improvement in its nutritional profile especially its vitamin-B content (Beri-beri disease is common among the white rice-eating people), is more suitable for the storage fungi to enter if later drying is not adequate (Kumar and Rajendran, 2008). Nguyen et al. (2007) investigated the possible coexistence of aflatoxin B1, citrinin and ochratoxin in Vietnam. From 100 rice samples collected countrywide, 35 samples showed values higher than the limit of quantification (LOQ) of 0.22 µg/kg, with a mean of 3.31 µg/kg and a highest value of 29.8 µg/kg, for aflatoxin B1. The results also indicated a high percentage in co-occurrence of aflatoxin B1 and ochratoxin A in rice. Their findings showed significant effect of monsoons that increased the average of quantifiable samples of AFB1 and the ratio of detectable samples in rice, compared to those in the dry season. In some provinces, these were 5 times higher (mean of 10.08 µg/kg compared to 1.77 µg/kg) or even more (mean of 4.5 µg/kg compared to less than LOQ of 0.22 µg/kg). Given the average daily intake of rice by aVietnamese adult to be 500 g, there is a cause for concern (Nguyen et al., 2007). Reports raised concern over the presence of citrinin in red yeast rice (Monascus fermented rice); a traditional natural food colorant in Asia, while no reports on aflatoxin was obtained (Lin et al., 2008). A study on Turkish wheat samples published in 2008 revealed 60% contamination level in a very low range indeed (maximum of 0.644 μ g/kg) (Giray et al., 2007).

No aflatoxin was found in the 60 samples of corn meal and flour obtained from Sao Paulo Market in 2000 (Bittencourt et al., 2005). A market research of various food products (cereal and cereal products, nuts and nut products, spices, dry fruits and beverages) in Qatar in 2002, revealed no detected levels of aflatoxin contamination in rice and wheat (Abdulkadar et al., 2004).

The highest aflatoxin levels were found in stone ground corn meal from India followed by mixed snacks from India, and rice from Thailand. Aflatoxin contamination in raw and processed food can be monitored using chromatography or antibody platforms (Seo et al., 2011). Aflatoxin B1 was detected at the following levels in all samples of Nigerian grains: 17.01-20.53 μ g/kg in wheat, 34.00-40.30 μ g/kg in millet, 27.22-36.13 μ g/kg in guinea corn, and 40.06-48.59 μ g/kg in bread fruit (Odoemelam and Osu, 2009).

Close study of all mycotoxins rejected lots (249 reports of 249 at the time) from 14/02/2000 till 28/04/2011, based on online information available from RASFF, revealed that the third highest aflatoxin levels were found in this group (Table 4).

2.4. Herbs and Spices

Medicinal plants are various plants with medicinal properties, which were the core of traditional therapy for the most of human history. Although the toxic effect of some were known for centuries, only in the recent modern time, the safety of these plants from the contamination point of view come to light.

Table 4. Some of the highest values of aflatoxin contamination in the rejected lots of cereals and cereals products, based on The Rapid Alert System for Food and Feed (RASFF)

One of the safety concerns in herbal medicine now a days is the presence of mycotoxins, notably aflatoxins, as their use have been increasing in the recent years after a decline in their use for almost a century. It has been reported that spices and herbs that was used for the improvement of some forms of liver disorder might be contaminated with high concentrations of aflatoxins, with aflatoxin B1 at an alarming level of 2230 µg/kg (Moss, 1998). Abdulkadar et al. (2004) found aflatoxin B1 contamination in mixed spices powder in the range of 0.16–5.12 μg/kg, while chilli powder showed a higher range of 5.60–69.28 μg/kg.

