ASSAY OF ANTIOXIDANT POTENTIAL OF TWO ENDOPHYTIC FUNGI ISOLATED FROM THE LEAVES OF Psidium guajava

Abstract

Free radicals in humans are the leading causes of several diseases such as diabetes, cancer, etc. Antioxidants are an interesting topic today because of their ability to protect the human body from attacks by several diseases caused by free radical reactions. The search for chemical compounds that have the potential to be antioxidants from nature continues, and the use of endophytic fungi from P. guajava leaves as a source of antioxidant compounds has not been widely explored. As such, this study was conducted to investigate the antioxidant activity of the endophytic fungal extracts isolated from the leaves of P. guajava. Endophytic fungi Alternaria spp. (PG-2) and Rhizoctonia spp. (PG-10) isolated from healthy leaves of P. guajava were cultured in potato dextrose broth (PDB), tenellin production medium (TPM), and Rice medium (RM). The antioxidant activity of the crude extracts was observed using DPPH and ABTS assays. The result of the DPPH assay showed that the PG-2 extracts have the highest percentage inhibition (IC₅₀ values: PDB-PG-2 16.28; TPM-PG-2 20.59; RM-PG-2 21.36 g/ml) than the PG-10 extracts (IC₅₀ values: PDB-PG-10 118.22; TPM-PG-10 606.83; RM-PG-10 82.13 g/ml). The results were compared with three standards: ascorbic acid (IC₅₀: 1.41 g/ml); butylated hydroxytoluene (IC₅₀: 6.89 g/ml); and tannic acid (IC₅₀: 6.56 g/ml). The ABTS results obtained are expressed as Trolox equivalent antioxidant activity (TEAC) and Gallic acid equivalent (GAE). Both the extracts displayed a significant amount of Trolox and Gallic acid equivalence, which reflects their ability to donate hydrogen to scavenge radical formation. The results of the present study indicated that extracts with significant DPPH and ABTS activity are potential sources of natural antioxidants and pharmaceutical fungal-based products.