Effect of blue LED growing light on enhancing phytonutrients and antioxidants of plant-factory grown kale microgreen

The effects of light-emitting diodes’ (LEDs) light affecting growth and quality of vegetables and fruits at pre- or postharvest have been often reported while for microgreens this is still limited. To study the effect of blue light LEDs on enhancing phytonutrients and antioxidants of kale (Brassica napus ‘Red Russian’) kale microgreen were cultured for 7 days under four different light spectra: red, blue, red + blue (70R:30B) and white (control) with photosynthetic photon flux density (PPFD) of 50 µmol m^‑2 s^‑1 and 16 h photoperiod. After 7 days of light treatment, red LEDs promoted elongation growth as demonstrated by a greater hypocotyl length while kale microgreen grown under red + blue LEDs showed higher fresh and dry weight. Interestingly, blue LEDs alone treatment significantly increased vitamin C content, total flavonoids content, total phenolics compounds and glucosinolate. Those are related to the higher level of DPPH scavenging activity than that of control and red or blue LEDs alone. These results suggests that blue LEDs promoted phytonutrients and antioxidants of kale microgreen without compromising growth and morphology.