Light source and spectra influence the phytochemical profile of amaranth microgreens

Radiation source and spectrum are important drivers for plant primary and secondary metabolism. There is great interest in understanding how light source and light emitting diode (LED) spectra affect the quality and nutritional profile of nutrient-dense crops such as microgreens. In this study, amaranth microgreens were cultivated under controlled environment using various light conditions: sole source LED red:green:blue (R:G:B) at the ratio of 70:10:20, R:B at 80:20, white (W), or ambient light (greenhouse solar radiation). Microgreen samples were extracted and analyzed for phenolics, carotenoids, and widely targeted metabolomic profiling via LC-MS/MS. Comprehensive metabolomic analyses revealed the presence of 9 vitamins, 6 carotenoids, 17 phenolics, 22 amino acids, 5 nucleosides, 5 sugars and 4 organic acids. When grown under LED treatments, including R:B, R:G:B and W, the microgreens exhibited enhancements in red color (greater hue and/or a∗) and shorter hypocotyl length. Notably, microgreens treated with R:B and R:G:B contained higher levels of vitamin E, vitamin C, and carotenoids, but lower levels of phenolic compounds and B vitamins. Microgreens grown under R:B also demonstrated higher sugars and acids compared to W and ambient light. However, amaranth cultivated under R:B and R:G:B exhibited lower amino acid and nucleoside content, which are known to contribute to nutritive values for human consumption. In the current study, R:B and R:G:B did not stimulate higher total phytonutrient production in amaranth suggesting further research testing higher G ratios (11%–20%) and different light intensities and exposure times are needed.