UNDERSTANDING
GENETICALLY MODIFIED (GM) FOODS
Tan Soon Ann, BSc (Chem Eng) MSc, Chemical Process & Biotechnology Department
(now renamed as School of Chemical and Life Sciences), Singapore Polytechnic
In recent years, there have been countless debates and discussions about genetically modified (GM) foods, especially with regards to the benefits and the potential hazards posed to consumers. To date, many crop plants like soybeans and maize have been genetically modified and sold commercially in the United States. Many different types of food ingredients derived from GM crops have also been produced for consumption e.g. the processing of soybeans to soya protein isolate, defatted soya flour, soybean oil and lecithin.
So, what is GM food? GM food, as defined in the European Community (EC) Novel Food Regulation, is "food which is, or which is made from, a genetically modified organism" and which contains genetic material or protein resulting from the modification.
The Technology of Genetic Modification
Basically, genetic modification involves the transfer of the gene of interest from one living thing to another living thing. The gene (DNA) of interest found in the donor organism is first cut out from the whole DNA strand with special enzymes called restriction endonucleases. These pieces are then separated and purified. Next the gene of interest from the donor cell is then incorporated into a carrier system called a vector. This is achieved by cutting the DNA of the vector using similar enzymes to those used for cutting the DNA of the donor organism. The DNA of the donor is then inserted into the vector. Besides plasmid, a virus can also be used as a vector. The vector incorporating the desired gene is then inserted into a bacterial cell. Replication of the vector incorporating the gene of interest can take place in the bacterial cell. This process of replication will produce many cloned copies of the gene of interest. One technique employed for transferring the gene of interest from the donor organism is to insert the cloned copies of the gene to the recipient cell with the aid of a gene gun. Another technique employed is the use of a soil bacterium called Agrobacterium tumefaciens, whose Ti plasmid can be made to play the role of a vector carrying the gene of interest. When employing the bacterium for gene transfer, the tumour forming capabilities of the bacterium’s Ti plasmid has first to be disarmed. Fusion of two cells of different origin is also another technique that can be employed for transferring the gene of interest from its donor to the recipient. Only a small number of recipient plant cells can successfully take up the new DNA. For this reason, a marker gene is often included in the vector. This would make it easier to identify and select those cells that take up the new DNA. One type of marker gene used at the bacterial stage codes for antibiotic resistance, so that the transformed cells containing the new DNA will not die if they are grown in the presence of the antibiotic. There are also other types of marker genes, e.g. those that confer herbicide tolerance to plant cells. Besides marker genes, short DNA sequences called promoters are often incorporated into the vector carrying the gene of interest so as to make it easier for the gene of interest to "express" itself in the final host cell.
Using tissue culture technique, the transformed plant cell is then allowed to develop itself into a whole GM plant. Further selection and rigorous testing procedures are required before the GM plant can be used for food production. GM plants are grown for many generations. This will help ensure that the GM plants can retain and not lose the desired traits conferred upon them. The whole process of selection, testing and propagation of GM plants can take many years to complete.
Not all types of genetic modification of food plants or bacteria involve the insertion of genes from unrelated species. Some genetic modifications of crop plants can take place by ‘switching off’ certain genes, e.g. genes that are involved in the softening of fruits. In this instance, the GM fruit ripens normally, but does not soften. Thus handling damage and losses of the fruits can be minimised.
Other recent developments made in the genetic modification of plants would include the expression of the gene in only certain parts of the plant, such as in the leaves and roots. This is achieved by careful selection of the promoter ‘switch’. For example, genes for pest resistance could be expressed only in the parts of the plant susceptible to attack by the pest, and not in the parts of the particular plant used for food.
Cross Breeding vs Genetic Modification of Crop Plants
Before the advent of genetic engineering, certain desirable traits of plants can be conferred upon from other plants by applying a technique known as cross breeding. However, this technique has its disadvantages - it allows many thousands of genes to be ‘crossed’ with each other at any one time. This often results in the production of plants with several unwanted traits. In contrast, the new technique of genetic modification allows the recipient plant to acquire only the desired trait of the donor. The unwanted traits from its 'donor’ would therefore not be taken up as only the single, well-defined gene, which carries the desired trait is transferred to the recipient plant. In addition, genetic modification also allows desirable gene from other organisms e.g. that of mammals or insects, to be transferred to the recipient plant.
