UV LEDs Create Darker Lettuce, Richer in Antioxidants

A recent report by the Optical Society of America (OSA) describes work by a team of plant physiologists to make lettuce darker and redder using UV light-emitting diodes (LEDs), effectively, "giving lettuce a healthy suntan." According to the report, darker color in leafy vegetables is a sign of antioxidants that are thought to have a variety of health benefits. Steven Britz of the U.S. Department of Agriculture in Beltsville, Md., and colleagues will present the research at the 2009 Conference on Lasers and Electro Optics/International Quantum Electronics Conference (CLEO/IQEC), which takes place May 31 to June 5, 2009 in Baltimore.

The dark red tint on red lettuce leaves are said to be the plant kingdom's equivalent of suntan lotion and, when bombarded with UV rays from the sun, the leaf creates UV-absorbing polyphenolic compounds in its outer layer of cells. They help to block UV radiation, which can mutate plant DNA and damage the photosynthesis that allows a plant to make its food. According to the report, polyphenolic compounds,which include flavonoids like quercetin and cyanidin, are also powerful antioxidants. Diets rich in antioxidants are thought to provide a variety of health benefits to humans, from improving brain function to slowing the aging process.

To create the red leaf lettuce plants enriched with these compounds, Britz purchased low-power LEDs that shine with UVB light and exposed the plants to levels comparable to those that a beach-goer would feel on a sunny day; approximately 10 milliwatts per square meter. After 43 hr of exposure, the growing lettuce plants were reported as 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 nm and 296 nm, and absent for longer wavelength UV.

According to the report, UV LEDs could provide a way to enhance this part of the electromagnetic spectrum to produce darker, more colorful lettuces. Britz also discussed the potential for using UV LEDs to preserve nutrients in vegetables that have already been harvested.

What might this research mean to the personal care industry? Perhaps a new approach to imparting the body's own defenses against UV radiation, or imparting a nutricosmetic approach to aging through "super lettuce." While the present report was specific to plant maintenance and nutrition enhancement and did not make a connection to personal care, ideas crop up from all over for the next big invention in personal care.

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