In vitro studies on antioxidant activity of lignans isolated from sesame cake extract

Abstract

The antioxidant activity of compounds isolated from a methanolic extract of commercial sesame cake was studied using a peroxidation model and a radical-scavenging method. Pure compounds were isolated from the extract by preparative high-performance liquid chromatography (HPLC) and identified and confirmed as sesamol, sesamin, sesamolin, sesaminol diglucoside and sesaminol triglucoside by HPLC, infrared, nuclear magnetic resonance and mass spectrometry. When the rate of inhibition of lipid peroxidation and the superoxide radical-scavenging power of the individual compounds were evaluated, the compounds showed antioxidant activity to different extents. The antioxidant activity of compounds by the beta-carotene-bleaching assay followed the order sesamol > sesamolin > sesamin > butylated hydroxytoluene (BHT) > sesaminol triglucoside > sesaminol diglucoside. By the thiocyanate method the inhibition of finoleic acid peroxidation shown by sesamol, sesamin, sesamolin, sesaminol triglucoside, sesaminol diglucoside and BHT at 200mgl(-1) was 77, 60, 69, 32, 25 and 49% respectively. A concentration-dependent superoxide-scavenging effect was also shown by these compounds. Sesamolin had an appreciable effect at 300 and 500mgl(-1), while the other compounds were more effective at 100mgl(-1). The study also established the occurrence of sesamol in the methanolic extract of defatted sesame cake for the first time.