Scientists have created tomatoes genetically modified to produce antioxidants that could help people to improve their diet and health.

Researchers at the John Innes Centre in Norwich created the crop of purple tomatoes by altering them with genes from snapdragon flowers. In tests, mice that were prone to cancer lived almost a third longer if their diet was supplemented by the modified tomatoes.

The findings, which appear in the Journal Nature Biotechnology, pave the way for a new generation of "functional foods" that could potentially offer protection against serious diseases.

The team, led by Cathie Martin, a professor of plant biology, plans to investigate whether the anti-cancer properties of the tomatoes also protect humans.

The scientists started by plucking genes from snapdragons that are responsible for the deep red pigment in the flower's petals. The colouring is due to an antioxidant called anthocyanin, which is also found in blueberries and blackberries. By inserting the genes into tomato plants, the scientists created a crop so rich in anthocyanin it turned purple as it ripened.

Foods like the “super-tomato” could help people meet the government’s recommendation that everyone should eat five portions of fruit and vegetables a day. Using such foods eating fewer portions may enable people to receive the same benefit.