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Morphological and Photosynthetic Parameters of Green and Red Kale Microgreens Cultivated under Different Light Spectra
Microgreens are plants eaten at a very early stage of development, having a very high nutritional value. Among a large group of species, those from the Brassicaceae family, including kale, are very popularly grown as microgreens. Typically, microgreens are grown under controlled conditions under light-emitting diodes (LEDs). However, the effect of light on the quality of grown microgreens varies. The present study aimed to determine the effect of artificial white light with varying proportions of red (R) and blue (B) light on the morphological and photosynthetic parameters of kale microgreens with green and red leaves. The R:B ratios were for white light (W) 0.63, for red-enhanced white light (W + R) 0.75, and for white and blue light (W + B) 0.38 at 230 µmol m−2 s−1 PPFD. The addition of both blue and red light had a positive effect on the content of active compounds in the plants, including flavonoids and carotenoids. Red light had a stronger effect on the seedling area and the dry mass and relative chlorophyll content of red-leaved kale microgreens. Blue light, in turn, had a stronger effect on green kale, including dry mass. The W + B light combination negatively affected the chlorophyll content of both cultivars although the leaves were significantly thicker compared to cultivation under W + R light. In general, the cultivar with red leaves had less sensitivity to the photosynthetic apparatus to the spectrum used. The changes in PSII were much smaller in red kale compared to green kale. Too much red light caused a deterioration in the PSII vitality index in green kale. Red and green kale require an individual spectrum with different proportions of blue and red light at different growth stages to achieve plants with a large leaf area and high nutritional value.
LED Light Quality Affected Bioactive Compounds, Antioxidant Potential, and Nutritional Value of Red and White Cabbage Microgreens
Microgreens are environmentally friendly and have health benefits in addition to their basic nutritional contents. The effect of white (W), white–blue (W + B), and white–red (W + R) light on the bioactive compounds, nutrient composition, and antioxidant potential of red and white cabbage microgreens were investigated using light-emitting diodes (LEDs). The results showed that protein, fat, ash, chlorophylls, and carotenoids were the highest in microgreens under W light, while phenolic compounds were highest in microgreens under W + B light. Supplementation with white light, as well as red or blue light, resulted in higher levels of sugars and total fiber in both white and red microgreens. Twenty-six and thirty-three phenolic compounds were identified in white and red cabbage microgreens, respectively. The identified phenolics belonged to three classes, including phenolic acids, flavonols, and anthocyanins. The antioxidant potential of both cabbage microgreens was determined by four methods (ABTS, DPPH, ORAC, and FRAP). It was found that the highest antioxidant potential was observed in microgreens grown under the W + B light combination. On the other hand, the W + R light combination increased the content of β-sitosterol and campesterol. The results may be helpful in the selection of the type of LED lighting that determines the high nutritional and health-promoting potential of white and red cabbage microgreens.