The team said the fruit, produced through traditional breeding techniques, could help researchers develop more new varieties of tomatoes with other nutrients, both for home gardeners and for the food industry.
"Tomatoes are second only to the potato in terms of the top vegetable consumed in the world," said Jim Myers, professor of vegetable breeding at Oregon State University. "Per capita use in the US in 2003 was 89 pounds of tomatoes per person. If we could boost the nutritional value of tomatoes, a large part of the population would benefit from that."
Tomatoes are already known to contain lycopene, a carotenoid thought to reduce risk of prostate cancer and fight heart disease. Anthocyanins are the source of the blue, purple and red colour of berries, grapes and some other fruits and vegetables. These pigments also function as antioxidants, believed to protect the human body from oxidative damage that may lead to heart disease, cancer and ageing.
While these natural ingredients have been used as colouring agents in foods for some time, Frost & Sullivan estimates that there is significant potential for growth in polyphenol use as health ingredients. Revenues for the overall European polyphenols market in 2003 were thought to be worth $99 million (€77.88m), with red fruit anthocyanins, leading market expansion alongside green tea flavonoids, and grape and olive polyphenols.
The new research, published in the February issue of the Journal of Heredity, could present competition to makers of polyphenol supplements, currently produced using grape and other fruit extracts. Such companies are already facing intensifying competition and severe price erosion caused by non-European manufacturers entering the market.
Myers and his OSU graduate students characterized the inheritance pattern of a little studied gene in tomatoes called "anthocyanin fruit," or Aft. They crossed a domestic tomato plant with a genetic stock of tomato that included a gene incorporated from a wild relative with anthocyanin-containing fruit and the Aft gene. The result: a domestic-type tomato fruit containing the purple pigment and the Aft gene, opening the door towards developing anthocyanin-rich tomatoes.
The researchers grew the seeds of their new cross of anthocyanin tomato fruit for two generations, backcrossing them with the original parent types. This work led them to confirm that anthocyanin fruits are transmitted in tomatoes by a single dominant gene, Aft.
"We are learning about how anthocyanin genes are expressed in tomatoes, and how we might cross tomatoes to get more nutritional value," explained Myers.
Comparing chemical analyses of the tomatoes with the Aft gene to those without the gene, the OSU plant breeders determined the pigment composition of anthocyanin fruit gene, explained Myers. They also verified that having fruits containing anthocyanin could be inherited through a single gene, Aft.
Another researcher at the university is currently breeding new crosses of tomatoes and analysing the antioxidant activity of not only anthocyanins in the fruits, but also carotenoids. He is also conducting preliminary nutrition studies on humans that have consumed different types of his tomatoes as juice, to see how the various carotenoids are metabolised and which carotenoids prevent oxidation in human plasma.
"The medical, the nutritional and the food research industries all are keenly interested in the health benefits of phytochemicals in all sorts of fruits and vegetables," said Myers."We are happy to find out we can accomplish this in tomatoes using traditional, classical plant breeding techniques."
In Europe, 8.5 million tons of tomatoes are cultivated annually with 1.5 million tons sold directly to the consumer and 7 million processed for products such as ketchup and sauces. But the global tomato processing industry has seen prices tumble in recent years, and although this situation is starting to improve, growing competition from China - now the third largest producer - means many players will be looking for ways to add value to the fruit.