Food Safety Focus (153rd Issue, April 2019) – Food Safety Platform

Aflatoxins: The Most Notorious Mycotoxins

Reported by Ms. Janny MA, Scientific Officer,
Risk Assessment Section, Centre for Food Safety

Mycotoxins are a group of naturally occurring toxic compounds produced by certain moulds (fungi).  Currently, hundreds of different mycotoxins have been identified; only few of them have been associated with potential toxicity to animals and humans.  Let's kick off this mycotoxin series with the most poisonous ones – aflatoxins.

Aflatoxins in Food

Aflatoxins are a family of heat-resistant compounds produced by the moulds Aspergillus flavus, Aspergillus parasiticus and related species, which are especially abundant in hot and humid areas.  Among the 14 or more aflatoxins identified, aflatoxins B₁, B₂, G₁ and G₂ are of particular health concern in both humans and animals.  In general, of these four aflatoxins, aflatoxin B₁ is the most frequently present in contaminated food; aflatoxin B₂, G₁ and G₂ are usually not reported in the absence of aflatoxin B₁.

(a) Mouldy peanut and (b) mouldy peanut under UV light with fluorescence observed

Fun Facts about Aflatoxins

• The term “aflatoxin” was derived from the mould, Aspergillus flavus that produced it i.e. a toxin.
• Aflatoxins are readily detected by a strong fluorescence in UV light; aflatoxins B₁ and B₂ produce blue fluorescence while aflatoxins G₁ and G₂ produce green fluorescence.
• The subscript numbers ₁ and ₂ indicate major and minor compounds respectively.
• Aflatoxin M₁ is the metabolite of aflatoxin B₁ that can occur in milk and milk products (hence the designation M) from animals consuming contaminated feed.

Food commodities such as cereals (e.g. maize, wheat and rice), oilseeds (e.g. peanut) and tree nuts (e.g. pistachio and almond) are susceptible to aflatoxin contamination.

Adverse Health Effects in Humans

Ingesting large doses of aflatoxins can result in acute poisoning, i.e. aflatoxicosis, which could be deadly, usually through damage to the liver.  

Long-term consumption of food contaminated with aflatoxins can also result in adverse health effects. The International Agency for Research on Cancer concluded that aflatoxins are genotoxic (DNA-damaging) and carcinogenic to humans (Group 1).  Aflatoxins can cause liver cancer and aflatoxin B₁ is among the most potent ones.  The risk of liver cancer in individuals exposed to both aflatoxins and hepatitis B virus (HBV) infection is reported to be about 30 times higher than that in non-HBV infected individuals.

The Joint Food and Agriculture Organization of the United Nations/WHO Expert Committee on Food Additives recommends that the intake of aflatoxins should be reduced to levels as low as reasonably possible.

Preventive Measures

Since Aspergillus species are ubiquitous in nature, it is not possible to completely eliminate aflatoxins in food which has become contaminated before and/or after harvesting. Other than hot and humid conditions, drought stress, insect damage and poor storage can also contribute to higher occurrence of moulds and consequently high levels of aflatoxins in contaminated food.

Therefore, it is important to implement effective control along the whole food chain to minimise the risk of aflatoxins contamination. Control measures include but are not limited to (1) observe good agricultural practices and good manufacturing practices; (2) discard defective (e.g. mouldy), discoloured or damaged food and do not use them as ingredients for food production; (3) ensure food is stored in cool and dry places e.g. relative humidity below 70%, temperatures below 10℃ can stop Aspergillus species growth and aflatoxins production; and (4) rotate stocks on a first-in-first-out basis.

How Can We Minimise the Risk from Aflatoxins?

Maintaining a balanced and varied diet can avoid excessive exposure to contaminants including aflatoxins from a small range of food items.

Purchase food from reliable sources and store them properly (e.g. follow the manufacturer's instruction to 'keep in a cool and dry place') and not for extended periods of time before being used. Food that looks mouldy or damaged should be discarded.  

We shall continue with other mycotoxins in the next issue.