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Unauthorized Importation of Genetically Modified Organisms (GMOs) into Kenya?++Read More

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Glossary

ADI value

The ADI value (Acceptable Daily Intake) quantifies the daily amount of foreign matter in food that a person can ingest over a lifetime without a health risk.

The ADI value is given in milligrams per kilogram body weight and is used for e.g. food additives and pesticide residues.

ADI values are usually based on feeding experiments with rats or mice. The animals are given a diet with varying proportions of the substance under investigation. The aim is to determine the highest level at which no health effect is observed. This No Observable Effect Level (NOEL) is divided by a safety factor to give the ADI value.

The safety factor (usually 100) takes into account various incalculable factors:

  • extrapolation of the NOEL value from trial animals to humans,

  • individual differences – both between the trial animals and in humans,

  • possible unknown interactions between different additives.

Under certain circumstances, the safety factor can be increased; it can also be lower if the substance in question is a natural component of human food.

Agrobacterium tumefaciens

Soil bacterium naturally able to transfer parts of its genetic material to plant cells. It has thus been used as a tool for genetically engineering plants.

Agrobacteria are natural plant parasites. To create a suitable environement for themselves, they insert genes into plant hosts, which cause them to form a proliferation of cells near the soil level (crown gall). The genetic information for tumour growth is encoded on a mobile, circular DNA fragment (plasmid).

When Agrobacterium infects a plant, it transfers so-called T-DNA to a random site in the plant genome.

The natural ability of Agrobacterium tumefaciens to transfer genes is used in genetic engineering. The bacterium is used as a means of transporting foreign genes into plants (vector). To do this, the bacterial T-DNA is cut out of the bacterial plasmid and replaced with the desired foreign gene.

Transferring genes with agrobacteria is a commonly used and reliable method. It works especially well for dicotelydenous plants like potatoes, tomatoes, and tobacco. Agrobacteria are less suitable for introducing foreign genes to crops like wheat and maize.

Alleles

Alleles are the different variant forms of a gene at a particular position (locus) on a chromosome. In classic genetics different alleles are known to be responsible for variations in flower colour (for instance white/red). Each gene generally has several alleles which are characterised by having DNA sequences which differ to a greater or lesser extent.

Allergen

Substance that causes an allergic reaction.

Allergens are found almost everywhere in the environment. They occur in animal hair, pollen, insect bites, house dust mites, pharmaceuticals, and food. Currently, some 20,000 allergens have been identified.

Most allergens in food are proteins of high molecular weight and are rather resistant to gastric acid and digestive enzymes.

An allergenic food may contain several allergens; e.g. there are 15 or more different allergens in soybeans.

Allergy

An overreaction of the immune system caused by a particular substance

The symptoms of allergic reactions often vary; extreme cases can lead to life-threatening anaphylactic shock.

In most cases, allergies are caused by a protein that originates outside the body (allergen). The allergen is perceived by the body as a potentially dangerous, alien component, and an immune response is recruited. This leads to a massive release of pharmacologically active substances, predominantly histamines. Such mis-targeted immune responses are called "true" allergies, sometimes confused with pseudoallergies.

Every "true" allergy is preceded by a phase of sensitisation. First, the immune system adapts to the "alien" substance and produces antibodies. A reaction is triggered only by later contact with the allergen. The first cases of allergies to kiwi fruits did not occur until years after their introduction to the market.

A food allergy is an allergic reaction caused by food constituents or their degradation products, additives, residues, or associated microbial compounds (e.g. fungal or microbial toxins). The uptake of the particular allergen most often occurs via mucous membranes in the mouth and intestine, but can also occur through the skin or by inhalation (e.g. flour dust). Figures on the prevalence of food allergics vary; for adults it is estimated at one to five per cent, while for children under six years estimates range from three to ten percent. In Europe, the most common food allergies are to peanuts, soy, cows' milk, hens' eggs, fish, nuts, crustaceans, and celery. Food allergies are less common than other allergies such as to pollen.

Cross sensitivities can occur when an allergen can be found in more than one source. For example, people allergic to birch pollen often also have allergies to apples or nuts.

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