Response of Mustard Microgreens to Different Wavelengths and Durations of UV-A LEDs

Abstract

Ultraviolet A (UV-A) light-emitting diodes (LEDs) could serve as an effective tool for improving the content of health-promoting bioactive compounds in plants in controlled-environment agriculture (CEA) systems. The goal of this study was to investigate the effects of UV-A LEDs at different wavelengths (366, 390, and 402 nm) and durations (10 and 16 h) on the growth and phytochemical contents of mustard microgreens (Brassica juncea L. cv. “Red Lion”), when used as supplemental light to the main LED lighting system (with peak wavelengths of 447, 638, 665, and 731 nm). Plants were grown for 10 days under a total photon flux density (TPFD) of 300 µmol m−2 s−1 and 16-h light/8-h dark period. Different UV-A wavelengths and irradiance durations had varied effects on mustard microgreens. Supplemental UV-A radiation did not affect biomass accumulation; however, the longest UV-A wavelength (402 nm) increased the leaf area of mustard microgreens, regardless of the duration of irradiance. The concentration of the total phenolic content and α-tocopherol mostly increased under 402-nm UV-A, while that of nitrates increased under 366- and 390-nm UV-A at both radiance durations. The contents of lutein/zeaxanthin and β-carotene increased in response to the shortest UV-A wavelength (366 nm) at 10-h irradiance as well as longer UV-A wavelength (390 nm) at 16 h irradiance. The most positive effect on the accumulation of mineral elements, except iron, was observed under longer UV-A wavelengths at 16-h irradiance. Overall, these results suggest that properly composed UV-A LED parameters in LED lighting systems could improve the nutritional quality of mustard microgreens, without causing any adverse effects on plant growth.

Effect of Pre-Harvest Supplemental UV-A/Blue and Red/Blue LED Lighting on Lettuce Growth and Nutritional Quality

“…In the current study, both experiments showed that the UV-A/Blue and RB light treatments increased levels of phytonutrients, including carotenoids, anthocyanins, and TPC compared to the control. Regarding the UV-A/Blue light, our results are consistent with those of Brazaityte et al [43], who used a similar UV-A light with a peak wavelength of 402 nm and reported high levels of TPC in mustard microgreens.…”

Exposure to Salinity and Light Spectra Regulates Glucosinolates, Phenolics, and Antioxidant Capacity of Brassica carinata L. Microgreens

“…In the majority of Brassicaceae species including kale, radish, and broccoli, higher contents of GLs and phenolic bioactive compounds are reported in juvenile stages of plants compared to mature plants [ 1 , 14 , 15 ], where the compounds decrease over time as a result of tissue expansion. The rapid changes in the compounds profiles during germination and early growth of vegetables make early harvesting a particularly relevant factor for maximizing the concentration of these desirable bioactive compounds [ 1 , 14 ].…”

“…The rapid changes in the compounds profiles during germination and early growth of vegetables make early harvesting a particularly relevant factor for maximizing the concentration of these desirable bioactive compounds [ 1 , 14 ]. This has contributed to the rising popularity of young vegetables (sprouts and microgreens), as a source of both health-promoting compounds and as functional foods [ 15 , 16 , 17 ].…”

Combination of Selenium and UVA Radiation Affects Growth and Phytochemicals of Broccoli Microgreens

“…The Se and Se + UVA treatments had slight negative impact on the total S content in broccoli microgreens ( Figure 7 A), indicating that the metabolic pathway of selenium affected sulfur accumulation. Plants receiving a larger amount of UVA had more intensive mineral uptake in mustard microgreens [ 23 ]. Mineral elements in broccoli microgreens seemed to be unaffected by UVA ( Figure 7 ), indicating that the 15 min irradiation of 40 μmol/m 2 /s UVA was not enough to stimulate mineral uptake in broccoli microgreens.…”

“…UVA accounts for 98.7% of the ultraviolet radiation reaching the Earth’s surface [ 16 ] and it is closed to the photosynthetic active spectrum (400 to 700 nm). UVA radiation stimulates phototropins and cryptochromes such as blue light [ 17 ], but it also causes different reactions in plants, which could be useful for improving plant quality without inhibiting growth such as kale [ 18 , 19 ], dropwort [ 20 ], lettuce [ 21 ], sowthistle [ 22 ], and mustard microgreens [ 23 ]. The application of UVA has been particularly effective in enhancing the phytochemicals in plants, but this effect was cultivar- or species-specific.…”