Objective: Reactive oxygen has been implicated in degenerative diseases and medicinal activity of most herbs has been attributed to their ability to scavenge free radicals.
Methods: Free radical scavenging and antioxidant activities of ethanolic extracts from the leaves of varieties of medicinal plants, namely Azadiratcha indica, Mangifera indica, Moringa oleifera, Psidium guajava, Terminalia catappa, Anacardiaceae occidentale, Cassia siamae, Chromolaena odorata, Telfaira occidentalis and Paraquetina nigresiens were evaluated. Reducing power, DPPH scavenging, hydroxyl radical scavenging and ferrous ion chelating activities, phenolic, flavonoid and vitamin C contents were determined.
Results: C.siamae had excellent DPPH scavenging activity while P.guajava presented the lowest value. T.catappa had peak hydroxyl radical scavenging activity whereas T.occidentalis had the least capacity. C.siamae had the highest total phenolic and flavonoid contents while P.guajava and P.nigresiens showed the lowest phenol and flavonoid values. C.siamae also exhibited the highest reducing power activity whereas P.nigresiens had the least value. P.nigresiens had excellent ferrous iron chelating capacity while C.odorata had only poor activity. The total phenolic and flavonoid contents were highly correlated with the DPPH scavenging and reducing power activities, respectively. M.oleifera had the highest vitamin C content while P.guajava was the least..
Conclusion: Different values were obtained for each parameter for the medicinal leaves and free radical scavenging activity could be attributed to total phenolic and total flavonoid content. Among the plants tested, Cassia siamae leaf extract consistently exhibited the highest antioxidant activity and seems to be a promising source of natural antioxidants.
Key words: Antioxidant activity; Flavonoids; Medicinal leaves; Phenolics; Vitamin C