In Vitro Antioxidant Activity of Methanolic Extracts of Leaves of Indigofera Indica and Stems of Stereospermum Suaveolens Grown in Sri Lanka

Abstract

Oxidative stress due to free radicals plays a fundamental role in pathogenesis of several human diseases. Accordingly, wide search is operative to discover novel and potent antioxidants to be used as prophylactics and therapeutics, and also in food and cosmeceutical industries .Thus, the aim of this study was to evaluate the antioxidant capacity of leaves of Indigofera indica ( Family : Leguminosae) and stems of Stereospermum suaveolens ( Family: Bignoniaceae) grown in Sri Lanka . Oven dried (at 40°C) , powdered leaves and air dried stems were extracted to methanol by cold extraction technique and their antioxidant activities were evaluated in vitro using four direct antioxidant assays [1,1- diphenyl-2-picrylhydrazyl (DPHH)], radical scavenging activity: 2,2'- azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging activity : ferric reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC) and two indirect antioxidant assays [ total polyphenolic content (TPC) and total flavonoid content (TFC)]. The results showed that both extracts exhibit moderate antioxidant activity [ DPPH assay , leaves Vs stem : 11.53 ± 0.50 Vs 13.46 ± 0.22 mg Trolox equivalent /g ; ABTS assay , leaves Vs stem 156.66 ± 12.87 Vs 146.14 ± 3.15 mg Trolox equivalent /g , FRAP assay , leaves Vs stem 11.76 ± 3.93 Vs 13.59 ± 4.36 mg Trolox equivalent /g ; ORAC assay , leaves Vs stem 198.83 ± 6.09 Vs 209.61 ± 16.10 mg Trolox equivalents /g ; TPC assay , leaves Vs stem: 193.45 ± 9.60 Vs 102.26 ± 6.04 mg Gallic acid equivalents /g, and TFC assay , leaves Vs stem : 22.56 ± 0.42 Vs 0.12 ± 0.04 mg Quercetin equivalents /g]. Further, the radical scavenging activities determined by DPPH and ABTS assays were dose dependent. These results establish, for the first time, that leaves of I.indica and stem of S.suaveolens grown in Sri Lanka are good source of natural antioxidants that may be effective against oxidative stress induced pathophysiology of several diseases