Friday September 28 2012
Pre-cooked chips contain a compound called acrylamide
Frozen chips ‘are a cause of cancer' is the somewhat premature and scary claim in The Daily Telegraph. So when you answer ‘yes’ to that perennial question ‘Do you want fries with that?’ are you really increasing your risk of cancer?
The headlines follow a study designed to look at whether the widely used industrial method of producing frozen (also known as pre-cooked) chips, the ‘french fries’ sold by many take-aways, results in a substance called acrylamide forming inside the chips.
Acrylamide is a chemical compound that Swedish researchers in 2002 discovered was present at high levels in starchy and processed foods such as frozen chips and crisps. Concerns were raised when it was found that acrylamide can cause cancer in mice, but only when the mice were exposed to massive doses – 900 times what a human would typically be exposed to.
This study had two main goals:
- to determine whether the current processes to produce frozen chips on an industrial scale resulted in acrylamide developing inside the chips – which it did
- producing a model to explain what was causing the production of acrylamide
The preparation of frozen chips involves plunging them in boiling water, treating them in sugar solution (consisting of glucose or fructose), part-frying them and then freezing them.
The researchers found that the combination of exposing potatoes to high temperatures and treating them in sugar was mainly responsible for producing acrylamide.
An important point to note is that the claim that acrylamide causes cancer in humans is very much open to debate. Since its discovery, there have been a number large-scale studies into a possible link, with many of these studies having inconclusive results.
The Food Standards Agency (FSA) currently says ‘it is not possible to draw any definitive conclusions about the cancer risks of acrylamide in food’.
Where did the story come from?
The study was carried out by researchers from the University of Reading and the University of Leeds in the UK, and ConAgra Foods in Nebraska, US. No sources of financial support are reported.
The study was published in the peer-reviewed Journal of Agricultural and Food Chemistry.
The news reports reflect the research conducted, though they do not describe the complexities of the mathematical modelling, or that this was specific to thin French fries and not all frozen chips.
Also, the Telegraph’s headline that ‘Frozen chips ‘are a cause of cancer' is inaccurate as it fails to acknowledge the uncertainties that still exist regarding the cancer-causing properties of acrylamide.
Acrylamide is currently defined by the World Health Organisation as ‘probably carcinogenic to humans’.
This means that while no definitive proof has been found that acrylamide is carcinogenic, as a precaution, exposure to acrylamide should ideally be limited to as little as possible.
What kind of research was this?
Acrylamide is a chemical compound naturally produced when foods high in starch are fried or baked at high temperatures. It can be found in potatoes, chips, crisps, bread, and other cereal and wheat products. It is also known that acrylamide is formed as a result of a reaction between the amino acid aspargine and reducing sugars.
Various research projects have been conducted in order to better understand how acrylamide is formed during the cooking process. There is a concern that acrylamide could cause cancer in humans, and the researchers report that it was considered a ‘probable’ carcinogen (in a 1994 publication by the International Agency for Research on Cancer).
The current research is a mathematical modelling study focusing on the level of acrylamide that may be produced during the manufacture of thin chips, ‘French fries’. Due to the thin shape of fries, most of the fried brown colour is formed on the surface of the chip, rather than in the centre. The researchers considered that this is where acrylamide will be formed – where the temperature is highest and moisture levels are low. They used the model to see if they could predict the level of acrylamide that would be formed during the preparation of fries for distribution, and how this would be influenced by the moisture content and cut of the fries, as well as the blanching, heating temperature, and type of sugar solution used. Models such as this can be useful in confirming the process by which acrylamide is formed in cooking.
What did the research involve?
The researchers used potatoes that were cut into thin (shoestring) fries (such as the fries you would find in the larger take-away chains) and prepared them using either glucose or fructose solution, at different concentrations. They were then fried at different temperatures. After frying, the moisture and fat content of the fries was measured using chemical methods. The sugar content, concentration of acrylamide and other amino acids was also measured. They then used the model to see if they could predict the acrylamide content mathematically.
What were the basic results?
The researchers found that the moisture content of the potato strips when entering the partial frying process was the same, regardless of concentration of sugar solution that they were dipped in. Sugar levels in the fries prior to frying increased with the concentration of the sugar solution used. Prior to frying, acrylamide content was low.
After frying, sugar levels went down and acrylamide levels rose. The rate of decrease in sugar levels was more marked when a higher sugar concentration had been used to start with; and the higher the sugar concentration used, the higher the levels of acrylamide formed during frying. This pattern was similar regardless of whether a glucose or fructose solution was used. However, for any given fry colour, fructose-dipped fries contained higher levels of acrylamide than glucose-dipped ones.
They also found that the higher the concentration of the amino acid aspargine (a naturally occuring substance found in a wide range of food stuffs) that was in the potato batch, relative to other amino acids, the higher the amount of acrylamide that would be formed.
How did the researchers interpret the results?
The researchers concluded that their model predicts the concentration of acrylamide that may be formed during the processing of French fries. As they say, an understanding of how sugar preparation and frying influences acrylamide levels is crucial for strategies aimed at trying to reduce levels of this chemical in foods. As they found, the level of fructose relative to glucose in the preparation solution influences levels, as do levels of the amino acid, aspargine.
Acrylamide is a chemical known to be naturally produced when foods high in starch, such as potatoes, chips, crisps, bread and other cereal and wheat products, are fried or baked at high temperatures. The uncertainty about its cancer-causing potential has been debated for some time. As acrylamide is known to be formed as a result of a reaction between the amino acid asparagine and reducing sugars, it is not surprising that higher levels of this amino acid relative to other amino acids were found to result in higher acrylamide levels.
This is a complex mathematical modelling study which was not designed to give firm answers regarding the levels of acrylamide in pre-prepared fries, nor to attribute this to particular brands or distributors, tell us about levels that may be in other frozen chips, home-cooked chips or other pre-prepared products that contain potato or cereal products. Most importantly it cannot confirm the potential health risk from acrylamide.
The UK Food Standards Agency (FSA) reports that it has funded numerous research projects on acrylamide to better understand how it is formed and to look at what measures may be taken to reduce its levels in food. Regarding its cancer causing properties, they say: “Given the uncertainties in exposure and the possible exposure to sources other than food, scientists have concluded that it is not possible to draw any definitive conclusions about the cancer risks of acrylamide in food.”
The FSA also say that they do not advise people to stop eating processed foods that are high in acrylamide, but do advise that a healthy balanced diet should be followed. They also suggest that when making and frying your own chips at home, they should be cooked to a light golden colour; bread should be toasted to the lightest colour acceptable; and when frying or oven-heating pre-prepared foods, such as chips, the manufacturers’ instructions should be followed carefully.
However, the study may serve as a ‘springboard’ to debate on whether there are methods that commerical food manfuacters can employ to reduce the levels of acrylamide in food.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.