Bioactivities and chemical constituents of leaves of some Etlingera species (Zingiberaceae) in Peninsular Malaysia

2017-01-13T04:25:00Z (GMT) by Chan, Eric Wei Chiang
Based on results of preliminary screening of leaves and rhizomes of ginger species, leaves of Etlingera species were selected for study. Leaves of five Etlingera species were assessed for total phenolic content (TPC), and for antioxidant, antibacterial and tyrosinase inhibition activities. Highest TPC, ascorbic acid equivalent antioxidant capacity (AEAC) and ferric reducing power (FRP) were found in leaves of E. elatior. Leaves of E. maingayi, with the lowest TPC, AEAC and FRP, had the highest ferrous ion chelating (FIC) ability and lipid peroxidation inhibition (LPI) activity. FIC ability of E. maingayi and E. fulgens was much higher than that of young leaves of Camellia sinensis. All Etlingera species studied showed high LPI activity superior to that of young leaves of C. sinensis. TPC and AEAC of leaves of E. elatior and E. maingayi were 7–8 times higher than those of rhizomes. Ranking of TPC and antioxidant activity of the 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 bacteria. Three out of five species displayed strong tyrosinase inhibition activity. Leaves of Etlingera were found to be non-cytotoxic to normal liver and kidney cells. The overall score and ranking were of the order: E. elatior > E. rubrostriata > E. fulgens > E. littoralis > E. maingayi. Leaves of 21 other ginger species belonging to eight genera and three tribes were screened for TPC and AEAC for comparison with those of the five Etlingera species. Compared to Etlingera of the tribe Alpineae, the other ginger species of the same tribe such as Alpinia and Elettariopsis had lower values. Species of Boesenbergia, Curcuma, Hedychium, Kaempferia and Scaphochlamys (tribe Hedychieae) and species of Zingiber (tribe Zingibereae) had much lower values. Effects of five different drying methods on the phenolic content and antioxidant properties of leaves of Alpinia zerumbet, Etlingera elatior, Curcuma longa and Kaempferia galanga were assessed. Thermal drying methods resulted in drastic declines in TPC, AEAC and FRP with minimal effects on FIC ability and LPI activity. Of the non-thermal drying methods, significant losses were observed in air-dried leaves. Freeze-drying resulted in significant gains in TPC, AEAC and FRP for A. zerumbet and E. elatior leaves. Six compounds were isolated from E. elatior leaves and identified as 3-O-caffeoylquinic acid, 5-O-caffeoylquinic acid (chlorogenic acid), 5-O-caffeoylquinic acid methyl ester, isoquercitrin, quercitrin and (+)-catechin. This is the first report of caffeoylquinic acids (CQA) including chlorogenic acid (CGA) in Zingiberaceae. CGA, isoquercitrin and quercitrin, the major compounds, showed DPPH radical scavenging ability but no antibacterial and tyrosinase inhibition activities. Content of CQA of E. elatior, E. fulgens and E. rubrostriata leaves was significantly higher than leaves of Ipomoea batatas, and comparable to flowers of Lonicera japonica. CGA found only in leaves of E. elatior and E. fulgens was significantly higher in content than L. japonica, the commercial source. From leaves of four Etlingera species, highest diversity of essential oil was found in E. rubrostriata. Composition of essential oils in E. elatior and E. fulgens were very different despite having very similar aroma and morphology. Leaves of E. maingayi had the highest yield of essential oils comprising mainly fatty acids that inhibited Gram-positive bacteria. A protocol to produce a CGA standardized extract from leaves of E. elatior has been optimized. Freeze-drying of leaves followed by extraction with ethanol, and fractionation using Diaion HP-20 and Sephadex LH-20 yielded an extract with ~40% w/w purity.