Determination of radical scavenging activity in postharvest microgreens Brassica juncea and Amaranthus tricolor grown under different light spectrum

Abstract

Lighting conditions are one of the most important factors which can influence nutritional value or shelf-life of leafy vegetables. It is beneficial to know the changes in antioxidant activity, during the postharvest stage dependent on light spectrum quality during growth. Thus, the aim was to determine how supplemental light quality during growth can influence the antioxidant activity of microgreens Brassica juncea and Amaranthus tricolor and how it changes during the postharvest storage. The experiments were conducted in a greenhouse (Lat 55°), microgreens were grown in peat substrate with supplemental light-emitting diodes (LEDs) lighting with total PPFD of 250 μmol m-2s-1. 16 h photoperiod and 20±3°C temperature was maintained. For supplemental light different blue 450 nm (B), red 660 nm (R) and white 4000K (W) light compositions were used (B75.6%:R24.2%:W0.02%; R88.9%:B11.1%; R 77.6%:W9.9%:B3.5%). Samples were taken on harvest day, 1, 3 and 5 days after harvest. Microgreens were held in the light (10 μmol m-2s-1), and dark during postharvest storage, 76% air humidity and 4±1 °C temperature was maintained. The highest FRAP antioxidant activity on harvest and during postharvest was determined in mustard microgreens grown under B75.6%:R24.2%:W0.02% LEDs. Compared with the microgreens held in the dark and light, higher antioxidant activity was determined in mustard held in the dark. The highest antioxidant activity was determined in the amaranth microgreens grown under the same (B75.6%: R24.2% :W0.02%) lighting as for mustard, however, there was no significant differences in antioxidant response between amaranth held in the dark or light, as it was demonstrated in mustard. Our findings suggest, that supplemental B75.6%: R24.2% :W0.02% LEDs can significantly increase the FRAP antioxidant activity in mustard and amaranth microgreens during harvest and postharvest stages, compared to other used lighting.