Antioxidative activity of the crude extract of lignan glycosides from unroasted Burma black sesame meal

Abstract

Sesame seed contains lignans and lignan glycosides. The antioxidative activity of the crude extract of lignan glycosides obtained from unroasted defatted black sesame seeds was investigated in this study. The components responsible for the antioxidative activity were also studied. The unroasted black sesame seeds, after defatted with n-hexane, were extracted with 80% methanolic solution to prepare for the crude extract of lignan glycosides. After chromatographic separation of this crude extract with octadecylsilane (ODS) column (2.5 cm i.d.×100 cm), four fractions (Fr1, Fr2, Fr3, Fr4) of the crude extract were obtained from the eluents of 25, 50, 75% aqueous methanolic solution and 100% methanol, respectively. Among them, Fr2 and Fr3 showed better antioxidative activity by 2,2-Diphenyl-1-picrylhydrazyl hydrate (DPPH) antioxidative assay. These two fractions were further purified by preparative HPLC (Hyperprep 100 C18 column; 20 mm i.d.×250 mm) and the main constituents were found to be lignan glycosides and some unknown brown materials. It was interesting to find that the brown materials (in Fr2) exhibited exceptional DPPH free radical scavenging effect, whereas the identified sesaminol triglucoside in Fr2 and sesaminol diglucoside in Fr3 possess no such activity. Using Cu +2-induced oxidation of human low-density lipoprotein (LDL) for the antioxidative assay, similar results were observed. Seaminol triglucoside and sesaminol diglucoside showed no effect on the extension of lag phase, while the brown materials had excellent inhibitory effect on the oxidation of LDL. Furthermore, natural antioxidants such as γ-tocopherol, sesamol and sesaminol were not detected in the crude extract of lignan glycosides. Our findings suggest that the brown materials present in Fr2 had a significant contribution to the antioxidative activity of the crude extract of lignan glycosides. Identification of the responsible components is underway.