Scientists have developed a method to make lettuce darker and healthier using ultraviolet (UV) light-emitting diodes (LEDs).

Steven Britz of the U.S. Department of Agriculture and his colleagues used low-power LEDs that exposed lettuce to ultraviolet B (UVB) light for 43 hours. The lettuce was noticeably darker than plants not exposed to the UVB. They have not quantified this effect, but the lettuce darkening increased with the intensity of the light.

Darker lettuce, like spinach, is known to be more nutrient dense than its lighter counterparts, such as iceberg.

When exposed to the sun and ultraviolet rays, lettuce creates UV-absorbing polyphenolic compounds in its outer layer of cells to protect themselves from UV radiation. These polyphenolic compounds, which include flavonoids like quercetin and cyanidin, are powerful antioxidants. Diets rich in antioxidants can provide a variety of health benefits to human beings, from improving brain function to slowing the wear and tear of aging.

Using this method could reduce transportation costs and feed the market in the winter. It may also preserve nutrients in vegetables that have already been harvested.

The research will be demonstrated 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.