Spreading oil on troubled quarters

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As fried fast foods spread into modern Africa, old vegetable oil is being produced in larger and larger quantities. Find out how the illegal resale of used oil for human consumption is creating a cancer time bomb.

By Dr Garth Cambray

In Africa fried foods are becoming increasingly popular. Fried chicken, potato chips and other deep fried foods require large quantities of oil to be used in their preparation. As the vegetable oil is used it becomes darker in colour and degrades until, depending on the moral integrity of the user, it is replaced. What happens to the old oil?

In my experience from collecting old cooking oil for making bio-diesel I have found that in Grahamstown, South Africa, more than half of all old oil produced by food establishments is redistributed into the low income market. This situation is even worse in towns such as King William's town where even greater poverty provides a ready market for old oil. Published data from Malawi suggest this is common in central Africa as well.

Why is this bad?

The basic structure of a triglyceride, such as those which make up the majority of vegetable oil.

If we look at the basic biochemistry of vegetable oil, it consists of a backbone of glycerol (glycerine) with three fatty acids attached to it. In addition there are a few other lesser components such as free fatty acids (ideally less than 1%), vitamin E and pigments such as carotenoids, which give the oil some colour. Typically when cooking we heat the oil to 180ºC at which temperature one gets satisfactory browning of food and not too much oil is absorbed by the food, thus prolonging the life of the volume of oil and hopefully the consumer. However at this temperature the rate of chemical reactions in the oil is many thousands of times higher than at room temperature meaning that the oil will degrade and break down. Aspects of the food will also react with the oil producing compounds of increasingly greater complexity. So the oil goes black.

A comparison of new (left) used from good franchise (middle) and illegally sold used oil from corner café (right).

Several well known fast food franchises have excellent measures in place to ensure that oil is not used for too long. Generally oil from these sources is never more than slightly orange in colour and has limited degradation, which is what we would expect from a well run franchise or chain. These companies also have mechanisms in place to ensure that their old oil does not enter the human market where it could damage their customers and their reputation. In the case of Grahamstown, these businesses provide the oil for experimentation in bio-diesel production - an excellent way of ensuring that the oil in no way enters a human stomach.

Many other businesses however do not adhere to these high standards and use oil until it is burnt completely black. These businesses also tend to either allow their staff to take old oil home for resale to their friends, or in some cases actually repackage old oil and sell it to customers over their counters - which is illegal.

How old oil shortens lives

A 5 litre bottle of illegally sold used highly degraded cooking oil. This bottle cost R15 for five litres.

As oil degrades the percentage of fatty acids which have broken away from the glycerine backbone of the oil increases. Hence a good oil may have a free fatty acid content of 0.3% whereas a heavily used oil may have a free fatty acid content of as high as 5%. The oil pictured in this article which was purchased from a corner café had a free fatty acid content of 4.1%. As the free fatty acid content increases more and more glycerine molecules are present with one or two as opposed to 3 fatty acids attached. Some of these degraded fat molecules can undergo further reactions and become potential carcinogens.

Another very dangerous chemical which forms in vegetable cooking oil is acrylamide. Acrylamide is a recognized carcinogen. Research published in Nature showed that wheat grown on sulphate depleted soil tended to contain high (30 times higher than normal) concentrations of the amino acid asparagine. When this wheat is used to make flower and then batter for onion rings, chicken and so on, it is exposed to high temperatures in the oil. The asparagines react with sugars in the Maillard reaction resulting in the formation of acrylamide.

The problem arises with deep frying of wheat coated foods where some of the wheat particles fall off and remain in the oil - these undergo more complete degradation and as the oil darkens it begins to contain very high levels of acrylamide. If this oil is sold into the human market and is included in food as an ingredient it will have a bad effect on human health.

A vehicle being filled with biodiesel.

The low income markets in Africa are frequently characterised by high percentages of people living with HIV and Aids. Such individuals will not have the ability to fight cancers and are even more susceptible to the carcinogenic effects of old vegetable oil.

Bio diesel as an answer

Many businesses do not know what to do with their old oil. Drums of oil accumulate outside and eventually get stolen. Bio-diesel can be made from old cooking oil and as such the oil is used in car engines where it is burnt and destroyed. For Africa to go forward it is important that our old oil be used to propel our vehicles forwards rather than our health backwards as is currently happening.

More information:

Dr Garth Cambray - editor@scienceinafrica.co.za