A Turkish study conducted from September 2008 to February 2009, detected aflatoxin B1 contamination in 80% (48/60) of unpacked and packed ground red pepper samples within the range of 5-55.9 μg/kg (Set and Erkmen, 2010). Zinedine et al. (2006) reported relatively low contamination levels in spice samples including paprika; ginger, cumin, and pepper. The highest level of aflatoxin was found in red paprika (9.68 μg/kg) (Zinedine et al., 2006). Close study of all mycotoxin rejected lots (211 reports of 432 at the time) from 06/12/2007 till 19/04/2011, based on online information available from RASFF, revealed that the highest aflatoxin levels were found in curry powder from Nigeria, whole nutmeg from Indonesia, dried paprika from Peru and suya pepper from Ghana, followed by paprika powder from UK (Table 5). Contrary to the long history and the wide use of herbal medicines, there are only a few publications in regard to their mycotoxin contamination compared to the large number of publications on the contamination of cereals and oil seeds (Trucksess & Scott, 2008). The European Pharmacopeia has set limits for aflatoxin B1 and total aflatoxins at 2 and 4 µg/kg respectively, for some medicinal herbs (Pharmacopeia, 2007). Although in one study in South Africa, no aflatoxin contamination was found in some medicinal plants (Sewram et al., 2006), while others reported levels ranging from 2.90–32.18 µg/kg (Yang et al., 2005). Roy et al. (1988) reported both high incidence (>93%) and high levels ranging from 90–1200 µg/kg in some common drug plants. Piper nigrum with a concentration of 1200 µg/kg was the highest contamination level reported. The second highest reported value was in the seeds of Mucuna prurita at a level of 1160 µg/kg. The third highest value was 1130 µg/kg, which found in the roots of Plumbago zeylanica (Roy et al., 1988). Aflatoxins were only found in 1 out of 5 Aerra lanata medicinal plant samples from Sri Lanka at 500 µg/kg (Abeywic et al.,1991). In another survey in India, 60% samples of medicinal plant seeds were contaminated with AFB1, ranging from 20 to 1180 µg/kg (Trucksess and Scott, 2008). In Thailand, five out of 28 herbal medicinal products were found to be contaminated with aflatoxins at 1.7–14.3 µg/kg using an immunoaffinity column (IAC) and high performance liquid chromatography (HPLC) method (Tassaneeyakul et al., 2004). None of the samples contained aflatoxins at levels above 20 ng/g (Tassaneeyakul et al., 2004). In Malaysia and Indonesia, 16 of the 23 commercial traditional herbal medicines, jamu and makjun, analyzed using IAC/LC method contained a low level of total aflatoxins (0.36 µg/kg) (Ali et al., 2005). Romagnoli et al. (2007) analyzed aflatoxins in 27 aromatic herbs, 48 herbal infusions and medicinal plants using LC with post-column derivatization and fluorescence detection. They found no contamination with aflatoxins (Romagnoli et al., 2007). In a study by Hitokoto et al. (1978) aflatoxins were not detected in the 49 powdered herbal drugs, Ten percent of the tablets of Cascara sagrada dried bark were contaminated with aflatoxins in Argentina.

In a study on garlic samples, no aflatoxins were found at levels >0.1 µg/kg. However, aflatoxin levels between 4.2-13.5 µg/kg were detected in ginger (Patel et al., 1996).

A detailed UK study of aflatoxin contamination in some herbs and spices including curry powder, pepper, cayenne pepper, chilli, paprika, ginger, cinnamon and coriander showed 95% contamination below 10 μg/kg of total aflatoxins, while only 9 out of the 157 retail samples had higher levels (Macdonald & Castle, 1996). Study of ginseng root samples, both simulated wild and cultivated ones by D’Ov idio et al. (2006), showed approximately 15 µg/kg of total aflatoxins in only 2 of the simulated wild roots while none of the cultivated roots were contaminated with aflatoxins. Similar results (16 µg/kg) were found in just one mouldy ginseng root purchased from a grocery store (D'Ovidio et al., 2006). Trucksess and Scott (2008) found that 30% of the ginseng products purchased in USA was contaminated with AFB1 at levels of about 0.1 µg/kg. In an aflatoxin survey done in Turkey, 17.1% and 23.1% of unpacked and packed ground red peppers respectively, were contaminated with total aflatoxins and aflatoxin B1, with one out of the 82 samples over the legal limit (Set and Erkmen, 2010).

