A TEST launched this week should give teeth to the European Union’s strict
labelling rules on genetically engineered foods. It detects minute traces of
genetically modified soya and maize even in highly processed products, a feat
considered impossible until now.
From September last year, retailers in the EU have had to label products
containing GM soya or maize. Britain extended this requirement last week to
include menus in restaurants and cafés. But critics complain that the
lack of an effective test makes the rules meaningless. Even Jeff Rooker,
Britain’s food minister, has conceded that it is not possible to check the GM
content of highly processed food products.
RHM Technology of High Wycombe, Buckinghamshire, says it now has 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, Ranks 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,” says Bob Marsh, managing director of RHM
The test is also the first to measure accurately what percentage of an
ingredient is genetically engineered, claims Marsh. That could be important for
food inspection agencies. The EU is expected to introduce rules which allow food
to be labelled GM-free if less than, say, 2 per cent of the soya or maize within
the product is genetically engineered. This will prevent companies being
penalised for accidental contamination.
The test registered the correct level of contamination in a loaf deliberately
spiked with GM soya flour, says Gordon Wiseman, head of the team that developed
it. Soya accounted for 0.67 per cent of the weight of the test loaf, and just 2
per cent of this fraction had been genetically engineered.
Like other tests for GM foods, RHM ‘s 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, Wiseman’s team has 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 specialised
resin produced by Promega of Madison, Wisconsin.
To establish what percentage of the ingredient is transgenic, Wiseman
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, he compares the amount of cauliflower
mosaic virus promoter with the amount of the natural soya lectin gene.
Wiseman uses specialised 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, he can calculate
the percentage of soya or maize that is genetically engineered.