LED irradiance level affects growth and nutritional quality of Brassica microgreens

摘要

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.