Washington, May 19 (ANI): Darker colours in leafy vegetables are often signs of antioxidants that are thought to provide a variety of health benefits to human beings. Now, an American research team has developed a way to make lettuce darker and redder using ultraviolet light-emitting diodes (LEDs).
The dark red tinges on a leaf of red leaf lettuce are the plant kingdom's equivalent of suntan lotion. When flooded with ultraviolet rays from the sun, the lettuce leaf creates UV-absorbing polyphenolic compounds in its outer layer of cells.
Some of these compounds are red and belong to the same family that gives colour to berries and apple skin. They help block ultraviolet radiation, which can mutate plant DNA and damage the photosynthesis that allows a plant to make its food.
Polyphenolic compounds,which include flavonoids like quercetin and cyanidin, are also powerful antioxidants.
In order to create red leaf lettuce plants enriched with these compounds, Steven Britz of the U.S. Department of Agriculture in Beltsville, Md., and colleagues purchased low-power LEDs that shine with UVB light, a component of natural sunlight.
In small quantities, this ultraviolet light allows humans to produce vitamin D, which has been cited for its health benefits.
Britz exposed the plants to levels of UVB light comparable to those that a beach goer would feel on a sunny day, approximately 10 milliwatts per square meter.
After 43 hours of exposure to UVB light, the growing lettuce plants were noticeably redder than other plants that only saw white light.
Though the team has yet to quantify this effect, it appears to increase as the intensity of the light increases. The effect also seems to be particularly sensitive to the wavelength used - peaking at 282 and 296 nanometers, and absent for longer wavelength UV.
"We've been pleasantly surprised to see how effective the LEDs are, and are now testing how much exposure is required, and whether the light should be pulsed or continuous," says Britz.
The research will be presented at the 2009 Conference on Lasers and Electro Optics/International Quantum Electronics Conference (CLEO/IQEC), which takes place May 31 to June 5 at the Baltimore Convention Center. (ANI)