Metabolites produced by endophytic fungi isolated from Hornstedtia scyphifera (J. Koenig) Steud. and their antioxidant activities

Abstract

Importance of the work: Antioxidant-producing fungi from medicinal plants are still underexplored, especially those originating from wild and uncommon species of the Zingiberaceae.
Objectives: To designate the potential fungal strains exhibiting prominent antioxidant activities through in vitro assay and to identify the putative compounds.
Materials & Methods: Endophytic fungal isolates from the rhizome part of H. scyphifera were identified to the species level based on their internal transcribed spacer (ITS)-rDNA molecular regions. Screening of potential isolates was based on their antibacterial activities against human pathogenic bacteria. The metabolites obtained from batch fermentation of potential strains were evaluated for their antioxidant activities using 2,2-diphenyl-1-picryl-hydrazyl-hydrate, 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonate) and ferric reducing antioxidant power assays. High performance liquid chromatography with diode array detection was used to determine the active compounds.
Results: Two fungal isolates, namely H4 and H7, later identified as Xylaria sp. and Pyrrhoderma sp., respectively, using molecular regions (ITS-rDNA), were selected because they showed strong antagonism against human pathogenic bacteria. The highest antioxidant activity was achieved through the use of MeOH (methanol) > EtOAc (ethyl acetate) > C6 (hexane) by Xylaria sp. H4. Crude EtOAc extract of Xylaria sp. H4 yielded two compounds (chlorogenic acid [CGA] and caffeic acid), while the MeOH extract yielded five compounds (catechin, CGA, caffeic acid, gallic acid and luteolin). Crude EtOAc extract of Pyrrhoderma sp. H7 yielded no compounds, while the MeOH extract yielded the same number of compounds as Xylaria sp. H4.
Main finding: The results provided new information for endophytic fungi that can be exploited as a source of antioxidant compounds and possibly other medicinal aspects from Hornstedtia scyphifera.