Comparison of antioxidant activity of bark of seven species of genera Frangula Mill. and Rhamnus L. (Rhamnaceae)

Abstract

Plants of genus Rhamnus L. and Frangula Mill. are frequently used in phytomedicine, mainly for their purgative properties [1]. The purpose of this study was to compare radical scavenging and antioxidant activity of bark of two Frangula Mill. (F. alnus L., F. rupestris (Scop.) Schur) and five Rhamnus (R. alaternus L., R. cathartica L., R. intermedia Steud. et Hohst., R. orbiculata Bornm., R. saxatilis Jacq.) species which grow in Croatia. Methanolic extracts of barks were prepared by ultrasonication. Content of total phenols were determined by using Folin Ciocalteu reagent. Antioxidant activity was investigated using following methods: radical scavenging activity of 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free-radical, reducing power, chelating activity and beta-carotene-linoleic acid assay. The greatest content of phenolic substances was found in extract of F. alnus (63 mg/g) while the phenolic content in the other extracts was almost twice lower (between 38 and 23 mg/g). The extracts demonstrated notable antioxidant activity in all the assays. The strongest chelator of Fe2+ ions was the extract of R. orbiculata. The extract of F. alnus was the most active in all the remaining assays. The activity of F. alnus extract in beta-carotene-linoleic acid assay was significantly higher than the activity of butylated hydroxyanisole (BHA) (ANOVA, p<0.05). Antioxidant activity in all the tests correlated well with content of total phenols (r2 was between 0.46 and 0.79, p<0.001). This suggests that phenolic compounds are main antioxidant substances in bark of investigated Frangula and Rhamnus species.