Effect of different light intensities on agronomic characteristics and antioxidant compounds of Brassicaceae microgreens in a vertical farm system

Microgreens are vegetable or edible herb shoots harvested in the early stages of development. They have an important number of bioactive compounds and add color, texture, and flavor to dishes and salads. Given their benefits, small size, and high market prices, they can grow in indoor systems, where light is determinant. This study aimed to evaluate the effect of different light intensities on agronomic characteristics, color, chlorophylls and carotenoids content, and antioxidant activity represented by total phenolic content (TPC), eliminate, and antioxidant capacity (AC) in four Brassicaceae species in two colors (green and red). The experiment was conducted in a controlled light-emitting diode (LED) environment growth chamber (day/night temperatures of 25/20 ± 1.2°C, 16 h photoperiod, and 79 ± 2% relative humidity). Three light intensities were used for microgreen growth with the same LED light spectrum: low (120 ± 5.1 μmol m−2 s−1), medium (160 ± 3.6 μmol m−2 s−1), and high (210 ± 5.9 μmol m−2 s−1). Eight g of the seeds of green and red cultivars of cabbage, kale, mizuna, and mustard were sown in a plastic tray (64 cm x 35 cm x 6 cm) with a mixture of peat and perlite (1:2 = v: v). Overall, the high intensity increased dry matter percentage and dry weight, except in green and red kale and green cabbage cultivars. In contrast, low intensity promoted a larger hypocotyl in all species than with high intensity; moreover, it enhanced the cotyledon area in green and red mizuna. Cabbage, kale, and mustard green cultivars were greener under medium intensity, whereas the low intensity enhanced the purple color of mizuna. In addition, chlorophyll a and b increased under low intensity in most species except the red kale and mustard cultivars. The high intensity raises the antioxidant activity, promoting a higher TPC and AC. The findings revealed that the light intensity generated variations in agronomic characteristics, color, chlorophyll content, and antioxidant activity of Brassicaceae microgreens, and the changes were based on the specific species and cultivars.