Effects of pre- and postharvest LEDs treatments on physio-biochemical properties of roselle (Hibiscus sabdariffa L.) microgreens: a preliminary study

Artificial light supplied by light-emitting diodes (LEDs) has been used to promote the bioactive compounds and antioxidants of horticultural crops. Therefore, this study aimed to investigate the effect of pre- and postharvest LED lights treatments on physio-biochemical properties of roselle microgreens (Hibiscus sabdariffa L.). The microgreens were grown under white fluorescent (control), blue, and blue+red LEDs (100 µmol m^-2 s^-1). The harvested microgreens grown from white florescence were then exposed to blue and blue+red (100 µmol m^-2 s^-1) for 8 h day^-1 for 6 days at 10°C. The controls were kept in the dark. For preharvest treatments, controls showed the highest chlorophyll contents (0.3 g kg^-1 FW). However, microgreens grown under blue and combination blue+red LEDs exhibited significantly higher ascorbic acid content (31-34%), DPPH radical scavenging activity (34%) and total phenolic content (21%) than control ones. For postharvest, continuous exposure to postharvest LEDs treatments maintained the chlorophyll content of the microgreens during storage. Additionally, microgreens illuminated with both LEDs treatments showed pronounced increment in ascorbic acid content (25-37% higher than controls). The microgreens illuminated with the combination blue+red LEDs (2.16 g kg^-1 FW GAE) exhibited significantly higher DPPH radical scavenging activity than unilluminated microgreens (1.76 g kg^-1 FW GAE), during 6 days of storage. In conclusion, pre- and postharvest LEDs treatments have potential to promote the phytonutrients in microgreens.