Table 5. Some of the highest values of aflatoxin contamination in the rejected lots of herbs & spices, based on The Rapid Alert System for Food and Feed (RASFF)

3. Aflatoxigenic Fungi

Aflatoxins are produced by four Aspergillus species. These include Aspergillus flavus Link ex Fr, Aspergillus nomius Kurtzman, Horn and Hesseltine, Aspergillus parasiticus Speare, and Aspergillus tamarii (Goto et al., 2013). The agronomically and economically most important aflatoxin producers are the closely related A. flavus, hence the name afla-toxin, and A. parasiticus. Both species are soil-borne fungi that grow on living and decaying plant matter. These fungi produce aflatoxins on various commodities, but they are a concern on corn, groundnut and cottonseed. A. flavus can be distinguished from A. parasiticus by its smooth spores and yellow-green colonies on potato dextrose agar (PDA) medium. A. parasiticus produces dark yellow-green conidia with nearly spherical vesicles that produce roughened conidia. It can be readily distinguished from A. flavus by its rough-walled conidia (Goto et al., 2013).

Dominant aflatoxins produced by A. flavus are B1 and B2, whereas A. parasiticus produces two additional aflatoxins G1 and G2 (Goto et al., 2013). A. flavus of the section Flavi is the most common species involved in pre-harvest aflatoxin contamination of crops and causes aflaroot or yellow mould. A. flavus is the most common mycotoxin-producing fungus found in groundnuts; this is true across various climates and geographic regions.

Aflatoxigenic fungi are soil-borne imperfect filamentous fungi, which are saprophytic during most of their life cycle, and grow on wide variety of substrates, including decaying plant and animal debris. Two major factors that influence soil populations of these fungi are soil moisture and soil temperature. These storage fungi can grow at temperatures ranging from 12 to 48 oC, with optimum of 25 to 42 ºC, and at water potentials as low as -35 MPa. Under high soil temperatures and low moisture, which are associated with drought stress, these fungi become highly competitive and dominant, produce abundant inocula, and outcompete other microflora on corn, cotton, and groundnut (Goto et al., 2013).

Neither A. flavus nor A. parasiticus has a known sexual stage; they reproduce only by asexual means but undergo genetic recombination through a parasexual cycle. Morphology of the conidiophore, which bears asexual spores, is the most important taxonomic character in the identification of Aspergillus. Other important morphological structures used in identification are cleistothecia, hulle cells, and sclerotia (Bennett, 2013). These fungi can survive either as mycelium or as resistant structures known as sclerotia. A. flavus type fungi are genetically and phenotypically diverse. There are of two types, L isolates producing abundant conidiophores, large sclerotia, and variable amounts of aflatoxin, while the S isolates produce abundant, small sclerotia, fewer conidiophores, and high levels of aflatoxins.

Aflatoxigenic fungi are ubiquitous in nature and have important roles in natural ecosystems and human economy. Aspergillus species are capable of recycling starches, hemicelluloses, celluloses, pectins and other sugar polymers. Some species of Aspergillus degrade more refractory compounds, such as fats, oils, chitin and keratin. Maximum decomposition occurs in the presence of sufficient nitrogen, phosphorus and other essential inorganic nutrients. Foods utilized by humans and domestic animals are also good nutritional sources for Aspergillus species (Bennett, 2013).

3.1. Life Cycle of Aspergillus Species

Aspergillus flavus is a saprophytic fungus that survives on dead plant tissue and sometimes behaves as a weak and opportunistic pathogen (Yu et al., 2012). The sources of inocula for A. flavus and A. parasiticus are sporogenic sclerotia, conidia and mycelia that over-winter in plant debris (Scheidegger and Payne, 2012). In fields repeatedly cropped to groundnut or rotated between groundnut, maize and cotton, conidia from sporogenic sclerotia are the primary source of A. flavus inocula. Conidia adjacent to the developing groundnut pods germinate in the soil following the release of carbon and nitrogen substrates by injured groundnut pegs and result in colonization of the pods. Hot humid conditions favor the release of spores on plant residues, and these spores are dispersed by wind through the field (Scheidegger and Payne, 2012). Conidia that adhere to insect bodies are physically moved to plant parts and flowers in groundnut. Smaller, generally immature kernels are more easily infected in a shorter period of time than kernels in more mature pods. Infections of groundnut kernels at other maturity stages are relative to the survival of the fungus and not necessarily to a new infection at a later stage of maturity. Aspergillus flavus does not always establish a successful systemic infection in groundnut plants.

