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Specalized metabolites accumulation in mung bean microgreens under the influence of LEDs supplemental illumination

Microgreens are becoming increasingly popular with consumers, not only for their exceptionally intense flavor and color, but also as a functional food with high nutritional value and strong antioxidant activity. Growing microgreens in greenhouses, especially in winter, presents a number of challenges, most notably a lack of light. Light is one of the key factors for optimal plant growth and development, for obtaining adequate yields, but also for the accumulation of various phytochemicals. Quality (wavelength) and photoperiod (duration) are the main light factors that directly affect the morphological characteristics of plants and a number of changes in metabolic functions related to nutrient composition and synthesis of specific metabolites (SM). Photosynthetically active radiation (PAR) includes wavelengths in the range of 400 - 800 nm, with specific photoreceptors of plant cells absorbing red, dark red, blue, and ultraviolet (UV-A) wavelengths. Optimization of the key factors of light, quality and quantity, can significantly positively affect the synthesis of various SM of plant, such as vitamins, polyphenolic compounds, pigments and other compounds of high antioxidant activity. The aim of this study was to determine the influence of red (620 nm) and blue (450 nm) spectra and different photoperiod (12 and 16 h) of supplemental light- emitting diode (LED) illumination on the composition of some SM and antioxidant capacity of mung bean microgreens (Vigna mungo (L.) Hepper)). The study was conducted in a climate chamber with controlled ecological conditions (25 °C, 60% humidity) under supplemental illumination by LEDs. Microgreens mung beans were manually cut at the base of the hypocotyl in cotyledon phenophase at a height of 12 cm and the following SMs were analyzed in the fresh plant material: ascorbic acid content (AsA), total phenolic content (TPC), and antioxidant capacity (by ABTS). The highest levels of AsA (61.74 mg/100 fw) and TPC (223.96 mg GAE/100 g fw) in mung bean microgreens were determined by treatment with LEDs in the red spectrum at a photoperiod of 16 hours. During the photoperiod of 12 hours, higher levels of AsA (50.56 mg/100 g body weight) and TPC (191 mgGAE/100 g body weight) were determined by blue spectrum illumination. Quality and photoperiod had no significant effect on antioxidant capacity. Regardless of the different treatments, antioxidant capacity values were generally high, with an average value of 2374.09 µmol TE /L, indicating that mung bean microgreens represent plant material with high nutritional and functional value. The obtained results indicate that proper management and optimization of quality, i.e. light intensity (selection of appropriate spectrum and photoperiod), can significantly affect the nutritional quality of the plant material and improved synthesis of SMs. From all this, it is clear that further research on specific light factors is needed to optimize the cultivation of plant material with adequate yield and high functional properties.

Vigna mungo (L.) Hepper ; LED supplemental lighting ; ascorbic acid ; total phenols ; antioxidant capacity

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