The effects of LED illumination spectra and intensity on carotenoid content in Brassicaceae microgreens.

The objective of this study was to evaluate the effects of irradiance levels and spectra produced by solid-state light-emitting diodes (LEDs) on carotenoid content and composition changes in Brassicaceae microgreens. A system of five high-power, solid-state lighting modules with standard 447-, 638-, 665-, and 731-nm LEDs was used in the experiments. Two experiments were performed: (1) evaluation of LED irradiance levels of 545, 440, 330, 220, and 110 µmol m(-2) s(-1) photosynthetically active flux density (PPFD) and (2) evaluation of the effects of 520-, 595-, and 622-nm LEDs supplemental to the standard set of LEDs. Concentrations of various carotenoids in red pak choi and tatsoi were higher under illumination of 330-440 µmol m(-2) s(-1) and at 110-220 µmol m(-2) s(-1) in mustard. All supplemental wavelengths increased total carotenoid content in mustard but decreased it in red pak choi. Carotenoid content increased in tatsoi under supplemental yellow light.

LED illumination affects bioactive compounds in romaine baby leaf lettuce.

BACKGROUND: The effect of light quality on phytochemicals in romaine baby leaf lettuce 'Thumper' was investigated in (I) a closed environment and (II, III) a greenhouse (16 h, 21/17 °C): (I) basal (638, 455, 660, 735 nm) LEDs supplemented with UV (380 nm), green (510 nm), yellow (595 nm) or orange (622 nm) LEDs (PPFD of ∼175 µmol m(-2) s(-1) ); (II) high-pressure sodium (HPS) lamps (90 µmol m(-2) s(-1) ) supplemented with blue (455, 470nm) or green (505, 530nm) LEDs (30 µmol m(-2) s(-1) ); (III) at 3 days before harvesting, HPS lamps (90 µmol m(-2) s(-1) ) supplemented with red (638 nm) LEDs (210 µmol m(-2) s(-1) ). RESULTS: (I) Supplemental UV or orange light enhanced phenolic compounds, supplemental UV or green light enhanced α-carotene, and supplemental green light enhanced anthocyanins. All supplemental LED colours had a negative effect on tocopherol and ascorbic acid levels. (II) HPS lighting supplemented with different LEDs was not efficient, since the increase in some compounds did not compensate the decrease in major tested phytochemicals. (III) Short-term irradiation with supplemental 638 nm LEDs before harvesting in the greenhouse did not have a significant effect on phytochemical contents, apart from enhancing tocopherols. CONCLUSION: Wavelength control using LED technology affects the production of secondary metabolites, as the metabolism of many nutrients is light-dependent. The narrow-bandwidth supplemental light effects were diminished by broader-spectrum HPS light or natural daylight in the greenhouse.

LED lighting and seasonality effects antioxidant properties of baby leaf lettuce.

We report on the application of supplementary light-emitting diode (LED) lighting within a greenhouse for cultivation of red, green and light green leaf baby lettuces (Lactuca sativa L.) grown under natural illumination and high-pressure sodium (HPS) lamps (16-h; PPFD-170 µmol m(-2)s(-1)) during different growing season. Supplementary lighting from blue 455/470 nm and green 505/530 nm LEDs was applied (16-h; PPFD-30 µmol m(-2)s(-1)). Our results showed that to achieve solely a positive effect is complicated, because metabolism of antioxidant properties in lettuce depended on multicomponent exposure of variety, light quality or seasonality. The general trend of a greater positive effect of supplemental LED components on the vitamin C and tocopherol contents was in order: 535>505>455>470 nm; on the total phenol content: 505>535=470>455 nm; on the DPPH free-radical scavenging capacity: 535=470>505>455 nm; on the total anthocyanins: 505>455>470>535 nm. Further investigations are needed for understanding the mechanism and interaction between antioxidants and light signal transduction pathways.