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Poisonous Substances Produced by Living Organisms : Toxicity, Allergenicity!
1. Toxicity:
Toxins are poisonous substances produced by living organisms; plants, for example, commonly produce them as protection against insects and other pests. Though in most cases such toxins are produced at a low enough level to enable humans and animals to tolerate them, some widely used foods present hazards of varying degrees of seriousness.
Several varieties of bean are unsafe to eat raw. Some types of mushroom are poisonous, as are rhubarb leaves. Though the toxic genes in potatoes are generally not expressed, it is still not advisable to eat them raw in any quantity .All parts of the tomato plant except the actual fruit are toxic.
In the past, conventional breeding methods have occasionally transferred deleterious characteristics from one variety to another in a way which has resulted in a threat to human health. In the mid-1980s, for example, celery growers in the United States introduced a new strain of insect-resistant celery which promised substantially higher yields to growers. After people handling the celery developed severe skin rashes, however, it was discovered that the plant was shedding psoralens, natural chemicals which become irritants when exposed to sunlight.
In the 1960s, a new variety of potato, the American Lenape, proved to have a burning flavour caused by high levels of glycoalkaloid toxins. Incidents such as these have led one scientist to comment that ‘many of the nightmares predicted for genetically engineered crops have already happened’ as a result of conventional artificial breeding.
In the assessment of GM foods, toxicity is one of the key traits investigated by both biotechnology companies and regulatory bodies. In the unlikely event that a GM food plant was developed which expressed toxins harmful to humans, it would not receive regulatory approval.
2. Allergenicity:
Allergens are substances that provoke an allergic reaction on exposure by consumption or contact. They act where they first come in contact with the body – generally either the respiratory system, the gastrointestinal tract, or the skin. Their effects range from the fatal to the relatively mild and are usually specific to individuals.
No substance is allergenic to everybody, and substances used by millions may be allergenic to just a few. Allergens can be airborne- substances (pollens, dust etc.), infectious agents (bacteria, fungi, parasites), foods (peanuts, shellfish, strawberries, milk products, eggs etc.), as well as chemicals, dyes and other substances.
Some foodstuffs contain several proteins which are commonly found to be allergenic; wheat and milk, for example, each contain around 20 different allergenic proteins. In addition to allergies proper, there can be other adverse reactions to food for which standard allergy tests prove negative.
These are generally forms of food intolerance, i.e. where the body is unable to metabolise the substance. This kind of intolerance is a relatively common response in some individuals to products such as flour and gluten, food colourings and preservatives, and dairy produce.
Recent decades have seen a sharp rise in all forms of allergy – a rise which began long before the introduction of genetically modified crops and foods. Changes in diet, increased exposure to chemicals, and a sanitised way of life which protects people from germs are believed to be among the factors that have contributed to this increase.
Concerns have been expressed that the introduction of new genes into plants might unintentionally introduce proteins capable of causing allergic reactions. The main safeguard against the incorporation of allergenic traits in GM foods lies in the detailed analysis, assessment, and evaluation to which these products are subject before they can be put on the market. A range of tests are carried out to identify possible allergens before they are inserted into plants.
If the foreign DNA comes from a known allergenic food such as peanuts or shellfish, the GM plant is subject to immunological tests. If it does not come from such a source, its amino acid sequence is studied to check for similarities with the sequences of known allergens. The EU Novel Food Regulation also requires that products be clearly labelled if they contain genes that may result in allergenicity, particularly if such genes would not normally be expected to occur in the food.
The only known case where an allergenic protein capable of causing adverse reactions was introduced into a plant by means of genetic modification was detected by tests at an early stage. In the early 1990s, scientists at an American seed company added a gene taken from Brazil nuts to soya beans to enhance their nutritional content.
At the company’s request, an allergy specialist studied the likely impact of the modified soya on patients allergic to Brazil nuts. When it was discovered that it was likely to trigger serious attacks in this group of people, the development of the plant was abandoned.
The scope for using genetic engineering to remove allergens from foods may also grow in the future. Researchers in Japan, for example, have reduced the level of the main allergenic protein in rice by inserting an anti- sense gene to block its production in the plant.