Antioxidant and Antibacterial Properties of Alpinia galanga, Curcuma longa, and Etlingera elatior (Zingiberaceae)

Antioxidant and antibacterial properties of methanolic extracts, non-polymeric phenolic fractions, and polymeric tannin fractions of leaves and rhizomes of Alpinia galanga and Curcuma longa, and leaves and inflorescences of Etlingera elatior were investigated. Antioxidant properties based on total phenolic content (TPC) and ascorbic acid equivalent capacity (AEAC ) were screened using the Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays, respectively. Antibacterial activity based on minimum inhibitory dose (MID) was tested against Gram-positive Staphylococcus aureus, Micrococcus luteus, and Bacillus cereus using the disc-diffusion method. The effect of ethylenediamine tetraacetic acid (EDTA ) on the antibacterial properties of extracts and fractions was also studied. Extraction yields ranged from 4.1-6.0%. Yields of non-polymeric phenolic (NP) fractions (66-92%) were much higher than that of polymeric tannin (PT) fractions (0.5-10%), suggesting that the former were the major compounds. Highest TPC and AEAC were observed in the PT fraction of A. galanga rhizomes, in the crude extract and NP fraction of C. longa rhizomes, and in the PT fraction of E. elatior leaves. Leaf extracts and fractions of A. galanga and C. longa did not show any antibacterial activity against S. aureus, M. luteus, and B. cereus. Rhizome extracts and fractions of A. galanga and C. longa had no inhibitory effect on M. luteus and S. aureus, respectively. PT fractions of E. elatior leaves and inflorescences displayed no antibacterial activity. With the addition of 0.01 mg/ml of EDTA , extracts and fractions of A. galanga, C. longa, and E. elatior showed moderate, weak, and strong responses, respectively. Strongest antibacterial activity was observed in the PT fraction of A. galanga rhizomes with MID of 0.06 mg/disc against all three bacterial species. PT fractions of E. elatior leaves and inflorescences displayed antibacterial activity with MID of 0.13 mg/disc, which showed no activity prior to the addition of EDTA . The effect of EDTA on the antibacterial activity of extracts and fractions of these three ginger species warrants further investigation.