Nutrient Levels in Brassicaceae Microgreens Increase Under Tailored Light-Emitting Diode Spectra

Abstract

To increase the nutritional value and levels of essential minerals in vegetable food, microgreens are promising targets. The metabolic processes of microgreens can be managed with different cultivation techniques, which include manipulating the properties of light derived by light-emitting diodes (LEDs). In this study Brassicaceae microgreens (kohlrabi Brassica oleracea var. gongylodes, broccoli Brassica oleracea, and mizuna Brassica rapa var. Japonica) were cultivated under different light spectral quality, and the metabolic changes insoluble sugars (hexoses and sucrose), ascorbic acid, β-carotene, and contents of non-heme iron (Fe) and its connection with magnesium (Mg) or calcium (Ca) levels were monitored. Plants grew under the primary LED light spectrum (the combination of blue light at 447 nm, red at 638 and 665 nm, and far-red at 731 nm) or supplemented with LED green light at 520 nm, yellow at 595 nm, or orange at 622 nm. The photoperiod was 16 h, and a total PPFD of 300 µmol m-2 s-1 was maintained. Under supplemental yellow light at 595 nm, the content of soluble carbohydrates increased significantly in mizuna and broccoli. Under all supplemental light components, β-carotene accumulated in mizuna, and ascorbic acid accumulated significantly in kohlrabi. Under supplemental orange light at 622 nm, Fe, Mg, and Ca contents increased significantly in all microgreens. The accumulation of Fe was highly dependent on promoters and inhibitors of Fe absorption, as demonstrated by the very strong positive correlations between Fe and Ca and between Fe and Mg in kohlrabi and broccoli, and the strong negative correlations between Fe and β-carotene and between Fe and soluble carbohydrates in kohlrabi. Thus, the metabolic changes that occurred in treated microgreens led to increases in the contents of essential nutrients. Therefore, selected supplemental LED wavelengths can be used in the cultivation of Brassicaceae microgreens to preserve and increase the contents of specific nutritionally valuable metabolites.

Nutrient Supplementation Configures the Bioactive Profile and Production Characteristics of Three Brassica L. Microgreens Species Grown in Peat-Based Media

“…The highest TAA content was 390.6 mg 100 g −1 fw, registered for rocket × C, while the lowest content was 219.5 mg 100 g −1 fw, registered for cabbage × NS. Ascorbic acid is a powerful water-soluble antioxidant [18]; it is a typical example of an imperative secondary metabolite that acts as enzymes 'cofactor, regulates the photosynthesis and cell division, other than being involved in the transduction of signals in plants [10], and inhibits the N-nitroso compounds deriving from nitrite [44]. The TAA values obtained for Brussels sprouts were consistent with those obtained by Xiao et al [45], where they were higher than those registered for cabbage.…”

“…Brassica vegetables are widely planted and consumed all over the world [6][7][8][9][10], including Brussels sprouts, broccoli, cabbage, cauliflower, etc. [6,10], representing a multitude of edible organs such as roots, bulbs, heads and leaves and offering an enormous array of plant secondary metabolites [6]. Cartea et al [8] stated that Brassica vegetables induce health enhancement through their complex blend of antioxidant phytochemicals.…”

Amber, red and blue LEDs modulate phenolic contents and antioxidant activities in eight Cruciferous microgreens

“…Since ROS are constantly produced by metabolically active plants, enhancing compounds like AA and other antioxidant compounds is important for mitigating plant cellular damage. A recent study found supplementary yellow (595 nm) to red and blue components increased AA content in kohlrabi microgreens, but the same effect was not observed in mizuna and broccoli microgreens (Samuolienė et al, 2019). Although our study did not examine the AA content, we determined the antioxidant activity according to an ascorbic acid standard (Figure 4d-f).…”

Seasonal Variation of Health-Promoting Bioactives in Broccoli and Methyl-Jasmonate Pre-Harvest Treatments to Enhance Their Contents

“…The content of total carotenoids in broccoli cultivated in autumn (26 mg/kg) represented a 2.8-fold increase compared to broccoli grown in spring (9 mg/kg). Although the effect of sunlight on the biosynthesis of Brassica carotenoids is not clear [ 10 ], in florets of the broccoli variety ‘Green’ the control group showed higher levels when compared with samples subjected to light of different wavelengths [ 54 , 55 ]. Moreover, other authors have reported that temperatures >15 °C could lead to a decrease in carotenoids [ 8 ].…”