Antioxidant and antibacterial activity of leaves of Etlingera species (Zingiberaceae) in Peninsular Malaysia

Methanolic extracts from fresh leaves of five Etlingera species were screened for total phenolic content (TPC), antioxidant activity (AOA), and antibacterial activity. Analysis of TPC was done using the Folin–Ciocalteu method. Evaluations of AOA included 1,1-diphenyl-2-picrylhydrazyl free radical-scavenging ability, ferric-reducing antioxidant power (FRAP), ferrous-ion chelating (FIC) ability, and β-carotene bleaching (BCB) activity. Antibacterial activity was screened using the disc-diffusion method. Highest TPC, ascorbic acid equivalent antioxidant capacity (AEAC), and FRAP were found in leaves of E. elatior and E. rubrostriata. Leaves of E. maingayi, with the lowest TPC, AEAC, and FRAP, had the highest FIC ability and BCB activity. Ranking of TPC and AOA of different plant parts of E. elatior was in the order: leaves > inflorescences > rhizomes. Leaves of highland populations of Etlingera species displayed higher values of TPC and AEAC than those of lowland counterparts. Leaves of Etlingera species exhibited antibacterial activity against Gram-positive but not Gram-negative bacteria.