4. Methods of Detecting Aflatoxins

The above stated agricultural products were analyzed for aflatoxin contamination using ELISA test. A total of 300g from each sample was grind to a 1mm particle size using laboratory mill (Thomas- WILEY, LABORATORY MILL, Model 4. ARTHUR H. THOMAS Company PHILADELPHIA, PA., U.S.A.). About 100g of each sample was taken to Haramaya University Plant Sciences laboratory, Haramaya, Ethiopia, for aflatoxin analysis. Then 5g of groundnut flour from each sample was blended to 25 ml of 70% methanol. The extractions was done by mixing the solution with magnetic stirrer or soft shaking over a 10min period by flask shaker until the powder was thoroughly pulverized. The obtained solution was filtered through a Whatman No. 1 (Whatman International Ltd. Maidstone, UK) filter paper and 15 ml of distilled water and 0.25 ml of Tween20were added to 5ml of the filtered solution. The resulting suspension was then stirred for 2 minby vortex mixer. Immuno affinity column (RIDA® Aflatoxin column) (Art No: R5001, ArtNo: R5002, RBiopharm AG, Darmstadt, Germany) was used for sample clean up prior to analysis of aflatoxin. The columns were rinsed with 2ml of distilled water and filled with 1ml of the extracted samples solutions. The suitable adopter was attached on the top of column and syringe was used as sample reservoir. The samples passed slowly and continuously through the columns (approximately 1 drop/sec) and the syringes were filled with residual samples solutions. The passed solutions were discarded and the columns were rinsed by 10 ml of distilled water. This was repeated again and some air was pressed through the column and absorbed with light - 32 -vacuum (approximately 10 sec) to make sure that all the residual fluids were removed from the columns. Then the syringe was removed and placed on a clean and closable vial directly below the column and eluted with 0.5 ml of 100% methanol (methanol had to passed slowly through the column at flow rate of approximately 1 drop/sec) to ensure complete elution of the aflatoxins. All eluted residues were collected by pressing air thoroughly through the column to vials.

4.1. Aflatoxin Analysis by ELISA

Aflatoxin analysis was carried out using the ELISA (RIDASCREEN® Aflatoxin total Enzyme Immunoassay for the quantitative analysis of Aflatoxin R-Biopharm AG, Darmstadt, Germany) according to the manufacture’s recommendation. Fifty µl of the standard solutions and prepared samples were transferred to each well of the micro-titer plate in duplicate. Then 50µl of enzyme conjugate and 50 µl of the antibody solution were added to each well, and the contents of the wells were mixed gently by shaking the platemanually. After incubation for 30 min at room temperature (20-25°C) in the dark, the wells were emptied by inverting the microwell holder upside down and tapping it vigorously against absorbent paper. This was followed by washing the wells with 250 µl washing buffer two times, 100µl of substrate (Chromogen) was added to each well, mixed gently by shaking the plate manually, and the reaction was stopped by adding 100µl of stop solution into each well aft er 15min incubation at room temperature in the dark. Finally, absorbance of each well was measured by ELISA reader (Multiscan Ex microplate photometer; Thermo Electron Corporation, Vantac, Finland) at 450 nm within 30 min after addition of stop solution. Toxin concentration was read directly from the standard curve.

5. Summary

Temperature, food substrate, strain of the mould and other environmental factors are some parameters that effect mycotoxin production. Preventing mycotoxin production at farm level is the best way to control mycotoxin contamination. Advances in molecular techniques and other decontamination methods such as gamma-irradiation and microwave heating could help to deal with these issues. Mycotoxins could be used as an energy source for a group of aerobic microorganisms, which are suitable to mycotoxin biodegradation. Several protocols have been provided to biodegrade mycotoxins in food and feed using potential bacteria such as Lactobacillus and Bifidobacterium.

However, there are varieties of responses between different microorganisms against mycotoxins. For example, Bacillus brevis were not affected by high concentrations of trichothecene. Application of microorganisms needs to be evaluated from a safety point of view. Application of microorganisms on mycotoxin degradation, food and feed materials also need to be investigated. Further studies need to be conducted to address the seasonal variation of aflatoxin contamination in food and feed. Understanding the seasonal variation could help demonstrate and develop more effective decontamination methods. For example, it is postulated that mycotoxin issues due to monsoons in Hungary could possibly be concluded to technical difficulties in pre- and post-harvest operations. Application of advanced methods such as DNA biosensors and infrared spectroscopy for rapid and accurate detection of mycotoxin and related fungi is increasing dramatically. Application of new and advanced detection techniques could enable the agricultural industry to deal more effectively with the occurrence of aflatoxin contamination.

