Questions and answers about aflatoxins
Where do the aflatoxins come from?
Aflatoxins are fungal secondary metabolites produced by Aspergillus flavus and Aspergillus parasiticus. These fungi are found in the natural environment, and are easily isolated from plants, soil, air and some insects. When they colonize crops or grain they produce aflatoxins sufficiently to contaminate these materials.
There are several types of aflatoxins which differ slightly from each other according to their chemical structure. Aflatoxins B1, B2, G1 and G2 are found in foods. Aflatoxins M1 and M2, are hydroxyl derivatives of B1 and B2 aflatoxins, they can be detected in milk respectively.
Among other properties, aflatoxins have a genetoxic and carcinogenic property. Aflatoxins B1 is the most abundant and also the most toxic one. 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 is one of the most powerful carcinogenic agents of natural origin that we know. Aflatoxin M1 is a potential carcinogenic agent.
Which foods are most likely to be contaminated by aflatoxins ?
Aflatoxins may be present in foods such as nuts, peanuts, corn, rice, banana and other dry foods, spices, raw vegetable oils, and cocoa beans with fungal contamination before and after harvest. In Haïti, the presence of aflatoxins has been detected in peanut and its byproducts, including peanut butter as well as corn and sorghum.
Aflatoxin M1 is an important metabolite of aflatoxin B1 in human and animal; it may be present in milk from animals fed with food contaminated by aflatoxin B1.
Which regions are most affected?
Aspergillus that produce aflatoxins grow best in warm and humid tropical areas. They have been found in foods from different regions of Haiti.
At what stage of the food chain does aflatoxin occur?
Aspergillus fungi can grow and produce aflatoxins at all stages of food production, processing, distribution and marketing because the conditions are favorable for their multiplication. Warm temperatures and high humidity levels facilitate their multiplication.
Aflatoxins contamination can occur at any time, from farm to table. They do not change the appearance or taste of the food and therefore they remain undetectable. They are not destroyed by cooking process or fermentation.
What are the effects of aflatoxins health?
If exposure to very high levels of aflatoxins can be fatal, chronic exposure to low levels can lead to liver cancer and cause immunosuppression. It is also responsible for childhood stunting. 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.
How can we measure a population exposure to aflatoxins ?
It is possible to estimate the exposure level of a population to aflatoxins by determining the contamination level of food samples and correlating the collected data with the results of nutritional surveys. Some techniques provide more specific indicators such as biomarkers, which are objective indicators of a person's exposure level. The biomarkers use mostly aflatoxin-N7-guanine adducts present in urine which shows exposure from the last day, the hydroxylated metabolite of aflatoxin B1 or aflatoxin M1, present in milk which reflects the exposure from the last 24 hours, and the adduct of aflatoxin and albumin present in the blood serum. The half life of this latter biomarker is aproximately 2 months, which allows the evaluation of chronic exposure to aflatoxins.
How to prevent food contamination by aflatoxins?
Several precautions can be taken, either before harvest or after harvest to reduce peanut, corn and other crops aflatoxins levels. The biotic and abiotic stresses to which crops are exposed can be reduced, for example by ensuring good irrigation and effective control of disease and pests. It is also important to harvest at the right time and to ensure proper management of crops residues. Biological control can also be used, for example using Aspergillus strains that do not produce aflatoxins can compete with the producing strains and thus limit their colonization capacity. On the other hand, some plant varieties may be less favorable to fungi colonization than others.
Postharvest strategies involve adequate drying, followed by proper storage in sealed bags that protect the grains against fungal contamination. Grains should be stored in clean, dry warehouses, protected from insects. The sorting of contaminated, discolored or damaged grains is also an effective way to prevent aflatoxins contamination of foods.