Several studies have been conducted in Nigeria on aflatoxins in foods. A two-year countrywide survey was initiated in Nigeria in 1980 to determine storage losses of food crops at the market level (Opadokun and Ikeorah, 1983). During the study, 145 maize samples from markets in Kano and Plateau States of Nigeria were assayed for moisture and aflatoxin content.
Over 20% (30 samples) had detectable aflatoxin Bi (> 5 ng/g). Twenty-one samples had aflatox-in Bi levels > 30 ng/g and one sample contained 1,300 ng/g of aflatoxin Bi. Various human foods and feeds also were screened for aflatoxins and 9/22 maize samples were positive for afla-toxins with a mean level of 21 ng/g and a range of 20-110 ng/g (Atawodi et al, 1994).
Moldy maize samples from Plateau State contained aflatoxins, zearalenone and ochra-toxin A. An aflatoxin level of 960 ng/g was obtained for a sample from Langtang (Gbodi et al., 1986). Of 48 samples of maize-based gruels used as weaning food for children admitted to the Wesley Guild Hospital in Ilesha, 12 were positive for aflatoxins with levels up to 20 ng/g (Oyelami et al., 1996).
In other studies, 80% of maize samples from different locations in southeastern Nigeria were positive for aflatoxin B1 (Aja-Nwachukwu and Emejuaiwe, 1994). In southwestern Nigeria, 45% of raw maize from farms, 80% of maize cakes and 12% of maize rolls were contaminated with aflatoxins at mean levels of 200, 233, and 55 ng/g, respectively (Adebajo et al, 1994).
The agroecological zones in which maize was grown affected the amount of aflatoxin present, as did the storage method. The highest level of contamination, 3,100 ng/g, was obtained from the Humid Forest zone while the lowest aflatoxin content, 670 ng/g, was obtained from the Southern Guinea Savanna zone. No aflatoxins were detected in maize samples from the Northern Guinea Savanna zone (Udoh, 1997). Storage of maize in bags and "rhumbu" (traditional clay stores) was correlated with lower aflatoxin levels in the Sudan Savanna region of Nigeria (Udoh, 1997). Similar regional studies have been conducted on other commodities and products from the savanna and forest regions (Nwokolo and Okonkwo, 1978). High risk foods (> 200 ng/g of aflatoxin B1) included peanuts, dried fish, guinea corn (sorghum) and millet. Maize, rice, beans, and crude palm-oil contained 30-200 ng/g of aflatoxin B1. Low risk foods (< 30 ng/g) included cereal "acha" ("findi"), some cassava products, yams and refined vegetable oils. Confirmation of peanuts as a food at high risk for mycotoxin contamination was obtained from studies conducted by several researchers (Akano and Atanda, 1990; Atawodi et al., 1994). Eighty-seven percent of peanut cake ("Kulikuli") samples purchased from markets in Ibadan contained aflatoxin B1. Levels ranged from 20-460 ng/g. In other studies (Atawodi et al, 1994), levels as high as 1,900 ng/g were observed in peanut cake samples whilst 64% of 106 roasted peanut samples from retail outlets in Nigeria contained aflatoxin B1 with a mean value of 25 ng/g.
Aflatoxins were detected in 18/100 samples of foods - "gari", yam flour, cassava flour, melon, onion, rice, plantain, red pepper and eggs - from Benin City (Ibeh et al., 1991). Af-latoxins also were detected in five samples of yam flour, four samples of cassava flour, three samples of "gari", two samples each of beans and melon, and one sample of rice. Extremely high concentrations of aflatoxins were recorded in yam flour (4,000-7,600 ng/g). Cassava flour also contained high levels of aflatoxins ranging from 3,500-5,400 ng/g. Pepper, onion, plantain and eggs did not contain detectable amounts of aflatoxins.
In another study, aflatoxins were detected in melon seed and tiger nut (Cyperus escu-lentus) samples. Aflatoxin B1 was detected in 32% of melon seed samples collected from Nigerian markets, with the means of 14 and 11 ng/g, respectively, for samples from the forest and savanna zones (Bankole et al., 2004). The presence of aflatoxins in 35% of the tiger nut samples obtained from different parts of Nigeria at levels ranging from 10-120 ng/g also has been reported (Bankole and Eseigbe, 1996). Fifty-four percent of dried yam chips for sale in various parts of western Nigeria were contaminated with aflatoxin B1 at levels of 4190 ng/g (mean 23 ng/g), and 32% with aflatoxin B2 (2-55 ng/g). Five percent of the sam ples contained aflatoxin Gi (4-18 ng/g) with two samples testing positive for aflatoxin G2 (Bankole and Adebanjo, 2003).
Aflatoxins have been detected in Nigerian indigenous beverages (Alozie et al., 1980; Okoye and Ekpenyong, 1984). In the Jos metropolis aflatoxin B1 contamination was common in the traditionally brewed millet-based beers "pito" and "burukutu" (Okoye and Ekpenyong, 1984). Seventeen of 20 "pito" samples contained aflatoxin at levels ranging from 16-140 ng/g while 15/20 "burukutu" samples contained aflatoxins at levels ranging from 1.7 to 140 ng/g. In this study the millet raw material was not analyzed for aflatoxins.
In another survey (Alozie et al., 1980), 16 Nigerian indigenous beverages and foodstuffs, all eight beverage samples from Ugbowo in Benin City were contaminated with aflatoxins. The beverages were "burukutu", "pito", "emu aran" (fermentable sap of the Raphia palm; R. vinifera and R. raphia), and "ogoro" (fermentable sap of immature shoots of the oil palm, Elais guinensis). Aflatoxin levels ranged from 83 ng/g in "emu aran" to 260 ng/g in "burukutu". Foodstuffs evaluated in this study also were purchased from markets in Benin City and included "gari" (Cassava farina), "ogbono" (Irvingia gabunesis), "egusi" meal (Cucumeropsis edulis), "ogili-ugba" (prepared from castor bean, Riccinus communis), "dawadawa" (prepared from locust bean, Parkia filicoden), "ewedu" (Coconus seratus) and "shoko yokoto" (Ceropsia sp.). All the foodstuffs except "dawadawa", "ewedu", and "shoko yokoto" contained aflatoxins (Alozie et al., 1980).
In Senegal high levels of aflatoxins were found in peanut cake and unrefined oil, with > 90% of market samples of unrefined oil contaminated with > 300 ng/g of aflatoxins (Clavel, 1995). In peanut oil foods in Kaolack and Diourbel, > 85% of the samples were contaminated with aflatoxin B1 at a mean of 40 ng/g (Ndiaye et al., 1999). The mean level of total aflatoxin in peanut oil from small-scale units in two regions of Senegal ranged from 57-82 ng/g (Diop et al., 2000).
There are few studies of aflatoxin contamination in Sierra Leone. Twenty samples of Bon-ga, a smoke-dried fish, obtained from homes and markets in Njala were contaminated with four Aspergillus spp. - A. flavus, A. ochraceus, A. tamarii and A. niger. Varying amounts of aflatoxins B1, G1 and G2 were detected in the moldy fish (Jonsyn, 1992). Aflatoxins also were reported in fermented sesame seeds (Jonsyn, 1990).
Central African countries
No reports were available of aflatoxins in foods in any Central African country. Fumonisins
Fumonisins are mycotoxins produced by Fusarium verticillioides, formerly termed F. mo-niliforme (Seifert et al., 2003), and Fusarium proliferatum which are among the fungi most commonly associated with maize. These toxins normally are synthesized before harvest or during the early stages of drying, and, except under unusual conditions, do not increase during grain storage (Fandohan et al., 2005). Since the discovery of fumonisins in 1988 (Gel-derblom et al., 1988), these toxins have been found as natural contaminants of maize and maize-based foods and feeds in many parts of the world
Fumonisins have been associated with a high incidence of esophageal cancer in certain areas of the Transkei region of the Eastern Cape Province in South Africa (van Rensburg, 1985; Rheeder et al, 1992) and high levels of fumonisin levels have been found in maize from this and other parts of the world known to have unusually high rates of esophageal cancer such as the Linxian county region in China (Yang, 1980), northeastern Iran (Kmet and Mahboubi, 1972; Shephard et al., 2000), northeastern Italy (Franceschi et al., 1990). Fumonisins also may be a risk factor in primary liver cancer and could act synergistically with aflatoxins, microcystins and/or deoxynivalenol (Ueno et al., 1996).
Whether fumonisin Bi is a carcinogen in human beings has not been established; however, based on toxicological evidence, the International Agency for Research on Cancer (IARC) has designated fumonisin B1 to be possibly carcinogenic to humans (class 2B carcinogen) (IARC, 2002). The development of neural tube defects in rural populations known to consume contaminated maize has been related to the inhibition of uptake of folic acid by fumonisins and, although not yet confirmed, fumonisins are believed to play a critical role in the disruption of folate membrane transport (WHO, 2002).
Limited surveys of good-quality maize from hybrids grown in Benin in 1992 found that 82% of the samples contained fumonisins at levels up to 3,300 ng/g. The mean fumonisin level for the positive samples was 700 ng/g (Doko et al., 1995). In a more recent study in Benin, widespread fumonisin occurrence in maize also was reported. Samples from the 1999-2000 crop year contained fumonisins at up to 12,000 ng/g. For the 2000-2001 crop year, fumonisin levels were as high as 6,700 ng/g, and as high as 6,100 ng/g for the 20022003 crop year (Fandohan et al., 2005).
Maize from Burkina Faso, Ghana, Nigeria and Cameroon also are contaminated with fumonisins (Kpodo et al., 2000; Bankole et al., 2003; Nikiema et al., 2004). In Burkina Faso, 72 market samples of maize contained fumonisins at levels ranging from 130-16,000 ng/g, as did 52 samples obtained from farms with fumonisins present at between 10 and 3,100 ng/g (Nikiema et al., 2004). In Ghana, 14 maize samples contained between 70 and 4,200 ng/g of fumonisins with eight samples co-contaminated with aflatoxins (Kpodo et al., 2000). In another study from Ghana, 68/75 maize samples from different sites contained fumonisins at levels ranging from 11-2,500 ng/g, while 55/75 kenkey samples contained fumonisins at levels of 15-1,000 ng/g (Kpodo, 2001). In one study from Nigeria, 55/108 maize samples were positive for fumonisin B1 with levels ranging from 65 to 1,800 ng/g with a mean value of 390 ng/g for the positive samples (Bankole et al., 2003). Studies in the Cameroon (Ngoko et al, 2001) identified fumonisins in 13/15 maize samples at levels ranging from 300-26,000 ng/g.
The only report of fumonisin contamination of foods in Central Africa was a study conducted in Burundi on 50 food samples by Munimbazi and Bullerman (1996). Fumonisin B1 was detected in six maize samples at levels ranging from 12-75 ng/g. In the same study, fumonisin B1 was detected in one sorghum meal sample.
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