Acknowledgments

I would like to thank Dr. Mashilla Dejene from Haramaya University, Department of Plant Pathology for his critical review and comments that he provides to this review article.

References

[1]  Abbas, H. K., Reddy, K. R. N., Salleh, B., Saad, B., Abel, C. A. and Shier, W. T. 2010. An overview of mycotoxin contamination in foods and its implications for human health. Toxin Review 29: 3-26.
In article      CrossRef
 
[2]  Abdulkadar, A. H. W., Al-Ali, A. A., Al-Kildi, A. M. and Al-Jedah, J. H. 2004. Mycotoxins in food products available in Qatar. Food Control 15: 543-548.
In article      CrossRef
 
[3]  Abeywickrama, K. and Bean, G. A. 1991. Toxigenic Aspergillus-Flavus and Aflatoxins in Sri Lankan Medicinal Plant-Material. Mycopathologia 113: 187-190.
In article      CrossRefPubMed
 
[4]  Ali, N., Hashim, N. H., Saad, B., Safan, K., Nakajima, M. and Yoshizawa, T. 2005. Evaluation of a method to determine the natural occurrence of aflatoxins in commercial traditional herbal medicines from Malaysia and Indonesia. Food and Chemical Toxicology 43: 1763-1772.
In article      CrossRefPubMed
 
[5]  Bamba, R. and Sumbali, G. 2005. Co-occurrence of aflatoxin B(1) and cyclopiazonic acid in sour lime (Citrus aurantifolia Swingle) during post-harvest pathogenesis by Aspergillus flavus. Mycopathologia 159: 407-411.
In article      CrossRefPubMed
 
[6]  Bankole, S. A., Adenusi, A. A., Lawal, O. S. and Adesanya, O. O. 2010. Occurrence of aflatoxin B1 in food products derivabl e from 'egusi' melon seeds consumed in southwestern Nigeria. Food Control 21: 974-976.
In article      CrossRef
 
[7]  Bankole, S. A. and Mabekoje, O. O. 2004. Myco flora and occurrence of aflatoxin B-1 in dried yam chips from markets in Ogun and Oyo States, Nigeria. Mycopathologia 157: 111-115.
In article      CrossRefPubMed
 
[8]  Bennett, J. W., 2013. An overview of the genus Aspergillus. PP. 1-17. In: Aspergillus molecular Biology and Genomics. M. Machida and K. Gomi (eds.), Caister Academic Press, Norfolk, UK.
In article      
 
[9]  Bhat, R., Rai, R. V. and Karim, A. A. 2010. Mycotoxins in Food and Feed: Present Status and Future Concerns. Comprehensive Reviews in Food Science and Food Safety 9: 57-81.
In article      CrossRef
 
[10]  Bittencourt, A. B. F., Oliveira, C. A. F., Dilkin, P. and Correa, B. 2005. Mycotoxin occurrence in corn meal and flour traded in Sao Paulo, Brazil. Food Control 16: 117-120.
In article      CrossRef
 
[11]  Blesa, J., Soriano, J. M., Molto, J. C. and Manes, J. 2004. Limited survey for the presence of aflatoxins in foods from local markets and supermarkets in Valencia, Spain. Food Additives and Contaminants 21: 165-171.
In article      CrossRefPubMed
 
[12]  Chun, H. S., Kim, H. J., Ok, H. E., Hwang, J. B. and Chung, D. H. 2007. Determination of aflatoxin levels in nuts and their products consumed in South Korea. Food Chemistry 102: 385-391.
In article      CrossRef
 
[13]  Cornea, C. P., Ciuca, M., Voaides, C., Gagiu, V. and Pop, A. 2011. Incidence of fungal contamination in a Romanian bakery: a molecular approach. Romanian Biotechnological Letters 16: 5863-5871.
In article      
 
