Monochromatic red light optimizes total phenolic accumulation and yield in hydroponically cultivated lemon balm (Melissa officinalis L.) microgreens

Abstract

Medicinal plants are crucial to global health, yet challenges in quality and consistency persist, largely due to reliance on wild harvesting. Cultivating medicinal plants like Lemon Balm (Melissa officinalis L.) in controlled environments offers a solution to ensure efficacy and maximize bioactive compounds. This research was intended to find the optimum light conditions for increasing phenol content of Lemon balm microgreen. This study investigated the impact of different LED light spectra—fullspectrum white, red, and various red/blue combinations—on the yield and total phenol content of hydroponically grown Lemon Balm microgreens. Microgreens were harvested 14 days post-sowing. Analyses revealed that monochromatic red light (approx. 651 nm) enhanced dry weight compared to other light treatments. More importantly, red light exposure resulted in the highest accumulation of total phenols, approximately 42% more than the 70R30B red/blue light combination. These findings suggest that, contrary to common assumptions favoring red/blue light combinations, monochromatic red light can be superior for optimizing specific bioactive compounds and yield in certain microgreen species. This research highlights the potential of targeted light strategies in controlled environment agriculture to produce high-quality medicinal plant materials rich in valuable metabolites, offering a novel approach to meet market demands.