Phenolic and flavonoid contents and antioxidant activity of an endophytic fungus Nigrospora sphaerica (EHL2), inhabiting the medicinal plant Euphorbia hirta (dudhi) L

Abstract

Since endophytic fungi are pivotal sources of various bioactive natural compounds, the present study is aimed to investigate the antioxidant compounds of the endophytic fungus Nigrospora sphaerica isolated from a pantropical weed, Euphorbia hirta L. The fungus was fermented in four different media and each filtered broth was sequentially extracted in various solvents. Crude extracts collected from different solvents were subjected to phytochemical analysis and antioxidant activity. The total phenolic content (TPC) and total flavonoid content (TFC) were maximal in ethyl acetate crude extract (EtOAcE) of endophyte fermented in potato dextrose broth (PDB) medium (77.74 ± 0.046mgGAE/g and 230.59 ± 2.0 mgRE/g) with the highest 96.80% antioxidant activity. However, TPC and TFC were absent in hexane extract of Czapek Dox broth (CDB) medium exhibiting the lowest 4.63 ± 2.75% activity. The EtOAcE (PDB) showed a positive correlation between TFC and antiradical activity (R² = 0.762; P < 0.05), whereas a high positive correlation was noticed between TPC and antioxidant activity (R² = 0.989; P < 0.05). Furthermore, to determine the antioxidant activity, EtOAcE (PDB) was subjected to TLC bioautography-based partial purification, while GC/MS analysis of the partial purified extract was done to confirm the presence of phenolics along with antioxidant compounds that resulted in the detection of 2,4-Di-tert-butylphenol (13.83%), a phenolic compound accountable for the antioxidant potential. Conclusively, N. sphaerica is a potential candidate for natural antioxidant.

Keywords: Antioxidant activity; Compounds purification; GC–MS analysis; N. sphaerica; Phytochemical analysis; TLC bioautography.

Fig. 1

Schematic diagram showing sequential extraction

Fig. 2

TLC plates of ethyl acetate extract (PDB) of Nigrospora sphaerica visualized under visible light before and after derivatization (0.2 Mm DPPH solutions), UV light at 254 nm (green panel) and 366 nm (blue panel)

Fig. 3

a ABTS free radical inhibiting potential of purified ethyl acetate extract (PDB) of Nigrospora sphaerica and positive control using different concentrations (12.5–400 µg) and b DPPH free radical scavenging potential of purified ethyl acetate extract (PDB) of N. sphaerica and positive control using different concentrations (12.5–400 µg)

Fig. 4

a Chromatogram of GC–MS analysis, b TLC bioautography-based purification of compounds, c presence of different chemical groups in the partial purified ethyl acetate extract (PDB) and d depicting chemical structure of 2,4-Di-tert-butylphenol