title: Black sesame pigment: DPPH assay-guided purification, antioxidant/antinitrosating properties, and identification of a degradative structural marker.
abstract: An improved purification 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% reduction at 0.5 mg/mL), good ferric ion-reducing capacity (61 μM Trolox equivalent concentration 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 polymerization of coniferyl alcohol (polyconiferyl alcohol, PCA), the putative biosynthetic precursor to the sesame pigment, was characterized as a reference standard. FT IR spectra of the purified sesame pigment and PCA supported the structural similarity. HPLC analysis of degradation products by alkaline 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 degradation of PCA. A positive correlation between VA yields and DPPH activity was determined in samples of different purities. It is suggested that VA is a structural marker of black sesame pigment, confirming the biosynthetic origin from coniferyl alcohol and pointing to the o-methoxyphenol motif as the key factor accounting for the potent antioxidant properties of the pigment.
authors.affiliation: Department of Organic Chemistry and Biochemistry, University of Naples Federico II , Via Cintia 4, I-80126 Naples, Italy. panzella@unina.it
authors.forename: Lucia
authors.initials: L
authors.lastname: Panzella
authors.forename: Thomas
authors.initials: T
authors.lastname: Eidenberger
authors.forename: Alessandra
authors.initials: A
authors.lastname: Napolitano
authors.forename: Marco
authors.initials: M
authors.lastname: d'Ischia
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000302:isolation & purification; D001713:Biphenyl Compounds / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D015394:Molecular Structure; D015538:Nitrosation / Q000187:drug effects; D010084:Oxidation-Reduction; D010636:Phenols / Q000737:chemistry; D010851:Picrates / Q000737:chemistry*; D010860:Pigments, Biological / Q000737:chemistry* / Q000302:isolation & purification; D010936:Plant Extracts / Q000737:chemistry* / Q000302:isolation & purification; D012639:Seeds / Q000737:chemistry*; D031685:Sesamum / Q000737:chemistry*; D014641:Vanillic Acid / Q000737:chemistry / Q000302:isolation & purification
chemical_list: D000975:Antioxidants; D001713:Biphenyl Compounds; D005609:Free Radicals; D010636:Phenols; D010851:Picrates; D010860:Pigments, Biological; D010936:Plant Extracts; C004931:1,1-diphenyl-2-picrylhydrazyl; C010559:coniferyl alcohol; D014641:Vanillic Acid