NASAM FAQ

Aflatoxins are chemicals produced by moulds called Aspergillusflavus and Aspergillusparasiticus. Aflatoxins are difuranocoumarin derivatives synthesized by a polyketide pathway by many strains of these moulds.A. flavus is a common contaminant in agriculture. Other fungus such as A. bombycis, A. ochraceus, A. nomius, and A. pseudotamari are also aflatoxin-producing species, but they are encountered less frequently in agricultural produce. There are great qualitative and quantitative differences in the aflatoxin-producing abilities displayed by different isolates of each aflatoxigenic species.

Aflatoxins occur in several chemical forms, designated aflatoxin B1, B2, G1, and G2. “B” and “G” refer to the blue or green fluorescence observed with exposure of the toxin to ultraviolet irradiation. M1 is the predominant metabolite of AFB1 in milk from lactating humans and animals that consume AFB1-contaminated food or feed.

According to the IARC, there is sufficient evidence to conclude that AFB1 and mixtures of B1, G1, and M1 are proven human carcinogens, thereby warranting Group 1 carcinogen status for them. M1 and B2 are designated as Group 2B probable human carcinogens.

The moulds are naturally found in the air, soil, on insects and plants and grow on crops and grains and produce aflatoxins to contaminate these crops.Generally, AF contamination can occur at both pre-and post-harvest stages of food production. Poor agricultural practices during planting, insect damage, drought, harvesting, drying, transportation and storage are predisposing factors. The moulds have 2 stages which are the saprophytic and pathogenic stages. The saprophytic stage mainly occurs in the soil and plant residue which produces conidia which are carried by wind or insect onto the plant and then the pathogenic stage begins.

Aflatoxins can affect the human DNA and also cause cancer. Like the hepatitis B virus, aflatoxin B1 is recognized by the International Agency for Research on Cancers as a major risk factor for liver cancer. It can suppress the immune system therefore not good for HIV patients. It leads to stunted growth.

This usually occurs when AFB1 is metabolized by the liver by the cytochrome P450 enzyme system to the major carcinogenic metabolite AFB1-8, 9-epoxide (AFBO), or to other less mutagenic forms such as AFM1, Q1, or P1. The exo-form of AFBO readily binds to cellular macromolecules to form adducts. The macromolecules include proteins and DNA. It is the formation of DNA adducts, such as with N7-guanine, that leads to gene mutations and cancer.

The AFB1-N7-guanine adduct is excreted in the urine of those affected. Urinary excretion not only serves as evidence that humans have the necessary biochemical pathways for carcinogenesis, but also provides a reliable biomarker for exposure to AFB1.

A grain containing toxin-producing moulds can be difficult or impossible to recognize because it may not appear overtly mouldy. Even when visibly mouldy you cannot see aflatoxins in the grain with your naked eye. Techniques to detect and quantify aflatoxins important to domestic animal and human health are available through diagnostic laboratories.

Aflatoxin formation was assumed to occur only during postharvest period, that is, during storage, however, it has now been proven that aflatoxin formation can also occur in the field even before harvest.  The most important factors that help predict the occurrence of aflatoxins in food include weather conditions (temperature and atmospheric humidity), agronomical practices (crop rotation and soil cultivation) and internal factors of the food chain (drying and storage conditions).  Based on numerous researches, aflatoxin formation has been found to occur in three basic stages in the food production chain.

• For the cultivation stage, the selected indicators are relative humidity, temperature, crop rotation, tillage practices and water activity of seeds.
• For transportation and storage stage, the following factors are included: water activity, relative humidity, ventilation, temperature, storage capacity and logistics.
• For the processing stage, the indicators are data quality, the fraction on of grain used, the water activity of seeds, implanted traceability and system quality.

Aflatoxin contamination has been attributed to prolonged high day and night temperatures during the growing season and severe drought conditions during grain fill.  Risk factors for aflatoxin contamination include three or more weeks drought during pod formation (end of season drought), high moisture/relative humidity (83+1% or higher at 30 ⁰C varying with substrate and length of incubation period) and high temperature with optimum temperatures between 25-35 ⁰C.or more, rainfall at the end of the growing season that postpones harvest and prevents dry-down.  In terms of storage conditions, grains with moisture levels above 9% and moderate temperatures (28 ⁰C to 33 ⁰C) increase the risk of aflatoxin contamination, and grain damage by insects, rodents, birds, as well as drought stress predisposes the crop to colonization by fungi.