Impact of GM Foods on Food Production and Consumption
It is projected that by 2050 the world population would have doubled to 12 billion (currently estimated at about 6 billion people). Besides the population challenge, future production and supply of food could also be affected with the loss of productive land (to urbanization) and the likelihood of a worsening trend in climatic condition. This situation would undoubtedly put a tremendous strain on the supply of food. However, with the advent of GM technology the problem of food shortage can be partially alleviated or minimised. Currently, GM crops grown commercially are showing positive signs of producing good yield and quality. Typically, the GM crops grown today possess any one or more of these characteristics:
(i) High yielding
(ii) Pest resistant
(iii) Herbicide resistant
Food manufacturers stand to benefit from the application of GM technology. By genetically modifying the food crop, it is possible now to reduce the processing cost of food manufacturing as certain processing steps can either be improved upon or eliminated altogether. For example, tomato purée made from GM tomatoes containing high levels of pectin hold less water. With less water to be removed, less energy for evaporation would be required. This would therefore reduce the cost of producing tomato purée. It is foreseeable to note that genetic modification techniques can also be applied to plants for producing modified starch intended for direct food application, thereby eliminating the chemical modification step.
In the foreseeable future, GM foods can also be made to improve the eating quality of consumers. These qualities would include:
(i) Improved colour and texture of the food product.
(ii) Higher vitamin content levels of fruits and vegetables.
(iii) Improved flavour of many food products.
(iv) Longer shelf-life of fruits and vegetables.
Broccoli, for instance, can be genetically modified to produce higher levels of glucosinates as these compounds are known to reduce the susceptibility of consumers to cancers. Oil crops can also be genetically modified so as to increase the yield and the quality of the oils produced.
Concerns raised over GM foods
Many today have expressed concern over the introduction of GM foods to consumers. There are many issues raised over the use of genetic technology in food production. Some are related to the direct and indirect impact of genetic technology to the environment whilst others are related to the effects of consuming GM foods. As the current platform for discussion is focussed on the health effects of consuming GM foods, the former would not be discussed here. The major concerns of GM foods raised are:
(i) The adverse health effects resulting from consuming the inserted gene of the GM food.
(ii) The inserted gene of GM food may enter into a human cell.
(iii) The inserted gene of a GM food or microorganism may enter into non-GM bacteria.
(iv) The possibility of switching on previously silent genes e.g. the inserted genes can cause the existing genes in plants (or animals) to increase the production of their existing toxins.
(v) The protein coded by the inserted gene is toxic.
(vi) The protein coded by the inserted gene produces an allergic reaction.
Answers to Concerns raised over GM Foods
Firstly, it would be worthwhile to note that consumers are constantly exposed to foreign genes in the foods that they eat. DNA itself is not toxic and therefore consuming it will not pose any adverse health effects on the consumers.
Laboratory experiments have also shown that it is very difficult for foreign genes of GM food to enter into human cells. Attempts made to introduce foreign genes into human cells to replace defective ones, such as those leading to cystic fibrosis, were met with very limited success, even when the conditions for gene transfer were optimised. This tends to support the view that DNA from GM foods is highly unlikely to enter human cells.
Foreign DNA entering the intestinal tract under normal conditions is rapidly broken down into small pieces. The small pieces of DNA are highly unlikely to be functional, as it requires intact foreign DNA to be present for any successful gene transfer to occur. Although there is evidence to support the transfer of free DNA from a GM microorganism to a non-GM one, chances of such a successful transfer are very unlikely to occur. The reasons given are as follows:
(i) The success of DNA transfer and of survival of the recipient bacteria is very dependent on environmental conditions such as temperature, pH and any selection pressures.
(ii) The enzymes present in the bacteria cell can break down the free DNA present.
(iii) The host’s immune system is likely to recognise and destroy the invading microorganism.
So far, there is no evidence to show that the DNA of GM microorganisms can be easily transferred to bacteria under field conditions, although such transfers are possible under laboratory conditions. However, one contentious issue that needs to be dealt with is the use of antibiotic resistance markers in current GM technology. Although the transfer of complete antibiotic resistance marker genes from plant cell into bacteria present in the gut is very unlikely, it should not be completely ruled out. UK’s Advisory Committee on Novel Foods and Processes (ACNFP) recommends the removal of this marker gene once the initial modification step has taken place in the transformed cell.
