Evaluation of phytochemical composition and biological activities of ethanol extract of bark of Dialium ovoideum Thwaites

Abstract

The present study aimed to investigate the biological activities of the ethanol extract of the bark of Dialium ovoideum Thwaites (DOEB), which is an endemic plant of Sri Lanka with various medicinal values. A powdered bark sample was subjected to soxhlet extraction using ethanol followed by solvent evaporation to obtain the bark extract. The phytochemical screening performed on DOEB revealed the presence of phenols, flavonoids, tannins, saponins, terpenoids and steroids. The total phenolic and flavonoid contents of the DOEB were measured as 233.4±22.7 mg GAE/g and 198.1±24.5 mg QE/g, respectively. The antioxidant activity of DOEB showed an EC 50 of 68.5±6.3 μg/mL for the DPPH free radical scavenging assay and a significant (p<0.05) reductive potential compared to the ascorbic acid for the FRAP assay with a percentage reductive potential ranging from 5.7±0.8 to 79.2±2.2% across concentrations of 12.5 to 400 μg/mL. The modified L-DOPA method revealed the anti-tyrosinase activity of DOEB which is expressed as the IC50 of 1298.3±36.2 μg/mL. The human red blood cell stabilization assay by heat hemolysis resulted in an IC 50 of 425.7±9.3 μg/mL. The agar-well diffusion assay was conducted to assess the anti-microbial activities against the Staphylococus aureus, Escherichia coli, Klebsiella pneumoniae bacterial strains and the fungus, Candida albicans. The results exhibited that DOEB inhibited the growth of all three bacteria and fungi in different concentrations. Functional groups analysis of DOEB by FT-IR spectroscopy revealed the presence of alcohols, carboxylic acids, alkanes, alkenes, aliphatic esters, carbonyl and aromatic compounds. This study showed that DOEB has promising bioactivities based on the assays conducted which has a high potential to isolate bioactive compounds. Hence, DOEB may be employed as a prospective candidate in the food and pharmaceutical industries.