Test can enforce European rules on labelling genetically engineered foods
To give teeth to the European Union's strict labelling rules on genetically engineered foods, a British company has launched a test to detect minute traces of genetically modified (GM) soya and maize even in highly processed products, reports New Scientist. From September last year, retailers in the EU have had to label products containing GM soya or maize. Britain has extended this requirement to include menus in restaurants and cafés. But critics complained that the lack of an effective test makes the rules meaningless. However, RHM Technology of High Wycombe, Buckinghamshire, England, has introduced a test that detects traces of GM ingredients even in heavily processed products, such as those containing soya oil or lecithins. RHM developed the test to allow its parent company, Rank Hovis McDougall, to monitor the GM content of its own products, which include cakes, sauces, bread and jams. The company will also be able to see if its rivals are failing to label products containing GM ingredients. "We've even found some contaminated items in health food stores," said RHM managing director Bob Marsh. The test is also the first to measure accurately what percentage of an ingredient is genetically engineered, claimed Mr Marsh. That could be important for food inspection agencies. The European Union is expected to introduce rules which allow food to be labelled GM-free if less than, say, 2% of the soya or maize within the product is genetically engineered. This will prevent companies being penalized for accidental contamination. "The test registered the correct level of contamination in a loaf deliberately spiked with GM soya flour," said Gordon Wiseman, head of the team that developed it. Soya accounted for 0.67% of the weight of the test loaf, and just 2% of this fraction had been genetically engineered. Like other tests for GM foods, the RHM test detects DNA sequences unique to the transgenic ingredient. These include the cauliflower mosaic virus promoter, the "switch" for activating added genes. To generate the millions of copies needed for detection and analysis, the DNA fragments in a sample must be multiplied using the polymerase chain reaction (PCR). But food processing degrades DNA. Another problem is that substances in processed food, such as salt, calcium and polysaccharides, block PCR. To overcome these obstacles, Mr Wiseman's team designed the test to recognise much smaller fragments of the same genes, which survive processing. The PCR-blocking substances are removed by purifying the DNA with a specialized resin produced by Promega of Madison, Wisconsin. To establish what percentage of the ingredient is transgenic, the test measures the content of two genes from each sample. One is unique to the genetically engineered ingredient, and one occurs in the transgenic and the natural material. In tests for GM soya, it compares the amount of cauliflower mosaic virus promoter with the amount of the natural soya lectin gene. The test uses specialized fluorescent probes to monitor accumulation of these gene replicas at each successive cycle of PCR. By comparing the intensity of the glow of the probes for the natural and transgenic sequences, it can calculate the percentage of soya or maize that is genetically engineered.