[14]  D'Ovidio, K., Trucksess, M., Weaver, C., Horn, E., McIntosh, M. and Bean, G. 2006. Aflatoxins in ginseng roots. Food Additives and Contaminants 23: 174-180.
In article      CrossRefPubMed
 
[15]  Davison, J. 2010. GM plants: Science, politics and EC regulations. Plant Science 178: 94-98.
In article      CrossRef
 
[16]  Elzupir, A. O. and Elhussein, A. M. 2010. Determination of aflatoxin M1 in dairy cattle milk in Khartoum State, Sudan. Food Control 21: 945-946.
In article      CrossRef
 
[17]  Energy., E. C. 2009. The rapid alert system for food and feed (RASFF) Annual report 2008. European Communities.
In article      
 
[18]  Ferracane, R., Tafuri, A., Logieco, A., Galvano, F., Balzano, D. and Ritieni, A. 2007. Simultaneous determination of aflatoxin B<sub>1<sub> and ochratoxin A and their natural occurrence in Mediterranean virgin olive oil. Food Additives and Contaminants 24: 173-180.
In article      CrossRefPubMed
 
[19]  Ghiasian, S. A., Shephard, G. S. and Yazdanpanah, H. 2011. Natural Occurrence of Aflatoxins from Maize in Iran. Mycopathologia 4: 1573-0832.
In article      
 
[20]  Giray, B., Girgin, G., Engin, A. B., Aydin, S. and Sahin, G. 2007. Aflatoxin levels in wheat samples consumed in some regions of Turkey. Food Control 18: 23-29.
In article      CrossRef
 
[21]  Goto, T., Wicklow, D.T. and Ito, Y., 1913. Aflatoxin and cyclopiazonic acid production by a sclerotium-producing Aspergillus tamarii strain. Applied Environmental Microbiology, 62: 4036-4038.
In article      
 
[22]  Gowda, N. K. S., Ledoux, D. R., Rottinghaus, G. E., Bermudez, A. J. and Chen, Y. C. 2008. Efficacy of turmeric (Curcuma longa), containing a known level of curcumin, and a hydrated sodium calcium aluminosilicate to ameliorate the adverse effects of aflatoxin in broiler chicks. Poultry Science 87: 1125-1130.
In article      CrossRefPubMed
 
[23]  Hitokoto, H., Morozumi, S., Wauke, T., Sakai, S. and Kurata, H. 1978. Fungal Contamination and Mycotoxin Detection of Powdered Herbal Drugs. Applied and Environmental Microbiology 36: 252-256.
In article      PubMed
 
[24]  Idris, Y. M. A., Mariod, A. A., Elnour, I. A. and Mohamed, A. A. 2010. Determination of aflatoxin levels in Sudanese edible oils. Food and Chemical Toxicology 48: 2539-2541.
In article      CrossRefPubMed
 
[25]  smail, N., Leong, Y. H., Latif, A. A. and Ahmad, R. 2010. Aflatoxin occurrence in nuts and commercial nutty products in Malaysia. Food Control 21: 334-338.
In article      
 
[26]  Kumar, V., Basu, M. S. and Rajendran, T. P. 2008. Mycotoxin research and mycoflora in some commercially important agricultural commodities. Crop Protection 27: 891-905.
In article      CrossRef
 
[27]  Kumari, N., Kumar, P., Mitra, D., Prasad, B., Tiwary, B. N. and Varshney, L. 2009. Effects of Ionizing Radiation on Microbial Decontamination, Phenolic Contents,and Antioxidant Properties of Triphala. Journal of food science 74: 109-113.
In article      CrossRefPubMed
 
[28]  Lin, Y. L., Wang, T. H., Lee, M. H. and Su, N. W. 2008. Biologically active components and nutraceuticals in the Monascus-fermented rice: a Review. Applied Microbiology and Biotechnology 77: 965-973.
In article      CrossRefPubMed
 
[29]  Macdonald, S. and Castle, L. 1996. A UK retail survey of aflatoxins in herbs and spices and their fate during cooking. Food Additives and Contaminants 13: 121-128.
In article      CrossRefPubMed
 
