Comparative Analysis of Phytochemical Constituents and Antioxidant Properties of Aqueous and Ethanol Extracts of Alstonia boonei Stem-Bark

Abstract

The plant Alstonia boonei is extensively used in traditional medicine because of its therapeutic properties. Over the years, researchers have been looking for the active medicinal agents in different plant species and as such, the type of extraction solvent plays a major role. This study aim to investigate the comparative analysis of phytochemical constituents and antioxidant properties of aqueous and ethanol extracts of A. boonei stem-bark. The stem-bark of A. boonei was collected, dried, pulverized and extracted with ethanol and distilled water using maceration method. The extract was concentrated in a temperature regulated water bath set at 45oC. Qualitative and quantitative phytochemical analysis was carried out in both extracts. Both extracts was also subjected to various antioxidant analytical procedures such as free radical scavenging capacity against 1, 1-diphenyl-2-picrylhydrazyl (DPPH), reducing power, and ferric reducing antioxidant power (FRAP) to determine antioxidant properties. The qualitative phytochemical analysis of both extracts revealed the presence of flavonoids, cardiac glycoside, terpenoids, alkaloids and saponins. However, quantitative studies revealed that proanthocyanidin, flavonoids and total phenol were significantly higher in ethanol extract compared to aqueous extract (p < 0.05). Both extracts exhibited antioxidant activities compared to reference antioxidant (Ascorbic acid). However, the reducing power of the aqueous extract was significantly higher than that of the ethanol extract.This result indicates that aqueous extract of A. booneistem-bark had lower phytochemical constituents but higher antioxidant activity compared to ethanol extract. The result of this study revealed that ethanol may be a better solvent for phytochemical extraction of A. boonei stem-bark.