Phenolic contents, antioxidant and antibacterial activities of Hymenocardia acida

Abstract

This study investigates the antioxidant and antibacterial activities of aqueous and methanolic extracts from Hymenocardia acida Tul. (Hymenocardiaceae). The inhibition values of the extracts and quercetin were found to be very close, with no significant differences at a concentration of 0.05 mg mL⁻¹ in their ability to inhibit 1,1-diphenyl-2-picrylhydrazyl (DPPH). Total proanthocyanidins for both water and methanol extracts were 20.2 ± 0.01 and 30.6 ± 0.51 mg g⁻¹ (catechin equivalent) while the total phenol contents were 20.0 ± 0.52 and 35.6 ± 1.42 mg mL⁻¹ (tannic acid equivalent), respectively. Positive correlations R ² = 0.85, R ² = 0.94, R ² = 0.97 for DPPH, reducing power and 2′-azino-bis(3-ethylbenzo thiazoline)6-sulphonic acid (ABTS). Linear regression analysis also produced a high correlation coefficient with total proanthocyanidins (DPPH, R ² = 0.69; ABTS, R ² = 0.94). H. acida extracts showed low antibacterial activity (minimum inhibitory concentration (MIC) value ≥5.0 mg mL⁻¹) against gram negative bacteria but significantly (MIC value ≤2.5 mg mL⁻¹) inhibited the growth of the gram positive strains tested. Qualitative TLC of the extract was positive for flavonoids, phenols, steroids and triterpenoids.

The results of this study support the use of H. acida in traditional Nigerian medicine and show that the alcoholic extract of the leaves can be used as an easily accessible source of natural antioxidant and can be of assistance in some dermatological problems.

Keywords:

• Hymenocardia acida
• antioxidant activity
• antibacterial activity
• polyphenols

Acknowledgement

The authors are grateful to the NRF, South Africa and the University of Lagos, Nigeria, for their support.