[30]  Monbaliu, S., Van Poucke, C., Detavernier, C., Dumoulin, F., Van De Velde, M., Schoeters, E., Van Dyck, S., Averkieva, O., Van Peteghem, C. and De Saeger, S. 2010. Occurrence of Mycotoxins in Feed as Analyzed by a Multi-Mycotoxin LC-MS/MS Method. Journal of Agricultural and Food Chemistry 58: 66-71.
In article      CrossRefPubMed
 
[31]  Moss, M. O. 1998. Recent studies of mycotoxins. Symp Ser Soc Appllied Microbiology 27: 62-76.
In article      CrossRef
 
[32]  Nguyen, M. T., Tozovanu, M., Tran, T. L. and Pfohl-Leszkowicz, A. 2007. Occurrence of aflatoxin B1, citrinin and ochratoxin A in rice in five provinces of the central region of Vietnam. Food Chemistry 105: 42-47.
In article      CrossRef
 
[33]  Njobeh, P. B., Dutton, M. F., Koch, S. H., Chuturgoon, A., Stoev, S. and Seifert, K. 2009. Contamination with storage fungi of human food from Cameroon. International Journal of Food Microbiology 135: 193-198.
In article      CrossRefPubMed
 
[34]  Odoemelam, S. A. and Osu, C. I. 2009. Aflatoxin B(1) Contamination of Some Edible Grains Marketed in Nigeria. E-Journal of Chemistry 6: 308-314.
In article      CrossRef
 
[35]  Oliveira, C. A. F., Sebastiao, L. S., Fagundes, H., Rosim, R. E. and Fernandes, A. M. 2008. Aflatoxins and cyclopiazonic acid in feed and milk from dairy farms in Sao Paulo, Brazil. Food Additives and Contaminants Part B-Surveillance 1: 147-152.
In article      CrossRefPubMed
 
[36]  Patel, S., Hazel, C. M., Winterton, A. G. M. and Mortby, E. 1996. Survey of ethnic foods for mycotoxins. Food Additives and Contaminants 13: 833-841.
In article      CrossRefPubMed
 
[37]  Pharmacopeia, E. 2007. Determination of aflatoxin B1 in herbal drugs. In European Pharmacopeia (6 ed.). Strasbourg Directorate for the Quality of Medicines and HealthCare of the Council of Europe (EDQM).
In article      
 
[38]  RASFF. 2011. RASFF portal. In DG SANCO https://webgate.ec.europa.eu/rasff window/portal/.
In article      
 
[39]  Rivka, N. P. 2008. Mycotoxins in fruits and vegetables. In: Burlington Academic Press, 978-0-12-374126-4.
In article      
 
[40]  Roige, M. B., Aranguren, S. M., Riccio, M. B., Pereyra, S., Soraci, A. L. and Tapia, M. O. 2009. Mota and mycotoxins in fermented feed, wheat grains and corn grains in Southeastern Buenos Aires Province, Argentinaycobi. Revista Iberoamericana De Micologia 26: 233-237.
In article      CrossRefPubMed
 
[41]  Romagnoli, B., Menna, V., Gruppioni, N. and Bergamini, C. 2007. Aflatoxins in spices, aromatic herbs, herb-teas and medi cinal plants marketed in Italy. Food Control 18: 697-701.
In article      CrossRef
 
[42]  Roy, A. K., Sinha, K. K. and Chourasia, H. K. 1988. Aflatoxin Contamination of Some Common-Drug Plants. Applied and Environmental Microbiology 54: 842-843.
In article      PubMed
 
[43]  Rustemeyer, S. M., Lamberson, W. R., Ledoux, D. R., Rottinghaus, G. E., Shaw, D. P., Cockrum, R. R., Kessler, K. L., Austin, K. J. and Cammack, K. M. 2010. Effects of dietary aflatoxin on the health and performance of growing barrows. Journal of Animal Science 88: 3624-3630.
In article      CrossRefPubMed
 
[44]  Rustom, I. Y. S. 1997. Aflatoxin in food and feed: Occurrence, legislation and inactivation by physical methods. Food Chemistry 59: 57-67.
In article      CrossRef
 
[45]  Scheidegger, K.A. and Payne, G.A., 2012. Unlocking the secrets behind secondary metabolism: A review of Aspergillus flavus from pathogenicity to functional genomics. Journal of Toxicology, 22: 423-459.
In article      
 
