Black Sesame Pigment: DPPH Assay-Guided Purification, Antioxidant/Antinitrosating Properties, and Identification of a Degradative Structural Marker

An improved purifn. procedure leading to black sesame (Sesamum Indicum L.) pigment was developed involving fat removal by treatment of ground black sesame seeds with dichloromethane followed by an optimized hydrolytic protocol with 6 M HCl, at 100 °C, overnight. The black pigment thus obtained displayed good antioxidant efficiency by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical assay (82% redn. at 0.5 mg/mL), good ferric ion-reducing capacity (61 ??M Trolox equiv. concn. at 0.5 mg/mL), and potent antinitrosating properties (74% inhibition of 2,3-diaminonaphthalene (DAN) nitrosation at gastric pH at 2.5 mg/mL). A synthetic pigment obtained by oxidative polymn. of coniferyl alc. (polyconiferyl alc., PCA), the putative biosynthetic precursor to the sesame pigment, was characterized as a ref. std. FT IR spectra of the purified sesame pigment and PCA supported the structural similarity. HPLC anal. of degrdn. products by alk. hydrogen peroxide of purified black sesame pigment showed the formation of vanillic acid (VA) as the main isolable fragment. Similar yields of VA were obtained by degrdn. of PCA. A pos. correlation between VA yields and DPPH activity was detd. in samples of different purities. It is suggested that VA is a structural marker of black sesame pigment, confirming the biosynthetic origin from coniferyl alc. and pointing to the o-methoxyphenol motif as the key factor accounting for the potent antioxidant properties of the pigment.