Scientists in the United Kingdom, working with colleagues in Japan and Germany, have developed tomatoes that are three times richer than normal in ß-carotene, an essential ingredient for health.

Carotenoids are a group of plant pigments responsible for most of the yellow to red colours of fruits, vegetables and flowers. One of them, ß-carotene, is converted by the human body into vitamin A. This is a key nutrient, shortages of which have been linked to coronary heart disease, some cancers and macular degeneration, an eye condition that can lead to blindness. Research also suggests that higher intakes of ß-carotene may be beneficial to the immune system and may reduce skin damage by sunlight. The United Nations Children's Fund (UNICEF) estimates that between 1 and 2 million deaths each year of children one to four years old could be prevented if they received more Vitamin A.

Tomato fruit and its products (e.g. juices, soups, sauces and ketchup) are an important source of carotenoids in the diet. Tomatoes also contain other important nutrients such as vitamin E, vitamin C and flavonoids. Most people, however, consume less than the recommended daily consumption of five portions of fruit and vegetables.

One approach to increasing the dietary intake of carotenoids is to increase their levels in fruit and vegetables. To achieve this goal, it is necessary to understand how plants control the formation and accumulation of carotenoids, using biochemistry, molecular biology and electron microscopy. Because of economic demand and the health promoting constituents of the tomato fruit, it is an important target for this kind of research into increasing nutritional content.

Professor Peter Bramley and his group at Royal Holloway, University of London, have altered the way tomatoes make carotenoids by inserting a gene from a bacterium. The gene converts the compound phytoene into lycopene, the bright red colour in tomatoes, which in turn is involved in the production of ß-carotene. The resulting tomatoes contain up to 3.5 times the normal levels of ß-carotene. The modification does not affect the plant's growth or development and it can be passed on to subsequent generations.

The researchers said that increasing the amount of ß-carotene and other carotenoids in foods was generally thought to be more effective than taking supplements in the form of pills, as other nutrients in the food act synergistically with the carotenoids. There is also evidence that processed and tinned tomatoes and tomato products are more healthy sources of the nutrients because they improve the absorption of carotenoids in the intestine.

Professor Bramley emphasises that there are no plans for the tomatoes to become commercially available. Before this could be considered, trials to determine whether the tomatoes are safe for human consumption will have to be successfully completed.