Phenolic content, antioxidant and antibacterial activities of Hymenocardia acida

The antioxidant and antibacterial activities of the aqueous and methanolic extracts obtained from Hymenocardia acida Tul., Hymenocardiaceae (Euphorbiaceae), were investigated in this study. The inhibition values of extracts and quercetin were found to be very close with no significant difference in the antioxidant activity at 0.05mg/ml concentration evaluated by DPPH method. Total proanthocyanidins for both water and methanol extracts were 20.22±0.01 and 30.62±0.51mg/g (catechin equivalent) while the total phenol contents were 20.0±0.5 and 35.6±1.4mg/ml (tannic acid equivalent) respectively. Total flavonoid 1.6±0.1 and 5.4±0.2 for aqueous and methanolic extracts respectively. In the DPPH assay, antioxidant activity of the samples was in the order of quercetin > methanol extract > water extract. At 0.02mg/ml, quercetin, methanol and water extracts of H. acida exhibited 93.4, 85.5 and 55.4% scavenging activity, respectively. There was no significant difference (P<0.01) in scavenging activity between the extracts and quercetin at 0.05mg/ml. Activity of quercetin was found to be significantly more pronounced than ascorbic acid, methanol and water extracts. These results revealed that extracts of H. acida were electron donors and could react with free radicals, converting them to more stable products and terminating the radical chain reaction. The antioxidant activity trend obtained in this result corresponds directly with the content of total phenolics in the extracts, with a correlation coefficient of R² =0.85; R²=0.94; R²=0.97 for DPPH, reducing power and ABTS respectively. Linear regression analysis also produced a high correlation coefficient with total proanthocyanidins (DPPH, R²=0.69; ABTS, R² =0.94).

H. acida extracts showed low antibacterial activity (MIC value ≥5.0mg/ml) against Gram-negative bacteria but significantly (MIC value ≤2.5mg/ml) inhibited the growth of the Gram-pos strains tested.

Acknowledgements: NRF, South Africa, and University of Lagos, Nigeria.