Turnera subulata is a medicinal plant used as an herbal remedy for coughs and bronchitis. Unlike two other members of the genus, Turnera diffusa and Turnera ulmifolia, which dominate the ethnopharmacological and pharmacological literature, very little is known about the bioactive properties of T. subulata. In this study, whole-plant profiling of the total phenolic and flavonoid contents as well as antioxidant capacity of T. subulata was accomplished by analysing the leaf, stem, root, fruit and flower extracts. Analyses of total phenolic and flavonoid contents, free radical scavenging activity and ferric reducing ability revealed that the leaf extract had the highest antioxidant potential. Comparison of total phenolic contents and antioxidant parameters between T. subulata leaf extract and the extracts of other medicinal plants also indicated T. subulata to be a rich source of antioxidant activities. Strong, positive correlations were found between total phenolic and flavonoid contents and three antioxidant parameters, namely Trolox equivalent antioxidant capacity (TEAC), ferric reducing antioxidant power (FRAP) and nitric oxide scavenging activity. Our results indicate that the total pool of phenolic compounds, including flavonoids, in the T. subulata extracts were capable of both scavenging free radicals and reducing oxidants.
Key words: Ferric reducing antioxidant power, flavonoids, free radical scavenging activities,nitric oxide, phenolics, trolox equivalent antioxidant capacity, Turnera subulata.
DPPH, 1,1-Diphenyl-2-picrylhydrazyl; ABTS, 2,2’-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid); FRAP, ferric reducing antioxidant power; TEAC, trolox equivalent antioxidant capacity.
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