Lettuce Carotenoids Affected by UV Light in
By Rosalie Marion
February 23, 2009
Growing the right type of green
leaf lettuce during winter in a greenhouseand exposing it to the right
type of ultraviolet lightcan boost levels of nutritionally beneficial
carotenoids, according to an Agricultural
Research Service (ARS) study.
Dietary carotenoids are biological antioxidants that protect cells and
tissue from damage caused by naturally occurring oxygen free radicals in the
body. Consistently eating carotenoids obtained from recommended servings of
green leafy vegetables, along with a healthy diet, may help reduce the risk of
cataracts and macular degeneration later in life.
The study was conducted by plant physiologists Charles Caldwell (retired)
Britz with the ARS
Human Nutrition Research Center in Beltsville, Md.
In the field, plants express beneficial chemical compounds that are thought
to be a means to protect themselves from the effects of UV radiation. Caldwell
and Britz examined the role of light exposure and cultivar selection on the
relative content of several of these compounds. They studied eight green and
eight red leaf lettuce varieties, each receiving either supplemental
ultraviolet-A (UV-A) light, both UV-A and ultraviolet-B (UV-B) light, or no UV
(receiving only regular light).
Supplemental UV-A plus UV-B greatly increased the carotenoid and chlorophyll
concentrations of the green leaf lettuce varieties, while slightly but
significantly reducing the levels of those compounds in the red varieties.
Interestingly, significantly higher levels of other phenolic phytochemicals
were produced in the red leaf lettuce varieties, compared to the green leaf
lettuce varieties under the same UV treatment conditions.
Among the green leaf lettuce varieties, under identical light and growing
conditions, "Concept" had about 10 times the level of lutein, a
carotenoid, as "Black-Seeded Simpson." Also, the amount of lutein in
two green varieties"Marin" and "Waldmann's Dark
Green"more than doubled after receiving both supplemental UV-A and
UV-B light, when compared to lettuce that received only regular light.
These and other published findings from the study show selecting specific
cultivars for commercial greenhouse production can result in lettuce with major
differences in phytonutrient content.
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture.