The Effect of Uv-a Supplemental Lighting on Antioxidant Properties of Ocimum Basilicum L. Microgreens in Greenhouse

Abstract

The effects of supplemental UV-A LED lighting on growth and antioxidant properties of two varieties of basil (Ocimum basilicum L.) microgreens were determined. Purple-leaf ‘Dark Opal’ and green-leaf ‘Sweet Genovese’ basils were grown in greenhouse (14 days, 22/18 ± 2 °C day/night temperature, 40 ± 5 % a relative air humidity) during winter season. The main lighting system (HPS lamps and natural daylight) was supplemented with ~13.0 μmol m-2 s-1 flux of UV-A 390 nm, and a total PPFD was ~125 μmol m-2 s-1 (16 h photoperiod) for 1 or 7 days before harvest, or entire growth period – 14 days. The results revealed that the influence of UV-A on growth and antioxidant properties depended on basil variety and duration of irradiation. Generally, UV-A irradiation for 7 days significantly (P ≤ 0.05) inhibited growth and hypocotyl elongation of green-leaf basils, and for 14 days of both basil varieties. No significant differences on leaf chlorophyll index were determined. However, leaf flavonol index significantly increased in green-leaf basils after 7 and 14 days UV-A irradiation. The total phenols ant anthocyanin contents significantly decreased after 1 day UV-A irradiation in purple-leaf basils, and the continuous decrease following UV-A irradiation for 7 or 14 days was determined. In addition, UV-A irradiation had negative effects on ABTS radical activity in purple-leaf basils; however, the significantly higher ABTS radical scavenging activity after UV-A irradiation for 1 or 7 days in green-leaf basils were determined. UV-A influenced higher ascorbic acid synthesis in purple-leaf basils after 7 days irradiation, or after 14 days irradiation in both basil varieties. In summary, the supplemental UV-A LED lighting allows to protect basil microgreens from hypocotyl elongation, and enhances antioxidant properties in green-leaf basils. Purple-leaf basils showed to be more sensitive to UV-A irradiation, and less positive effects on antioxidant properties were determined.

Effects of Light on Secondary Metabolites in Selected Leafy Greens: A Review

“…Similarly, Goto et al (2016) obtained an increase in anthocyanins exposing red leaf lettuce to three different UV wavelengths in the order 310 nm >325 nm >340 nm. In contrast to that, Vaštakaitë et al (2015a) showed that anthocyanin content in basil was highest without UV radiation. Similarly, exposing basil to three supplementary UV wavelengths at two intensities, the group of Brazaitytë et al (2015) found highest content of anthocyanins in the control group.…”

“…Rodriguez et al (2014) determined an increased concentration of flavonols in lettuce using supplemental UV FL-Tubes additional to sunlight and supplemental HPSL. Similarly, basil was exhibiting a higher flavonol content when being illuminated with 13 µmol/m 2 /s at 390 nm for 7 and 14 days before harvest (Vaštakaitë et al, 2015a). Brazaitytë et al (2015) found out that supplemental 6 or 12 µmol/m 2 /s at a wavelength of 402 or 390 nm, respectively, produced best results regarding flavonol index.…”

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

“…The rapid development of UV-emitting diodes makes it possible to add single UV-A wavelengths to the light spectrum in CEA lighting, which enables a more accurate assessment of the effect of those single wavelengths. Only few studies have been published on the effects of UV-A on vegetables, and these studies show stimulatory effects of UV-A on the growth of some vegetables (Brazaitytė et al, 2010; Chang and Chang, 2014; Khoshimkhujaev et al, 2014; Brazaitytė et al, 2015; Mickens et al, 2019) but inhibitory (Brazaitytė et al, 2009; Vaštakaitė et al, 2015; Jensen et al, 2018) or no effects on others (Li and Kubota, 2009). Our investigations with a standard visible LED lighting system revealed a positive effect of 390-nm UV-A (for 10 h) and 402-nm UV-A (for 10 and 16 h) on the leaf area of mustard microgreens ( Figure 2 ).…”

“…In general, the application of UV-A radiation has been shown to have an uneven effect on AA accumulation in leafy vegetables. For example, UV-A radiation had no effect on the AA content of baby leaf lettuce (Li and Kubota, 2009) and pea seedlings (Liu and Yang, 2012; Wenke and Qichang, 2012) increased its content in green and purple basil ( Ocimum basilicum ) (Vaštakaitė et al, 2015) and red pak choi and decreased its content in beets and basil-cultivated indoors (Brazaitytė et al, 2015).…”

“…Consequently, the usage of UV wavelengths in CEA is still in its initial stages (Wargent, 2016; Neugart and Schreiner, 2018). Although UV LED lighting is a new technology, research has been conducted on the effects of UV-A LED, as a part of different lighting systems or as a sole source of light, on the growth and metabolism of plants (Li and Kubota, 2009; Samuolienė et al, 2013; Khoshimkhujaev et al, 2014; Brazaitytė et al, 2015; Vaštakaitė et al, 2015; Lee et al, 2014; Brazaitytė et al, 2016; Goto et al, 2016; Rechner et al, 2017; Jensen et al, 2018). Some of these investigations showed that UV-A LED leads to higher total phenolic content, anthocyanin content, ascorbic acid concentration, and antiradical properties in leafy vegetables and herbs (Li and Kubota, 2009; Samuolienė et al, 2013; Brazaitytė et al, 2015; Vaštakaitė et al, 2015; Goto et al, 2016).…”