In the study, conducted by researchers at the John Innes Centre, two groups of cancer-prone rats were fed diets with either red or purple tomatoes. Those in the purple tomato group had significantly longer lifespans.
"This is one of the first examples of metabolic engineering that offers the potential to promote health through diet by reducing the impact of chronic disease," said one of the researchers, professor Cathie Martin.
“And certainly the first example of a GMO with a trait that really offers a potential benefit for all consumers. The next step will be to take the preclinical data forward to human studies with volunteers to see if we can promote health through dietary preventive medicine strategies.”
The researchers ‘turned on’ two genes transplanted from the snapdragon plant to tomato plants and found the resulting deep purple tomatoes registered significantly raised levels of anthocyanins.
Anthocyanins are antioxidants found in many red, blue and purple-coloured fruits, registering particularly high levels in berries such as blackberries and cranberries.
In the body, antioxidants are known to attack free radicals that can cause inflammation and lead to heart and circulation problems as well as being linked to some cancers. Anthocyanins have also been shown to have eye health and diabetes benefits.
While tomatoes already contain boosted levels of the antioxidant, lycopene, this antioxidant is most abundant once tomatoes have been processed and canned, or lightly cooked in oil to help its release.
The pigments from the snapdragon are thought be more water-soluble, with the potential to increase antioxidant release if tomatoes are consumed raw.“Most people do not eat five portions of fruits and vegetables a day, but they can get more benefit from those they do eat if common fruit and veg can be developed that are higher in bioactive compounds,” said professor Martin.
The study is published in the latest edition of Nature Biotechnology.
The hunt for purple tomatoes
The UK researchers are not the first to work on the purple tomato. Work is ongoing at theOregon State University as well as the US-based Sakata Seed company and tomatoes with increased anthocyanin levels are already commercially available, but these tend to be blotchy and their anthocyanin levels are likewise variable.
The Oregaon researchers measures anthocyanin content at 300 micrograms per gram fresh weight in the skin of tomatoes, which does not match that of wild blueberries, but is till very high.
In Europe, 8.5 million tons of tomatoes are cultivated annually with 1.5 million tons sold directly to the consumer and seven million processed for products such as ketchup and sauces.
Scientists at the Texas A&M Department of Horticultural Sciences Vegetable and Fruit Improvement Center, have for many years been working on boosting antioxidant levels of more commonly consumed fruits and vegetables such as tomatoes and carrots.
A purple carrot produced at the Texas institute several years ago has gone on to achieve a moderate level of commercial success in North America, and its work into many fruits and vegetables is ongoing.
Source: Nature Biotechnology
October 26 issue.
'Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors'
Authors: Cathie Martin et al.