Nutritional Quality Parameters in Kale Cultivars Are Higher Under Narrow-band LED Light than Under Fluorescent/Incandescent Light

Previous research in our group has shown that narrow-band wavelengths of light from light-emitting diodes (LEDs) can improve the nutritional quality of brassica specialty crops.  The objective of this study was to measure the impact of different light treatments on the concentrations of nutritionally quality parameters among several kale (Brassica oleracea L. var. acephala D.C.) cultivars, and to compare incandescent/fluorescent light with LEDs.  ‘Tuscano’, ‘Red Russian’, ‘Green Lance’, and ‘Redbor F1’ were grown in controlled environment chambers to the 30-day old stage (baby greens). Plants were cultured in hydroponic solutions under two fertility levels and four light treatments.  Light treatments consisted of: 1) 250 µmol×m^-2×sec^-1 of fluorescent/incandescent light; 2) 100 µmol×m^-2×sec^-1 of blue (455-470 nm) / 150 µmol×m^-2×sec^-1  red (627-630 nm) LED light; 3) 100 µmol×m^-2×sec^-1 of blue / 150 µmol×m^-2×sec^-1  red for 22 days, followed by a 10-day exposure of 100 µmol×m^-2×sec^-1 of blue only; and 4) 100 µmol×m^-2×sec^-1 of blue / 150 µmol×m^-2×sec^-1  red for 22 days, followed by a 10-day exposure of 100 µmol×m^-2×sec^-1 of red only.  Light treatments were set to a 16-h photoperiod with an air temperature of 24 °C.  30 days after seeding, plants were harvested, freeze dried, and measured for nutritionally important metabolites.  Kale leaf tissue biomass among cultivars was higher under the high fertility level; however, biomass did not differ among light treatments.  Leaf tissue chlorophyll, lutein, beta-carotene, B, P, S, K, Ca, Cu, Mn, Fe, Zn, and Mo were higher under the high fertility treatment.  Moreover, these same metabolites were significantly higher under the LED light treatments as compared to the fluorescent/incandescent light treatment.  Results demonstrate the ability to increase the nutritional values of 30-day old kale using narrow-band LED light.