The Influence of Light Wavelength on Growth and Antioxidant Capacity in Pachyrhizus erosus (L.) Urban

Pachyrhizus erosus is a plant that is traditionally used in Asia as a food and herbal medicine. This study examined the impact of light-emitting diodes (LEDs), light-emitting plasma (LEP), and fluorescent lamps (FLs) on the growth, antioxidant properties, and phenolic metabolites of P. erosus. Phenolic compound concentration and composition were determined by high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) system. Radical scavenging activity was measured using stable radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. P. erosus antioxidant activity and phenolic compound composition were improved by the application of LEDs and LEP. Blue LED light also produced significantly higher DPPH radical scavenging activity and ABTS values than the other LED and fluorescent light treatments. In P. erosus seedlings, dry weight, fresh weight, plant height, leaf area, and chlorophyll content were greater under blue LED than under FL light. Furthermore, growth under the blue LED enhanced the epidermal cell length, epidermal cell width, and number of stomata. Antioxidant activity and total phenolic and total flavonoid contents positively correlated in the P. erosus grown under blue LED light condition. Among LED treatments, blue LED produced higher total phenolic compounds, dominated by malonyl daidzin and l-phenylalanine. DPPH assay was highly and significantly correlated with vitexin, salicylic acid, p-coumaric acid, p-hydroxybenzoic acid, l-phenylalanine, daidzein, and daidzin. The present study demonstrated that changes in the growth pattern, antioxidant activity, composition, and metabolite concentration occurred in response to light of different wavelengths in P. erosus seedlings. Thus, LED exposure has the potential to enhance the growth characteristics, metabolite accumulation, and antioxidant properties of P. erosus.