Effect of supplemental ultraviolet radiation on the carotenoid and chlorophyll composition of green house-grown leaf lettuce (Lactuca sativa L.) cultivars

Eight green leaf and eight red leaf lettuce varieties were grown in a greenhouse under control, receiving supplemental ultraviolet-A (UV-A) (320–400 nm) and supplemental UV-A plus ultraviolet-B (UV-B) (290–320 nm) radiation. The edible portion of the lettuce was frozen, lyophilized and extracted in 80% aqueous acetone for carotenoid and chlorophyll content determination by reverse-phase HPLC. Lutein was the major carotenoid in the lettuce samples with lesser amounts of β-carotene and neoxanthin. In general, supplemental UV-B increased the carotenoid and chlorophyll concentration of green leaf lettuce, while reducing the levels of these compounds in red leaf lettuce. Varieties with relatively high levels of lutein also had high levels of chlorophyll a. Pheophytin a and b levels were higher in green leaf lettuce relative to the red leaf varieties. The up to 10-fold cultivar-specific differences in the levels of the carotenoids in plants grown under identical conditions suggests that the selection of specific leaf lettuce varieties for greenhouse production may enhance their nutritional benefits.