Red–Blue Light-Emitting Diode Spectral Composition Enhances Growth, Yield and Functional Metabolites in Brassicaceae Microgreens: Red Radish (‘Red Rambo’ Raphanus sativus) and Red Mustard (Brassica juncea, MR 408)

This study evaluated the effects of different light-emitting diode (LED) wavelengths on growth, yield, and phytochemical composition of Brassicaceae microgreens, aiming to identify lighting strategies that enhance both biomass production and nutritional quality in controlled-environment agriculture. Red radish (Raphanus sativus ‘Red Rambo’) and red mustard (Brassica juncea ‘MR 408’) were grown under red (R), blue (B), green (G), white (W), and combined LED spectra (R+B, R+G, and G+B) at a constant photosynthetic photon flux density (PPFD) of 300 μmol/m2/s. The R+B treatment produced the best growth performance, resulting in the shortest hypocotyls (red radish: 11.17 cm; red mustard: 7.17 cm) and highest fresh weights (red radish: 92.33 g; red mustard: 54.00 g). The W- light significantly enhanced the anthocyanin accumulation in red radish, including cyanidin-3,5-diglucoside (545.08 mg/100 g dry weight DW) and malvidin-3-glucoside (81.92 mg/100 g DW). In contrast, R+B lighting enhanced carotenoid accumulation in both species, including lutein, trans-β-carotene, and cis-β-carotene, and increased ferulic acid (red radish: 595.02 mg/100 g DW; red mustard: 65.25 mg/100 g DW), epicatechin (radish: 97.63 mg/100 g DW; mustard: 63.21 mg/100 g DW), total glucosinolates (red radish:341.02; red mustard 272.36 μmol/g DW, and ascorbic acid (red radish: 658.78 mg/100 g DW; red mustard: 967.83 mg/100 g DW). Antioxidant activity responded in a species-specific manner, peaking under white light in red radish and under R+B light in red mustard. The results demonstrate that LED spectral composition strongly influences both plant growth and secondary metabolism and that species-specific responses determine the optimal lighting strategy. The R+B lighting is effective for improving biomass production and accumulation of carotenoids, glucosinolates, and ascorbic acid, whereas white light is more effective for enhancing anthocyanin content in red radish. These findings provide a basis for developing lighting strategies to produce high-value Brassicaceae microgreens with targeted nutritional attributes.