The effect of light-emitting diodes photoperiod on tocopherols content in Brassicaceae microgreens

Abstract

The objective of our study was to evaluate the effect of light-emitting diodes (LEDs) light photoperiod on tocopherols content of Brassicaceae microgreens. Tocopherols as primary antioxidants are considered to protect lipids from oxidation; however, their antioxidant activities may differ greatly. Our previous studies revealed that the content of tocopherols may be affected by LEDs light spectra or intensity, and hypothesized to be photoperiod dependent. Red pak choi (Brassica rapa var. chinensis ‘Rubi F1’), tatsoi (Brassica rapa var. rosularis) and mustard (Brassica juncea L. ‘Red Lion’) microgreens were cultivated in controlled-environment growth chamber for 10 days under five photoperiods (8-, 12-, 16-, 20-, 24 h) created by high-power solid-state lighting modules with blue 447-, red 638-, red 665-, far red 731 nm LEDs light. Total photosynthetic photon flux density (PPFD) was ~300 μmol m-2 s-1. The day/ night temperatures at 21±2/17±2 °C and the relative air humidity at 55±5 % were maintained. Tocopherols (α-, β-, γ-, δ-) contents in hexane extracts were evaluated using high-performance liquid chromatography (HPLC) method. Based on the data obtained, the accumulation of tocopherols homologies depended on LEDs light duration; moreover it varied among Brassicaceae species. The significantly higher (P<0.05) contents of all determined tocopherols were evaluated in mustard microgreens grown under 8-, 12-, 16 h LEDs photoperiods. The significantly higher content of α-tocopherol was determined in red pak choi during 8- and 12 h photoperiods, while β- and δ-tocopherols significantly accumulated under 16-, 24 h, and under 20 h photoperiods, respectively. The duration of 24 h photoperiod led to the highest content of α-tocopherol in tatsoi, while under 8- and 12 h photoperiod plants accumulated more β-, γ- and δ-tocopherols. [...]