Blue Light Treatment but Not Green Light Treatment After Pre-exposure to UV-B Stabilizes Flavonoid Glycoside Changes and Corresponding Biological Effects in Three Different Brassicaceae Sprouts

Abstract

Ultraviolet-B (UV-B; 280–315 nm) radiation induces the biosynthesis of secondary plant metabolites such as flavonoids. Flavonoids could also be enhanced by blue (420–490 nm) or green (490–585 nm) light. Flavonoids act as antioxidants and shielding components in the plant’s response to UV-B exposure. They are shown to quench singlet oxygen and to be reactive to hydroxyl radical. The aim was to determine whether treatment with blue or green light can alter flavonoid profiles after pre-exposure to UV-B and whether they cause corresponding biological effects in Brassicaceae sprouts. Based on their different flavonoid profiles, three vegetables from the Brassicaceae were selected. Sprouts were treated with five subsequent doses (equals 5 days) of moderate UV-B (0.23 kJ m–2 day–1 UV-BBE), which was followed with two subsequent (equals 2 days) doses of either blue (99 μmol m–2 s–1) or green (119 μmol m–2 s–1) light. In sprouts of kale, kohlrabi, and rocket salad, flavonoid glycosides were identified by HPLC-DAD-ESI-MSn. Both Brassica oleracea species, kale and kohlrabi, showed mainly acylated quercetin and kaempferol glycosides. In contrast, in rocket salad, the main flavonol glycosides were quercetin glycosides. Blue light treatment after the UV-B treatment showed that quercetin and kaempferol glycosides were increased in the B. oleracea species kale and kohlrabi while—contrary to this—in rocket salad, there were only quercetin glycosides increased. Blue light treatment in general stabilized the enhanced concentrations of flavonoid glycosides while green treatment did not have this effect. Blue light treatment following the UV-B exposure resulted in a trend of increased singlet oxygen scavenging for kale and rocket. The hydroxyl radical scavenging capacity was independent from the light quality except for kale where an exposure with UV-B followed by a blue light treatment led to a higher hydroxyl radical scavenging capacity. These results underline the importance of different light qualities for the biosynthesis of reactive oxygen species that intercept secondary plant metabolites, but also show a pronounced species-dependent reaction, which is of special interest for growers.

In Vitro Evidence on Bioaccessibility of Flavonols and Cinnamoyl Derivatives of Cruciferous Sprouts

“…Nowadays, there is increasing consumer concern about the nutritional quality of food, as vegetable origin foods are key for a healthy diet. The role of these plant-based foods in the prevention of a wide array of chronic diseases is associated with their content in bioactive compounds (nutrients and non-nutrients), and to the modification of molecular pathways responsible for the onset and advance of pathophysiological processes [1,2]. Regarding this point, cruciferous sprouts have been demonstrated to be a source of valuable bioactive micronutrients (vitamins and minerals) and phytochemical compounds (glucosinolates and phenolics), related to the prevention of inflammatory, tumoral, or metabolic disorders [3,4].…”

UV and Visible Spectrum LED Lighting as Abiotic Elicitors of Bioactive Compounds in Sprouts, Microgreens, and Baby Leaves—A Comprehensive Review including Their Mode of Action

“…In the same matrix, the authors applied 24 or 36 h of 2 W m −2 UV-B (314 nm), which positively affected the isoflavone accumulation and the gen stimuli related to chalcone synthases, mainly related to the flavonoid biosynthesis [83]. When UV-B and coloured LEDs were combined, Neugart et al [59] showed that 99 µmol m −2 s −1 blue LEDs increased and stabilised the flavonoid content in kale, kohlrabi, and rocket sprouts, whereas 119 µmol m −2 s −1 green LEDs supplemented with UV-B 1.15 W m −2 did not. Gui et al [84] studied the use of UV-B daily treatments (0.7 W m −2 ) during the growth of mung bean sprouts and reported an inhibition of the microbial growth.…”

Effect of Selenium Application and Growth Stage at Harvest on Hydrophilic and Lipophilic Antioxidants in Lamb’s Lettuce (Valerianella locusta L. Laterr.)

“…Phenolic compounds were extracted from lyophilized crushed plant material. Extraction was carried out three times with a 60% (v/v) aqueous methanol solution [59]. The resulting combined extract was filtered and used to determine the total content of hydroxycinnamic acids, the total content of flavonoids, the total content of phenolic compounds, and for high-performance liquid chromatography (HPLC) analysis of individual phenolic compounds.…”