Woolworths is removing genetically modified foods from its shelves.
Johan Ferreira, head of food technology at Woolworths, has told the parliamentary portfolio committee on the environment that the company has decided to eliminate genetically modified organisms (GMOs) from its products wherever possible.
Where it was not possible to scrap them, the products would be labelled accordingly, he said.
The portfolio committee was being briefed last week on genetic engineering.
Ferreira said Woolworths had been unable to decide whether genetic engineering was a good or a bad thing. However, through its overseas connections, it was aware of pressure for consumers to be given a choice.
"We had to go to each of the more than 3 000 products we market to see whether the ingredients contained GMOs," he told the committee.
"We are about three-quarters of the way through. We are negotiating with local companies and import agents to change to products that don't contain GMOs, but we will end up with some that do and will label them accordingly."
Environment and consumer groups have called on the authorities to introduce the compulsory labelling of foods that contain GMOs, but they have not done so. Woolworths is the first food retailer to take this step.
The company has also produced a brochure: "Genetically modified food: your right to know."
While international debate continues to rage over whether GMOs in food are hazardous or harmless, South Africans have been eating them without knowing it. They have no way of telling because foodstuffs containing GMOs are not labelled.
No fresh fruit or vegetables containing GMOs are sold in South Africa.
However, a variety of foodstuffs that are imported - particularly those that contain maize, soya or their derivatives - and found on supermarket shelves contain GMOs. Soya can be found in many foods, from soup and ice cream to frozen burgers and polony.
GMOs are products of genetic engineering, in which genes from one species are transferred to another species with the intention of improving an organism. For example, the genes of a bacterium are inserted into maize to make it resistant to pests. This crossing of the species barrier could not occur naturally.
Although there is no proof that GMOs are unsafe, there have been no studies into the long-term effects on human health or the environment. Among the possible health risks are increased toxicity of food and the creation of new allergens.
There are also fears that genetically engineered crops may enter the environment through cross-pollination. There is no way of assessing the long-term impact this might have on ecosystems.
In South Africa, genetically engineered soya, tomatoes, potatoes, sugar cane and apples are being grown as trial crops, but none has yet been marketed.
However, genetically modified cotton is being grown and marketed in South Africa.