Lycopene is an antioxidant that is present in red- and pink-coloured fruits and vegetables.
As well as being used as a food colouring, it is also used in supplements.
The role of lycopene in heart health and in reducing the risk of certain cancers is supported by a body of research.
Red tomatoes typically contain about 95 per cent of their lycopene as the all-trans-isomer, reported to be the most stable form.
In tangerine tomatoes, on the other hand, the lycopene is also present as tetra-cis-lycopene, a geometric isomer of all-trans-lycopene.
Geometric isomers refer to two or more substances that have the same chemical make-up but the arrangement of the constituent elements is different, giving the substances different properties.
But evidence is mounting that the tetra-cis-lycopene form is more bioavailable to humans.
The new study, published in the International Journal of Food Sciences and Nutrition , adds to an earlier study by researchers at the Ohio State University and published in the Journal of Agricultural and Food Chemistry .
"Our results suggest that total lycopene concentrations can be increased by substituting tetra-cis-lycopene-rich tangerine tomatoes for common red tomatoes in the diet," wrote lead author Betty Jane Burri from the USDA's ARS.
The USDA researchers, in collaboration with the University of California, Davis, and Yeungnam University (Korea), recruited 21 healthy, non-smoking adults (average age 35.7, 10 men) and fed them lunches containing 300 grams of sauce made from tangerine or red tomatoes per day.
According to the analysis, the tangerine tomatoes contained 34.65 mg of tetra-cis-lycopene per meal, while the red tomatoes contained zero.
The trans-lycopene content of the red tomatoes was 121 mg per meal, compared to 15.54 mg per meal from the tangerine tomatoes.
The overall lycopene content was significantly higher in the red tomato compared to the tangerine variety (194 versus 67.4 mg per meal, respectively).
Using blood samples to quantify bioavailability, data from the double-blind crossover trial showed that, while both sauces were associated with increased blood concentrations of lycopene, the increase of total and tetra-cis-lycopene was greater following consumption of the tangerine tomato sauce.
"Although the common red tomato sauce used in our study contained about three times more lycopene as the tangerine tomato sauce, chili prepared fromthe latter increased blood lycopene concentrations more than the red tomato-based chili," wrote the researchers.
"Therefore, our results show that tetra-cis lycopene from tangerine tomatoes is absorbed more efficiently than trans lycopene from common red tomatoes."
According to Burri and co-workers, absorption of the trans-lycopene isomer may have been enhanced by the presence of the cis isomer.
First report According to the Ohio State study, the reason why the tangerine tomatoes predominantly contain the tetra-cis-lycopene is because they lack a specific enzyme that converts the cis- isomer to the more stable trans form.
This study, reportedly the first report of tangerine tomato consumption in humans, showed that absorption of the cis-form was 2.5 times higher.
A trend looking at different varieties of the fruit is developing, with other researchers reporting the health potential of purple tomatoes.
The purple pigmentation is due to the presence of compounds called anthocyanins - 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.
Source: International Journal of Food Sciences and Nutrition Published online ahead of print 10 April 2008, doi: 10.1080/09637480701782084
"Tangerine tomatoes increase total and tetra-cis-lycopene isomer concentrations more than red tomatoes in healthy adult humans" Authors: B.J. Burri, M.H. Chapman, T.R. Neidlinger, J.S. Seo, B.K. Ishida To access the article online, please click here