[46]  Seo, J. H., Min, W. K., Kweon, D. H., Park, K. and Park, Y. C. 2011. Characterisation of monoclonal antibody against aflatoxin B(1) produced in hybridoma 2C12 and its single-chain variable fragment expressed in recombinant Escherichia coli. Food Chemistry 126: 1316-1323.
In article      CrossRef
 
[47]  Set, E. and Erkmen, O. 2010. The aflatoxin contamination of ground red pepper and pistachio nuts sold in Turkey. Food Chemistry and Toxicology 48: 2532-2537.
In article      CrossRefPubMed
 
[48]  Sewram, V., Shephard, G. S., van der Merw e, L. and Jacobs, T. V. 2006. Mycotoxin contamination of dietary and medicinal wild plants in the Eastern Cape Province of South Africa. Journal of Agricultural and Food Chemistry 54: 5688-5693.
In article      CrossRefPubMed
 
[49]  Smiley, R. D. and Draughon, F. A. 2000. Preliminary evidence that degradation of aflatoxin B1 by Flavobacterium aurantiacum is enzymatic. Journal of Food Protection 63: 415-418.
In article      PubMed
 
[50]  Smith, J. E. and Moss, M. O. 1985. Mycotoxins. Formation, analysis and significance. John Wiley and Sons Ltd.,ISBN 0-471-90671-9, Chichester.
In article      
 
[51]  Tassaneeyakul, W., Razzazi-Fazeli, E., Porasuphatana, S. and Bohm, J. 2004. Contamination of aflatoxins in herbal medicinal products in Thailand. Mycopathologia 158: 239-244.
In article      CrossRefPubMed
 
[52]  Trucksess, M. W. and Scott, P. M. 2008. Mycotoxins in botanicals and dried fruits: A review. Food Additives and Contaminants 25: 181-192.
In article      CrossRefPubMed
 
[53]  Umoh, N. J., Lesi, O. A., Mendy, M., Bah, E., Akano, A., Whittle, H., Hainaut, P. and Kirk, G. D. 2011. Aetiological differences in demographical, clinical and pathological characteristics of hepatocellular carcinoma in The Gambia. Liver International 31: 215-221.
In article      CrossRefPubMed
 
[54]  Vargas, E. A., Preis, R. A., Castro, L. and Silva, C. M. 2001. Co-occurrence of aflatoxins B1, B2, G1, G2, zearalenone and fumonisin B1 in Brazilian corn. Food Additive Contaminants 18: 981-986.
In article      CrossRefPubMed
 
[55]  Vasanthi S, B. R. 1998. Mycotoxins in foods --occurrence, health & economic significance & food control measures. Indian Journal of Medical Researches 108: 212-224.
In article      PubMed
 
[56]  Yang, M.-H., Chen, J.-M. and Zhang, X.-H. 2005. Immunoaffinity Column Clean-Up and Liquid Chromatography with Post-Column Derivatization for Analysis of Aflatoxins in Traditional Chinese Medicine. Chromatographia 62: 499-504.
In article      CrossRef
 
[57]  Yazdanpanah, H. 2006. Mycotoxin Contamination of Foodstuffs and Feedstuffs in Iran. Iranian Journal of Pharmaceutical Research 1: 9-16.
In article      
 
[58]  Yu, J., Cleveland, T.E., Nierman, W.C. and Bennett, J.W., 2012. Aspergillus flavus genomics: Gateway to human and animal health, food safety, and crop resistance to diseases. Revista Iberoamericana de Micología, 22: 194-202.
In article      CrossRef
 
[59]  Zinedine, A., Brera, C., Elakhdari, S., Catano, C., Debegnach, F., Angelini, S., De Santis, B., Faid, M., Benlemlih, M., Minardi, V. and Miraglia, M. 2006. Natural occurrence of mycotoxins in cereals and spices commercialized in Morocco. Food Control 17: 868-874.
In article      CrossRef
 
  • CiteULikeCiteULike
  • MendeleyMendeley
  • StumbleUponStumbleUpon
  • Add to DeliciousDelicious
  • FacebookFacebook
  • TwitterTwitter
  • LinkedInLinkedIn