Aflatoxins

Aflatoxins are a group of highly toxic and carcinogenic compounds produced by certain species of fungi belonging to the genus Aspergillus, particularly Aspergillus flavus and Aspergillus parasiticus. These naturally occurring mycotoxins contaminate a wide range of agricultural commodities, especially cereals, nuts, and oilseeds, posing serious threats to food safety, animal health, and human wellbeing.

Chemical Nature and Types

Aflatoxins are secondary metabolites, meaning they are not essential for the fungi’s growth but are produced under specific environmental conditions, particularly warm and humid climates. They belong to the difuranocoumarin class of compounds and exhibit high stability against normal food processing methods such as cooking and boiling.
There are more than a dozen known aflatoxins, but the most significant in terms of toxicity and occurrence are:

• Aflatoxin B₁ – The most potent and prevalent; known human carcinogen.
• Aflatoxin B₂ – A less toxic derivative of B₁.
• Aflatoxin G₁ and G₂ – Produced mainly by A. parasiticus.
• Aflatoxin M₁ and M₂ – Hydroxylated metabolites of B₁ and B₂, found in milk and dairy products of animals that consume contaminated feed.

The designations “B” and “G” refer to the blue and green fluorescence they emit under ultraviolet light, a property used for detection.

Sources and Conditions of Formation

Aflatoxins develop when Aspergillus fungi infect crops during pre-harvest growth or post-harvest storage under favourable environmental conditions. Factors contributing to contamination include:

• High humidity (above 70%) and temperatures between 25°C and 35°C.
• Poor storage conditions, including inadequate drying, high moisture, and insect infestation.
• Drought stress or plant damage that weakens crops, allowing fungal invasion.

Commonly affected commodities include:

• Cereals – maize, rice, wheat, sorghum, barley.
• Nuts – peanuts, pistachios, almonds, and walnuts.
• Oilseeds – soybeans, cottonseed, and sunflower seeds.
• Spices and dried fruits – chilli, black pepper, and figs.

In tropical and subtropical regions, where warm and moist conditions prevail, aflatoxin contamination is a persistent agricultural and public health concern.

Mechanism of Toxicity

Aflatoxins are potent hepatotoxins and carcinogens, with Aflatoxin B₁ being the most toxic. Once ingested, it is metabolised by the liver’s cytochrome P450 enzymes into a reactive epoxide form, which binds to DNA and proteins, causing mutations and cellular damage.
Key toxic effects include:

• Acute aflatoxicosis: A rapid and severe form of poisoning characterised by liver necrosis, jaundice, abdominal pain, and potentially death.
• Chronic toxicity: Long-term exposure leads to liver cancer (hepatocellular carcinoma), immune suppression, and growth retardation.
• Synergism with hepatitis B virus: Individuals infected with the hepatitis B virus face a significantly increased risk of liver cancer when exposed to aflatoxins.

The International Agency for Research on Cancer (IARC) classifies Aflatoxin B₁ as Group 1 – Carcinogenic to humans.

Impact on Animals

Livestock consuming contaminated feed may suffer from reduced productivity, impaired growth, and reproductive disorders. Dairy cattle excrete the metabolite Aflatoxin M₁ in milk, leading to human exposure through dairy products. Poultry and pigs are particularly susceptible, experiencing decreased egg production and feed efficiency.
Regulatory agencies set strict limits for permissible aflatoxin levels in animal feed to prevent carry-over into the food chain.

Detection and Analysis

Various analytical and screening techniques are employed for detecting aflatoxins in food and feed:

• Fluorescence detection under UV light after thin-layer chromatography (TLC).
• High-Performance Liquid Chromatography (HPLC) with fluorescence or mass spectrometry detectors for quantitative analysis.
• Enzyme-Linked Immunosorbent Assay (ELISA) for rapid field-level screening.
• LC-MS/MS (Liquid Chromatography–Tandem Mass Spectrometry) for highly sensitive multi-toxin detection.

Advances in biosensors and immunoassays have improved the speed and sensitivity of aflatoxin monitoring.

Prevention and Control Strategies

Effective control of aflatoxin contamination requires interventions at multiple stages — from crop production to storage and processing.
1. Pre-Harvest Management:

• Use of resistant crop varieties and biocontrol agents such as Aspergillus flavus strains that do not produce aflatoxins (e.g., Aflasafe).
• Crop rotation and proper irrigation to minimise plant stress.
• Timely harvesting to avoid fungal colonisation during prolonged field exposure.

2. Post-Harvest Practices:

• Proper drying of grains and nuts to moisture levels below 10–12%.
• Airtight storage in cool, dry environments to inhibit fungal growth.
• Regular inspection and sorting to remove damaged or mouldy grains.
• Application of natural antifungal agents, such as plant extracts or organic acids.

3. Processing and Detoxification: Although aflatoxins are heat-stable, certain processes can reduce their levels:

• Ammoniation and ozonation of contaminated feed.
• Use of adsorbent materials such as bentonite or activated charcoal in animal feeds to bind toxins.
• Nixtamalisation (alkaline cooking of maize) reduces aflatoxin levels through chemical breakdown.

4. Regulatory Measures: Many countries have established maximum permissible limits for aflatoxins in food and feed.

• The European Union typically enforces limits as low as 2 µg/kg for Aflatoxin B₁ in foodstuffs.
• The United States Food and Drug Administration (FDA) sets an upper limit of 20 µg/kg total aflatoxins for most food products.Continuous surveillance and food safety monitoring programmes are essential to maintain compliance.

Public Health and Socioeconomic Impact

Aflatoxin contamination has wide-ranging health and economic repercussions:

• Public health: Chronic exposure contributes to liver disease, stunted growth in children, and immune system impairment.
• Food security: Contaminated crops result in significant post-harvest losses and export rejections.
• Economic costs: Developing countries in Africa and Asia face substantial losses due to trade restrictions and reduced market access.

Efforts to mitigate aflatoxin exposure form a key component of global food safety initiatives, particularly under the World Health Organization (WHO) and the Food and Agriculture Organization (FAO).

Research and Innovation

Recent research focuses on biotechnological and molecular approaches to prevent aflatoxin contamination, including:

• Genetic engineering of crops for fungal resistance.
• Development of biocontrol organisms that outcompete aflatoxigenic fungi.
• Application of RNA interference (RNAi) to suppress toxin biosynthesis genes in Aspergillus.
• Use of remote sensing and predictive modelling to forecast contamination risks based on climatic data.

Public awareness campaigns and community-based monitoring programmes also play an important role in controlling aflatoxin exposure at the household level.

Global Distribution and Risk Zones

Aflatoxin contamination is most prevalent in tropical and subtropical regions, including parts of Africa, South and Southeast Asia, and Latin America, where warm and humid conditions favour fungal proliferation. Climate change, with its influence on temperature and rainfall patterns, is expected to expand the geographical range of aflatoxin risk zones.