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Food Safety Focus (112th Issue, November 2015) – Food Safety Platform

Cancer-causing Chemicals in Fats and Oils

Reported by Dr. Ivan CHONG, Veterinarian and Ms. Janny MA, Scientific Officer,
Risk Assessment Section,
Centre for Food Safety

In this last article of the series, we will mainly focus on the carcinogenic chemicals, i.e. aflatoxins and benzo(a)pyrene (B[a]P), that may be present in fats and oils.


Aflatoxins are a group of highly toxic mycotoxins produced by fungi of the genus Aspergillus, including A. flavus, A. parasiticus and A. nomius. The four main aflatoxins found in contaminated plant products are aflatoxins B1, B2, G1 and G2.

The International Agency for Research on Cancer (IARC) of the World Health Organization classifies aflatoxins as human carcinogens (Group 1); with the liver being the primary target organ.

Major foods commonly associated with aflatoxin contamination include corn (maize), peanuts (groundnuts), tree nuts as well as other oilseeds. Therefore, it is not surprising that crude vegetable oils, e.g. peanut oil, may contain aflatoxins. As a result, pressing of oil-bearing crops contaminated with aflatoxins may result in their presence in the oil.

Aflatoxins are nearly completely removed by the process of oil refinement. However, proper storage and handling of these oil-bearing crops (e.g. maintaining low moisture levels to prevent the growth of aflatoxigenic fungi and aflatoxins production) are still important in order to minimise the risk, especially for those oils which do not undergo any refining process.


B[a]P is a kind of polycyclic aromatic hydrocarbons (PAHs) and is ubiquitous in the environment. In food, PAHs may be formed via certain processing and cooking methods, e.g. barbecuing, smoking, drying, roasting, frying or grilling. Like aflatoxins, B[a]P has also been classified as carcinogenic to humans (Group 1) by IARC.

Measures are available to lower the levels of B[a]P and aflatoxins in edible fats and oils
Measures are available to lower the levels of B[a]P and aflatoxins in edible fats and oils

Apart from environmental contamination, the occurrence of PAHs in oils is mostly related to the drying processes of the oilseeds where combustion gases may come into contact with them. Both local and overseas surveillance have shown that certain types of oils including peanut oil, corn oil, grapeseed oil, sunflower oil and olive pomace oil, etc. may contain higher levels of B[a]P. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has also concluded that vegetable fats and oils (owing to higher concentrations of PAHs in this food group) as well as cereals and cereal products (owing to high consumption in the diets of many countries) are the major contributors of PAHs intake.

In view of the risks to human health from PAHs formed in foods during processing, Codex has established a Code of Practice for the Reduction of Contamination of Food with Polycyclic Aromatic Hydrocarbons (PAH) from Smoking and Direct Drying Processes. It specifies that direct contact of oilseeds with combustion products during drying processes should be avoided. In addition, the use of active carbon during refining of the oil is a way to reduce the PAHs content after direct drying. The level of B[a]P in oils can be much reduced after oil refining processes while the ultimate level of B[a]P would depend on the conditions under which refining takes place and quality control.


Fats and oils are indeed our good partners in cooking. They not only function as a heat medium but also contribute flavour and texture to our food. With proper treatment and refinement, aflatoxins and B[a]P in these products can be effectively reduced to a low level for human consumption.