LED Lights Influenced Phytochemical Contents and Biological Activities in Kale (Brassica oleracea L. var. acephala) Microgreens

Abstract

Light-emitting diodes (LEDs) are regarded as an effective artificial light source for producing sprouts, microgreens, and baby leaves. Thus, this study aimed to investigate the influence of different LED lights (white, red, and blue) on the biosynthesis of secondary metabolites (glucosinolates, carotenoids, and phenolics) and the biological effects on kale microgreens. Microgreens irradiated with white LEDs showed higher levels of carotenoids, including lutein, 13-cis-β-carotene, α-carotene, β-carotene, and 9-cis-β-carotene, than those irradiated with red or blue LEDs. These findings were consistent with higher expression levels of carotenoid biosynthetic genes (BoPDS and BoZDS) in white-irradiated kale microgreens. Similarly, microgreens irradiated with white and blue LEDs showed slightly higher levels of glucosinolates, including glucoiberin, progoitrin, sinigrin, and glucobrassicanapin, than those irradiated with red LEDs. These results agree with the high expression levels of BoMYB28-2, BoMYB28-3, and BoMYB29 in white- and blue-irradiated kale microgreens. In contrast, kale microgreens irradiated with blue LEDs contained higher levels of phenolic compounds (gallic acid, catechin, ferulic acid, sinapic acid, and quercetin). According to the total phenolic content (TPC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) inhibition assays, the extracts of kale microgreens irradiated with blue LEDs had slightly higher antioxidant activities, and the DPPH inhibition percentage had a positive correlation with TPC in the microgreens. Furthermore, the extracts of kale microgreens irradiated with blue LEDs exhibited stronger antibacterial properties against normal pathogens and multidrug-resistant pathogens than those irradiated with white and red LEDs. These results indicate that white-LED lights are suitable for carotenoid production, whereas blue-LED lights are efficient in increasing the accumulation of phenolics and their biological activities in kale microgreens.

Keywords: LED lights; antibacterial effect; antioxidant effect; carotenoid; glucosinolate; kale microgreens; phenolics.

Figure 1

Expression of carotenoid biosynthesis genes in kale microgreens irradiated with white-, blue-, and red-LED lights. Means with the different letters (a–c) are significantly different at p < 0.05 using DMRT.

Figure 2

Expression of alipathic glucosinolate biosynthesis involves transcription factors in kale microgreens irradiated with white-, blue-, and red-LED lights. Means with the different letters (a or b) are significantly different at p < 0.05 using DMRT.

Figure 3

Representative images showing antibacterial activities of methanol extracts of kale microgreens grown under different LED light illuminations (left, extracts of kale microgreens grown under white-LED light; middle, extracts of kale microgreens grown under blue-LED lights; right, extracts of kale microgreens grown under red-LED lights).