Amber, red and blue LEDs modulate phenolic contents and antioxidant activities in eight Cruciferous microgreens

LEDs are applied in controlled environments to produce high-quality microgreens of various nutritional benefit. We investigate different ratios of amber, blue and red LEDs on the synthesis of antioxidant phytochemicals in 8 species of the Brassica genus of microgreens. Microgreens were grown under 8 different LED ratios using combined amber, blue and red ranging from 4.73–58.94%, 20.52–58.94% and 74.36–0.57%, respectively. Results indicated that the effect of the combined lighting on antioxidant activity, total phenolic contents (TPC) accumulation, or its sub-groups total flavonoid contents (TFC) and total anthocyanin contents (TAC), were species-dependent. With increasing amber and blue and concurrently decreasing red lighting, overall positive correlations were observed for TPC, TFC and antioxidant activities (DPPH and FRAP), and overall negative correlations for TAC and ORAC (p < 0.05). Current findings suggest the microgreens can be clustered into 3 groups based on phenolic contents and sensitivity to the lighting: (i) high blue and amber dose-dependence producing high total phenolics and flavonoids content and DPPH antioxidant activity in radish, red Rambo microgreens; (ii) moderate to high sensitivity to overall lighting but no clear dose-dependence to the light in mustards Barbarossa and red kingdom; and (iii) mizunas, pac choi and other microgreens with various responses to lighting.