LED lights influence the volatile and nutritional quality of microgreens of amaranth

Authors: Trandel, Marlee; Bai, Jinhe; Jeffries, Kristen; Poole, Gavin; Hensley, Michael; Schonborn, Wesley; DI GIOIA, FRANCESCO - Pennsylvania State University; Rosskopf, Erin

Submitted to: Florida State Horticultural Society Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/30/2023
Publication Date: 12/31/2023
Citation: Trandel, M.A., Bai, J., Jeffries, K.A., Schonborn, W.A., Hensley, M.E., Di Gioia, F., Rosskopf, E.N. LED lights influence the volatile and nutritional quality of microgreens of amaranth. Florida State Horticultural Society Meeting. 136:116. 2023. https://doi.org/10.32473/fshs.136.1.138253.
DOI: https://doi.org/10.32473/fshs.136.1.138253

Interpretive Summary: Microgreens are becoming very popular because they are nutrient dense, colorful, and flavorful. Microgreens are often grown using light emitting diode (LED) as the light source. Red (R) and blue (B) LED lights are commonly used for growing microgreens. Increasing evidence supports the addition of green (G) LED light to R:B LED lighting to enhance plant growth and nutrient content, but many microgreen species have not been evaluated. Amaranth (Amaranthus cruentus) was grown in greenhouse experiment using a randomized complete block design (RCBD) with four light treatments, LED R:B 80:20, LED R:G:B 70:10:20, and LED white (LED control) at 300 PPFD with one ambient light treatment. A clear separation of flavonoid and carotenoid contents were seen, with LED white separated from R:B and R:G:B. R:B and R:G:B increased both flavonoid and vitamin content. For amaranth, R:B and R:G:B LED light treatments were both suitable for increased phytonutrient composition when compared to white or ambient light.

Technical Abstract: Microgreens are known for their vibrant colors, delicate textures, and concentrated flavors and nutrients. Red (R) and blue (B) LED lights are commonly used for growing microgreens. Increasing evidence supports the addition of green (G) LED light to R:B LED lighting to enhance plant growth and nutrient content, but many microgreen species have not been evaluated. The objective of this research was to understand the effects of R:G:B light in comparison with R:B light and white LED/ambient light on individual microgreens. Amaranth (Amaranthus cruentus) was grown in greenhouse experiment using a randomized complete block design (RCBD) with four light treatments, LED R:B 80:20, LED R:G:B 70:10:20, and LED white (LED control) at 300 PPFD with one ambient light treatment. For all LED treatments, the experiment shelves were covered by opaque and reflective clapboard. Crop yield, hypocotyl length, canopy color (L*, a*, and b*), minerals, volatiles, flavonoids, and carotenoids were analyzed as well as total antioxidant activity, total phenolics, anthocyanins, and chlorophylls. Hypocotyls were longer and thinner under ambient light. R:B enhanced redness (a*), while green light did not cause an additional effect. Thirty-one volatile compounds were identified, including eight aldehydes (peak area size ratio to total area, 51%), seven alcohols (5%), five ketones (2%), four benzenes (19%), two sulfur compounds (2%), and five other compounds. The most abundant compounds are hexanal (22%, peak area ratio to total peak), octyl 4-ethylbenzonate (17%), E-2-hexenal (11%), Z-3-hexenal (9%), and they were not impacted by different light treatments. Cluster analysis clearly divided the volatile response groups to two: R:B and R:G:B groups versus the white LED and the ambient light group. The only compound which was stimulated by R:G:B was 3-methyl-3-buten-1-ol (a sweet fruity note). No significant differences were found in the antioxidant activity and total assays among LED treatments. Twenty flavonoids, eight carotenoids and three vitamins were found. Principle component analysis was performed on flavonoid and carotenoid data. A clear separation of flavonoids and carotenoids were seen, with LED white separated from R:B and R:G:B. R:B and R:G:B increased flavonoid and vitamin content. For amaranth, R:B and R:G:B LED light treatments were both suitable for increased phytonutrient composition when compared to white or ambient light.