The gene is out of the bottle

Related tags Dna

Authentic, regional and traditional ingredients add quality to foods and attract a premium price. John Dunn discovers how advances in DNA technology ensure that what the food producer offers is pukka

From bangers to burgers and rice to raspberries; from pigs to potatoes and from tuna to tea leaves; and from genetically modified organisms (GMOs) to Jamie Oliver -- checking the authenticity of food ingredients can be a nightmare for food manufacturers. The scope for mislabelling and the substitution of cheaper ingredients along the food chain, inadvertently or deliberately, is huge.

The answer is DNA, those helical strands of genetic material that make every one of the six billion of us on this planet unique. They also make every cow and every coffee bean, every fruit and every fish, every grain of wheat and every gram of locust bean gum, unique too.

It began with GMO testing, but commercial and public testing laboratories are now building up a whole battery of DNA testing techniques to detect precisely what should or should not be in our food. They are also able, somewhat less accurately, to measure the actual amount of something present.

The Food Standards Agency (FSA) has been leading the fight against food fraud in the UK. It has funded the development of DNA tests for checking the authenticity of foods in supermarkets. In its most recent success story, the FSA used DNA testing to examine packets of Basmati rice. Basmati rice retails for twice the price of ordinary rice in the UK.

By using a DNA technique known as microsatellite assay, developed for it by CSL labs in York, the FSA found that of 363 samples of Basmati rice it tested, one in six contained over a fifth of non-Basmati rice.

"You can tell Basmati rice by smelling it, it's got a very strong distinctive aroma," says Sarah Oehlschlager, team leader for cellular and molecular sciences at CSL. "But when it's in a bag you can't smell it, and it also looks similar to other rices."

It has been a similar story for potatoes. Microsatellite DNA has been used to check on the 50 or so varieties of potato sold in the UK. The FSA found that 29% of potatoes sampled were wrongly labelled.

The real problem was King Edwards. DNA testing established that a third (31%) of King Edwards sold in the UK were not King Edwards. They were found to be Ambo, a cheaper, virtually unknown variety.

The FSA has also used DNA testing to check the authenticity of durum wheat for pasta. And it has funded work into a DNA assay method that measures beef, lamb, pork, chicken and turkey as a proportion of the total meat content in food products.

In a government survey of burgers, pies, sausages and other meat products, 15% of samples contained a meat species not declared on the label. With the new test, rogue meat species can now be measured down to 0.5% in raw meats and 5% in canned products.

DNA has also been successfully used to check up on fruit pastes and pulps. The FSA says it has detected 2% rhubarb in a raspberry yoghurt. And it is currently funding work at Campden and Chorleywood Food Research Association (CCFRA) to detect hazel nut oil in olive oil using DNA analysis.

The aim of the FSA's work is to establish and validate an armoury of robust, easy to use and preferably low-cost DNA testing methods that can be used by both public analyst and commercial labs. One of its next priorities is the development of DNA tests for authenticating regional food products such as olive oil, tea and coffee. The aim is to be able to detect the variety or varieties of olive, tea, or coffee bean that define their particular geographical region of origin.

The biggest advantage of DNA testing is that it is extremely specific and sensitive, says Dr Martin Woolfe, head of standards and authenticity in the FSA's food labelling division. "You can pick a needle out of a haystack, so to speak. That's its great strength." And, according to Dr Angus Knight, principle scientist at Leatherhead Food International, the practical limit for detecting DNA is 10 copies of the target DNA sequence. "We're talking here about detecting pico-gram quantities of DNA," he says.

Another advantage is that DNA itself is quite robust. It will survive quite a lot of processing and temperatures up to 120°C, says Woolfe, and so long as some fragments of the target DNA remain, they can be detected. The widely used alternative to DNA testing, particularly for GMOs, is immuno-assays which rely on detecting specific proteins from ingredients. But proteins won't withstand intense processing, says Woolfe. "DNA testing has now replaced immuno-assays in many cases."

But there's still one problem with DNA analysis yet to be solved. It's not very accurate at measuring the amount of the target substance present in a sample, says Woolfe. DNA analysis relies on extracting from samples the specific fragments of DNA that have been identified as ?markers' for the target ingredient or adulterant. These fragments are then amplified or replicated in a polymerase chain reaction (PCR) which keeps on ?photocopying' them until there are enough of them to be visualised and measured.

"The problem is that because you're using a biological reaction (PCR) to multiply up these fragments, it can be difficult to quantify how much DNA there was in the original sample," says Woolfe. "What we have found is that where you are working at the limit of detection, the uncertainty can be 25%. But where you're working with lots of the material present, the uncertainty goes down quite dramatically."

Currently, DNA testing remains the domain of specialist labs with the skills and the equipment to undertake the separation of DNA from a sample, its amplification via PCR, and its visualisation and measurement. A single test can take a day and cost £80 to £150. But things are changing rapidly, says Woolfe, as kits and systems are developed to speed up the process and reduce the skill needed. There are now PCR kits available for amplifying up specific DNA sequences; and DNA chips that speed up the subsequent identification of the DNA signature -- so-called real-time PCR.

Traditionally, identification has been done by staining the DNA on a gel. In the FoodExpert-ID chip system developed by French company bioMérieux, based on the Affymetrix GeneChip, fluorescent DNA probes are embedded in the chip that can detect 33 different species of fish, meat and poultry. After PCR amplification, the DNA is put on the chip and scanned by laser to determine the level of fluorescence and thus the signature of the DNA present. But it is expensive -- £250 or more.

The FSA is currently running trials on another chip system from Agilent. This uses fluorescent primers or markers instead of embedded probes. And according to Woolfe it is relatively cheap -- about £8 a chip -- and the assay itself is simple. It stands a good chance of being taken up by public analyst and other labs, he suggests. The FSA may run it in parallel with the Affymetrix system to see which is the more robust and better value for money.

Although real-time PCR is getting cheaper, the Holy Grail is to be able to detect target DNA without amplification -- to detect that needle in a haystack directly. Mass spectrometry may bring the Holy Grail nearer. According to Steve Garrett of the molecular biology group at CCFRA, mass spectrometry is being developed for detecting target sequences in DNA fragments.

Although it still requires a PCR stage, it is fast -- detection of DNA molecules takes a few seconds rather than hours -- and since the results are based on mass, it promises to be more accurate than current detection methods. It could become the method of choice in the food industry for mass screening and genotyping analysis, suggests Garrett.

Work is also going on to improve the separation stage of DNA analysis by using new extraction techniques that use silica combined with magnetic particles to bind the DNA.

And where does Jamie Oliver fit into all this? Well, Sainbury is using DNA analysis to provide a scientific back-up to its beef traceability scheme. The supermarket's premium ?Traditional' and ?Jamie Oliver 21-day beef' ranges of meat are supplied by Anglo Beef Processors which now stores DNA samples from the animals after slaughter in case Sainsbury needs to trace samples back to individual animals. The supermarket told Food Manufacture that it is now looking at taking the DNA from the small pieces of ear flesh that are produced when a cow is first tagged. fm