Aflatoxins causes liver necrosis, liver tumors, reduced growth, depressed immune response and carcinogenesis.When exposed to very high levels of aflatoxins it can be fatal. Chronic exposure to low levels can lead to liver cancer and cause suppression of the Immune system.

When aflatoxins are consumed by a person with Hepatitis B or HIV aflatoxins facilitate liver cirrhosis and imunosuppression.Simultaneous AFB1 and hepatitis B infections commonly occur in regions with high rates of hepatocellular carcinoma (HCC).

A cohort study of more than 18,000 individuals in China clearly showed a relative risk for HCC of 3.4 in subjects with AFB1 exposure (urinary AFB1-N7-guanine), whereas relative risk for subjects positive for hepatitis B antigen was 7.3. Combination of hepatitis B and AFB1 exposure increased relative risk for HCC to 59 (Qian et al., 1994). Thus, AFB1 is an independent and possibly strongly potentiating factor for human HCC.

The incidence of primary liver carcinoma is unusually high in some African and Asian regions. The role of aflatoxins in the development of the primary liver carcinoma, irrespective of the hepatitis B virus, was confirmed in investigations performed in China and Switzerland (Peers et al., 1987).

It is also responsible for childhood stunting with some linkage to kwashiokor. It is estimated that around 30% of all liver cancers worldwide could be related to aflatoxins exposure. In livestock, aflatoxins can cause weight loss and death. Milk, meat or eggs obtained from animals fed with contaminated food may contain aflatoxins.

Aflatoxins contamination contribute to nutritional and economic losses in major commodities including but not limited to maize, groundnuts, sorghum, cassava, melon seeds (agushie), spices, dried fruits etc.

Products prepared from contaminated raw materials also do not meet international, regional, national regulations and standards governing agricultural or food trade and food safety.

Small scale farmers are mainly at the losing end since these contaminated crops do not meet food safety standards hence undermines local purchase programs by development partners and therefore accessibility to other markets are blocked.

Exporters are faced with rejects from border controls of importing countries when aflatoxin levels determined in pre-packed foods or raw materials exceed allowable limits of these countries.

Aflatoxins cannot be prevented or eliminated by current agricultural practices because they are considered unavoidable contaminants of food. There should be strategies and methods put in place to reduce the level of contamination. Blanching and electronic eye color sorting may be a strategy to reduce the concentration of total aflatoxinsin peanuts.

In high temperatures, A. flavus and F. moniliforme are widely distributed in nature. Usually within temperatures ranging from 27 to 38 degrees and a relative humidity of 85 percent corresponding to 18 to 20 percent moisture in the grain are optimum for fungal growth and toxin production. However at moisture of 12 to 13 percent these fungi do not grow.

The following practices can help minimize the level of aflatoxins in agricultural produce.

• Use of recommended crop production practices
• Planting early

• irrigation of plants to reduce drought stress,
• minimization of insect damage,
• harvesting early,
• avoiding produce damage during harvest,
• drying and storing produce properly and
• Keeping storage facilities clean.

Aflatoxins may contaminate many crops including peanuts (groundnuts), rice, corn (maize), cottonseed, Brazil nuts, spices, and figs. Widespread contamination occurs in the in hot and humid regions of the world.

• Aflatoxins may be present in foods such as treenuts, peanuts, corn/maize, rice, dried fruits, spices, raw vegetable oils, and cocoa beans with fungal contamination before and after harvest.
• In Ghana, the presence of aflatoxins has been detected in peanut,maize, melon seeds (agushie), chili powder, corn meals, rice, tom brown, hausakoko, sorghum, groundnuts, groundnut paste etc.

Aflatoxin M1 is as important and may be present in milk from animals fed with food contaminated by aflatoxin B1.