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.
Writing in the Journal of Agricultural and Food Science, researchers from Ohio State University report that 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 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.
According to the new research, led by Steven Schwartz, suggests that the tetra-cis-lycopene form is more bioavailable to humans, and could offer a more interesting source of the nutrient.
"The present results demonstrate high absorption of lycopene when consumed predominantly as cis-isomers, suggesting the consumption of this variety could be a way to increase lycopene absorption and to benefit from its health-associated effects," wrote the authors.
The researchers prepared tomato sauce from the tangerine tomatoes with corn oil to improve palatability and improve absorption of the lycopene - lycopene is a lipophilic compound, which means its absorption is enhanced in the presence of lipids (fats and oils).
The sauces (giving 13 mg of lycopene) were incorporated into a spaghetti meal and fed to 12 healthy volunteers (six women, average age 29.5), and the researchers then measured intestinal absorption of lycopene for almost ten hours after the meal.
Schwartz and his colleagues report that, comparing lycopene absorption from the tangerine variety and a high-beta-carotene variety with lycopene existing predominantly in the all-trans-form, absorption of the cis-form was 2.5 times higher.
"The results revealed efficient absorption of lycopene consumed as cis-isomers when compared to both results from previous studies and lycopene absorption from [a] high-beta-carotene variety with lycopene existing predominantly in the all-trans-form," wrote the researchers.
"To our knowledge, postprandial absorption of lycopene and beta-carotene from these varieties was tested in humans for the first time," they said.
They note however that processing, particularly heating, do appear to affect the lycopene content of the tangerine tomatoes, with the tetra-cis-lycopene level decreasing, while the trans-isomer level was unaffected.
The reason why the tangerine tomatoes predominantly contain the tetra-cis-lycopene, said the researchers, is because they lack a specific enzyme that converts the cis- isomer to the more stable trans form.
"In conclusion, this study supports the hypothesis of lycopene cis-isomers being highly bioavailable. The use of tangerine tomatoes provided a unique source to investigate absorption of cis-lycopene," they said.
The research is in keeping with a trend looking at different varieties of the fruit, with this website reporting recently on research into purple tomatoes. The purple pigmentation is due to the presence of compounds called anthocyanins, and 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.
Source: Journal of Agricultural and Food Science ASAP article, on-line ahead of print; doi:10.1021/jf062337b "Carotenoid absorption in humans consuming tomato sauces obtained from tangerine or high-beta-carotene varieties of tomatoes"Authors: N.Z. Unlu, T. Bohn, D. Francis, S.K. Clinton, S.J. Schwartz