Finally, it would be worthwhile to note that modified plant cells are analysed to confirm that only the desired genes are present in the newly developed GM plant. Any newly developed GM plant would have to undergo further selection and rigorous testing before it can be used for food production. All these testing and analysis would help ensure that
(i) the genetic modification is stable.
(ii) no undesirable traits of the GM plant are expressed.
(iii) no toxic proteins or proteins that can cause allergies are present in the GM plant.
Food Safety & Labelling in the EC In the EC, GM food is classified as a novel food or novel food ingredient. Like all novel foods, it comes under the control of the EC Regulation No. 258/97. The regulation requires that GM foods be assessed first under a mandatory pre-market safety assessment procedure before they can be sold. Approval for sale would be based upon the following criteria:
(i) that the GM food must not present a danger to the consumer
(ii) that the GM food must not mislead the consumer
(iii) that the GM food must not differ from foods which they are intended to replace, to such an extent that their normal consumption would be nutritionally disadvantageous to the consumer.
With regards to labelling of GM food products, the EC Directive 90/220/EEC requires the labelling of all food products containing or consisting of genetically modified organisms (GMOs). For food and food ingredients obtained from GMOs, labelling is also required when it is scientifically assessed not to be equivalent to an existing food. (The regulation relies heavily on the WHO definition of substantial equivalence in determining whether a GM-derived food is equivalent to its conventionally derived one or not.)
Food Safety & Labelling in the USA
In the USA, the Food and Drug Administration (FDA) is responsible for overseeing the safety of food under the Federal Food Drug and Cosmetics Act (FFDCA). The FFDCA basically places the responsibility on the producer to ensure that the food produced is safe for consumption. In a policy statement on foods derived from new plant varieties, the FDA concludes that existing food legislation is able to adequately address safety issues relating to foods obtained from GM crops. The policy statement also concludes that a special review of GM food would only be needed if the food raised safety concerns.
Although most GM foods do not require specific approval, the FDA however encourages companies to notify details of their products on a voluntary basis. To help companies assess the safety of their GM or GM-derived food products, the FDA has developed a series of decision trees to assist these companies to evaluate on the differences between the new variety and its unmodified equivalent.
In 1992 the FDA addressed its policy statement on labelling of foods obtained from new plant varieties. The FDA held the view that genetic modification techniques do not result in foods that differ from foods developed through other methods of plant breeding. Thus, no labelling is required when the companies producing the foods can show evidence that there is no difference between the GM variety and the conventional equivalent with respect to toxicants, allergens or nutritional value.
Labelling of GM Foods for Export
As expressed by the Codex Committee on Food Labelling (CCFL), a harmonised approach to the labelling of GM foods would be much needed for export purposes. The CCFL had come up with specific proposals at the 1997 meeting. It proposed that for the purposes of labelling, the definition of a GMO should be defined as in accordance with the EC Directive 90/220/EEC. In the case of GM foods, CCFL acknowledged that the consumer should be informed clearly of any new food product obtained by biotechnology, which has specific characteristics not found in its conventional equivalent. It was proposed that the Codex General Standard for the Labelling of Pre-packaged Foods should be revised to include a section on labelling of foods obtained through biotechnology in the mandatory requirements section.
Conclusion
The technology of genetic modification has shown that a GM crop can acquire desirable traits from another organism by simply incorporating the organism’s gene of interest into its own genome. There are various modes of gene transfer, of which the use of a disarmed Ti plasmid of a bacterium A. tumefaciens as vector or the use of a gene gun for direct gene insertion are typical examples. GM crops grown as food are likely to be beneficial to both producers and consumers alike. Besides having improved yields, GM crops could also reduce the manufacturing cost of production and improve the eating quality of consumers. Major differences exist between the US and the EC over the regulatory issues related to the sale of GM foods. The EC is seen as taking a more precautionary stance. To date, there is no evidence to suggest that consuming commercially available GM foods is harmful. Nonetheless, it would still be prudent for the scientific community to adopt a close watch over present and future developments of this new technology and to voice out any legitimate concerns that they are not comfortable about.
Further Reading
P. Peters (1993), Biotechnology: A Guide to Genetic Engineering, Dubuque, IA: Wm. C. Brown Publishers.
S. Roller & S. Harlander (1998), Genetic Modification in the Food Industry, Blackie Academic & Professional
L. Donaldson
& R. May (1999), Health Implications of Genetically Modified Foods,http://www.doh.gov.uk/gmfood.htm