All “oils” ain’t “oils”

Black oil refined for food use (Photo credit: alexpgp – Flickr)

There is a plethora of vegetable oil choices available from a diverse range of sources for use in food. These include olive oil, rapeseed oil, palm oil and a number of oils from any nut or seed you can think of. But this blog post is about black oil pumped up from the earth, sometimes called mineral oil to distinguish it from the vegetable oils. The black oil is treated in refineries and used for many different purposes including petrol, jet fuel, kerosene for heating and as raw material for making plastics. But our interest is in food grade oils and waxes, also called “white” oils, as used by the food manufacturing industry partly because they are cheaper than vegetable oil.

Numerous potential sources of mineral oils in food

The refined black oils can turn up in food as a result of fraud, contamination or from various intentional uses in food production. In 2008, sunflower oil was exported from Ukraine fraudulently diluted with mineral oil. Food in contact with recycled paper and cardboard, wax paper or impregnated jute and sisal bags can be contaminated by residues of mineral oil. Mineral oils are also used directly as release agents for bread and other bakery wares or sugar products and for surface treatment of rice and confectionary. Mineral-based waxes might be used in chewing gum and for surface treatment of certain fruits. There are numerous additional uses through which mineral oils can find their way into food.

Does it matter? Well, at least the European Commission wanted to know and asked the European Food Safety Authority (EFSA) to review the issue. EFSA in response published an opinion in June 2012 stating “that there is potential concern associated with the current background exposure to MOSH in Europe and in particular in the situation of use of white oils as release agents for bread and rolls and to some extent for spraying of grains.”

Many thousands of compounds present in mineral oils

So what does MOSH stand for? As it happens very little is known about the exact composition of the food grade mineral oils and they are often described only by how they behave in relation to their intended use. Specific mineral oil mixtures are produced by physical separation (such as distillation or extraction) and chemical conversion processes (cracking, hydrogenation, alkylation or isomerisation) of the crude black oil. The mixtures might vary from day to day depending on black oil source and particular operating conditions. To make some sense of the mixtures of many thousands of potential compounds EFSA divided the mineral oils into two main types, mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). Food grade mineral oils are produced to contain a minimum amount of MOAH, while technical mineral oil grades can contain between 15-35% of MOAH according to EFSA. Both grades can be found in food, although technical grades to a lesser extent. Thus human MOAH exposure from food is expected to be less than one fifth of MOSH exposure.

Mineral oil residues found in food are of little concern in relation to acute exposure while chronic toxicity is the focus. Some MOAH mixtures are mutagenic and can act as genotoxic carcinogens. EFSA thus stated that MOAH with three or more, non- or simple-alkylated, aromatic rings if found in food were of potential concern, although the risk could not be quantified because of a lack of detailed information. MOSH on the other hand are not carcinogenic, but long chain MOSH can act as tumour promoters at high doses. Liver changes in rats were considered the critical effect on which a margin of exposure could be calculated. EFSA considered that the result pointed to a potential concern for the current background exposure to MOSH via food in Europe.  EFSA believed that a revision of the existing acceptable daily intake for some food grade MOSH would be warranted on the basis of new toxicological information.

Complex issue needing further clarifications

It must be acknowledged that this is a very complex issue. On the one hand, the mineral oil mixtures used deliberately in food manufacturing vary considerably in their composition and thus their potential toxicity. On the other hand, there are also numerous unintended contamination sources of which even less is known. On top of this, analytical methods to detect the presence of mineral oils in food have deficiencies and thus only limited information is available on what amounts can be expected to be found in food. EFSA thus points to the need to collect better information by “identifying sources of contamination at various stages of food production, to design an effective monitoring programme. With respect to the food classes to be included in monitoring, those food groups making a relevant contribution to the background exposure, including the particular cases related to use of white oils, should be taken into account.” They also believed that it was important “to investigate whether other food groups not included in the present evaluation also make a relevant contribution to total chronic exposure.”


Scientific opinion on mineral oil hydrocarbons in food