This study investigated the in vitro antioxidant activity and phenolic content of aqueous and ethanol extracts of Alstonia boonei and Eupatorium odoratum leaves. Total phenol, flavonoid and flavonol content of the extracts were estimated to determine the levels of phenolics in the extracts. The antioxidant capacity of the extracts were assessed through diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging activity, ferric reducing antioxidant power (FRAP) and reducing power (RP). The results revealed that the DPPH radical scavenging ability of aqueous extract of E. odoratum (with IC50 = 0.07± 0.003mg/ml) compares favourably with that of the standard ascorbic acid (IC50 = 0.06 ± 0.01 mg/ml). There was a dose-dependent increase in FRAP and RP capacity in all the extracts. The ethanol extract of E. odoratum had the highest FRAP while the aqueous extract of A. boonei showed the highest RP ability when compared with the other extracts. However, flavonol content was highest in the aqueous extract of E. odoratum followed by ethanol extract of A. boonei. The phenolic and flavonoid contents of extracts of E. odoratum were higher than that of A. boonei extracts. This study, therefore, reveals that aqueous extract of A. boonei and ethanol extract of E. odoratum leaf are more effective free radical scavengers and antioxidants relative to the other extract forms. These findings support the use of these extracts as potential sources of natural antioxidants.
Key words: Alstonia boonei, Eupatorium odoratum, phenolics, antioxidant
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