This study examines the effect of irradiance level produced by solid-state light-emitting diodes (LEDs) on the growth, nutritional quality and antioxidant properties of Brassicaceae family microgreens. Kohlrabi (Brassica oleracea var. gongylodes, ‘Delicacy Purple’) mustard (Brassica juncea L., ‘Red Lion’), red pak choi (Brassica rapa var. chinensis, ‘Rubi F1’) and tatsoi (Brassica rapa var. rosularis) were grown using peat substrate in controlled-environment chambers until harvest time (10 days, 21/17°C, 16 h). A system of five lighting modules with 455, 638, 665 and 731 nm LEDs at a total photosynthetic photon flux densities (PPFD) of 545, 440, 330, 220 and 110 µmol m−2s−1 respectively were used. Insufficient levels of photosynthetically active photon flux (110 µmol m−2 s−1) suppressed normal growth and diminished the nutritional value of the Brassica microgreens studied. In general, the most suitable conditions for growth and nutritional quality of the microgreens was 330–440 µmol m−2 s−1 irradiation, which resulted in a larger leaf surface area, lower content of nitrates and higher total anthocyanins, total phenols and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging capacity. High light levels (545 µmol m−2 s−1), which was expected to induce mild photostress, had no significant positive impact for most of investigated parameters.

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. © 2013 Society of Chemical Industry

Abstract:The objective of this study was to evaluate the effect of the light emitting diode (LED) spectra on the antioxidant properties of sprouted wheat (Triticum aestivum L.), radish (Raphanus sativus L.), and lentil (Lens esculenta Moenh.) seeds. Lighting experiments were performed under controlled conditions (PPFD -100 µmol m -2 s -1 ; 12 h photoperiod; 27°C). The LED conditions used were: L1 -638 nm; L2 -455 nm, 638 nm, 669 nm, 731 nm (basal components); L3 -basal + 385 nm; L4 -basal + 510 nm and L5 -basal + 595 nm. Wheat and lentil sprouts were shown to accumulate less phenolic compounds and were more sensitive to light spectral differences when compared to radish sprouts. The antioxidant properties and contents of antioxidant compounds in seeds germinated in the dark were significantly lower than LED treated seeds. The higher content of total phenols and significant increase in alpha-tocopherol and vitamin C concentration resulted in altered DPPH free-radical scavenging capacity. Therefore we conclude that the LED spectra, based on basal components supplemented with green (510 nm) light can improve the antioxidant properties of sprouted seeds of lentil and wheat. The highest antioxidant properties of radish seeds were caused by radiation with supplemental amber (595 nm) light.

These results indicate that the application of short-exposure UV-B radiation beneficially influenced both growth parameters and biochemical constituents in young and mature basil plants.

The objective was to evaluate the effect of different combinations of red (638 nm) and blue (455 nm) light produced by solid-state light-emitting diodes (LEDs) on physiological indices (net assimilation rate, hypocotyl-to-leaf ratio, leaf area, leaf dry weight, hypocotyl length and diameter, plant length, developed leaves), variation of photosynthetic pigments and non-structural carbohydrates in radish (Raphanus sativus L., var. ‘Faraon’). Lighting experiments were performed under controlled conditions (total PPFD - 200 μmol m−2 s−1; 16 h photoperiod; 14/18°C night/day temperature). The LED conditions: 638 nm; 638 + 5% 455 nm; 638 + 10% 455 nm; 638 + 10% 455 + 731 nm; 638 + 10% 455 + 731 + 669 nm. Our results showed that radishes grown under red (638 nm) alone were elongated, and the formation of hypocotyl was weak. The net assimilation rate, hypocotyl-to-leaf ratio, and leaf dry weight also were low due to the low accumulation of photosynthetic pigments and non-structural carbohydrates in leaves. The supplemented blue (455 nm) light was necessary for the non-structural carbohydrates distribution between radish storage organs and leaves which resulted in hypocotyl thickening. Red alone (638 nm) or in combination with far-red (731 nm), or red669 for radish generative development was required.