Morphology, Phenolic Content, and Antioxidant Activity of Etlingera fimbriobracteata (K.Schum.) R.M.Sm. and E. philippinensis (Ridl.) R.M.Sm. (Zingiberaceae)

Abstract

Two of the most studied Etlingera species of the ginger family (Zingiberaceae) in the Philippines were Etlingera fimbriobracteata (K.Schum.) R.M.Sm. and E. philippinensis (Ridl.) R.M.Sm. However, little is known about the biochemical analyses of these species to support their potential as ethnomedicinal plants in the country. Thus, this study was carried out to describe the morphology and determine the phenolic content and antioxidant activity of the ethanolic extracts of the two Etlingera species. Data revealed that the two species are correctly identified and their full description, updated distribution, phenology, and habitat and ecology are provided in this paper. The two species are recognizable in both vegetative and reproductive parts. E. fimbriobracteata has reddish color towards the base of the pseudo stem, bright yellow flowers incurved upon maturity, and green sterile bracts that form reddish upon maturity, whereas E. philippinensis has mandarin to deep red inflorescence and has a long outward labellum. The total phenolic content (TPC) expressed as milligram gallic acid equivalent per gram dried sample (mg GAE/g dried sample) revealed the highest phenolics in the leaves (13.20 ± 0.35 in E. fimbriobracteata and 7.21 ± 0.33 in E. philippinensis) than rhizomes (1.44 ± 0.04 in E. fimbriobracteata and 0.46 ± 0.30 in E. philippinensis). Further, total antioxidant activity (TAA) expressed as milligram ascorbic acid equivalent per gram dried sample (mg AAE/g dried sample) was also observed highest in leaves (12.69 ± 0.36 in E. fimbriobracteata and 7.22 ± 0.26 in E. philippinensis) compared to the rhizomes (1.82 ± 0.01 in E. fimbriobracteata and 1.38 ± 0.07 in E. philippinensis). The reducing power (RP) expressed as milligram gallic RP equivalent per gram dried sample (mg GPRE/g dried sample) also revealed higher for the leaves (10.16 ± 2.18 in E. fimbriobracteata and 7.53 ± 0.80 in E. philippinensis) than rhizomes (0.97 ± 0.18 in E. fimbriobracteata and 0.09 ± 0.09 in E. philippinensis). The high contents of phenolic compounds contribute to the antioxidant activity of extracts from the two species. Based on the correlationanalysis, a perfect positive linear relationship was observed among the TPC, TAA, and RP (r= 1, p < 0.001). These imply that E. fimbriobracteata and E. philippinensis could potentially beused as new sources of natural antioxidants.