Flavonoid content and antibacterial activity on Sabrang Onion Leaf infusion after Ultraviolet‑B Irradiation

The Sabrang Onion or Dayak Onion (Eleutherine palmifolia Merr.) is traditionally used by the Dayak tribe of Kalimantan as herbal medicine, with most studies focusing on its tuber. However, the leaves also contain bioactive compounds, including flavonoids, which may possess antibacterial potential. This study aimed to determine the flavonoid content and antibacterial activity of Sabrang Onion leaf infusion against Escherichia coli following UV-B irradiation. Infusion was prepared by heating leaves at 90°C for 15 minutes, followed by thickening at 70°C for three days. Qualitative flavonoid tests were conducted using Mg-HCl reagent, and quantitative analysis using Thin Layer Chromatography (TLC). Antibacterial activity was assessed using the disc diffusion method at concentrations of 5% and 10%, with chloramphenicol as a positive control. UV-B irradiation for 1-2 hours increased flavonoid content and antibacterial activity, while 3-hour exposure resulted in reduced activity. TLC analysis showed increased flavonoids at 1-2 hours (Rf = 0.885), and decreased flavonoids at 3 hours (Rf = 0.70). The antibacterial activity correlated with flavonoid levels, indicating that UV-B exposure modulates bioactive compound production in Sabrang Onion leaves.