Pulsed LED light increases the phytochemical level of basil microgreens

The effects of pulsed light-emitting diode (LED) lighting on antioxidant and antiradical activities of basil microgreens were investigated. Basil (Ocimum basilicum L. 'Sweet Genovese') was grown in a controlled-environment growth chamber (21/17±2°C day/night temperature; 55±5% relative air humidity) for 14 days after sowing in peat substrate. The main lighting system of high-pressure sodium (HPS) lamps (SON-T Agro, Philips) was supplemented with 20±2 µmol m‑2 s‑1 flux of monochromatic LEDs with peak emission of royal blue 455 nm, blue 470 nm, cyan 505 nm, yellow 590 nm, or red 627 nm (Luxeon® III Star, Philips Lumileds Lighting Company, USA), and the total photosynthetic photon flux density (PPFD) was 200±10 µmol m(‑2) s(‑1) (16 h day(‑1)). Frequencies at 2, 32, 256, and 1024 Hz with a duty cycle of 50% of monochromatic LEDs were applied. Reference plants were grown under HPS lamps supplemented with continuous light of monochromatic LEDs. The results showed that the effects of supplemental pulsed light on total phenolic compounds, total anthocyanins, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging activity and ascorbic acid depended on the wavelength of monochromatic LEDs and frequency. Supplemental lighting of blue 470 nm or red 627 nm at 1024 Hz was the most effective for accumulation of total phenolic compounds as well as total anthocyanins. The highest antiradical activity in basil microgreens treated under all supplemental LEDs, was determined, except red 627 nm at 256 Hz. Accumulation of ascorbic acid was promoted by pulsed light at all frequencies, but higher contents of ascorbic acid were determined under the treatments of 32 and 256 Hz in comparison with other frequencies.