title: Antioxidant oligomeric proanthocyanidins from sea buckthorn (Hippophae rhamnoides) Pomace.
abstract: After flavonol glycosides, monomeric flavan-3-ols, and dimeric and trimeric proanthocyanidins were fractionated from an extract of sea buckthorn (Hippophae rhamnoides) pomace by Sephadex LH-20 gel chromatography, oligomeric proanthocyanidins were eluted. The oligomeric fraction accounted for 84% of the total proanthocyanidins and 75% of the total antioxidant activity of the sea buckthorn pomace extract. To elucidate the structure of the oligomeric fraction, it was depolymerized by acid catalysis in the presence of phloroglucinol. The structure of the resulting flavan-3-ol monomers and flavan-3-ol-phloroglucinol adducts was determined by electrospray ionization mass spectrometry (ESI-MS) and (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy. Quantitative high-performance liquid chromatography investigations demonstrated (+)-gallocatechin as the predominating subunit in the oligomeric fraction. This observation was confirmed by ESI-MS, matrix-assisted laser desorption/ionization mass spectrometry, and (13)C NMR spectroscopy. The results showed that the majority of the flavan-3-ol subunits possessed a 2,3-trans configuration. The oligomers consisted mainly of prodelphinidin subunits whereas procyanidins were present in smaller amounts, indicating a very uncommon composition of the sea buckthorn proanthocyanidins. The mean degree of polymerization of the oligomeric proanthocyanidins was between 6 and 9.
authors.affiliation: Institut für Lebensmitteltechnologie und Lebensmittelchemie, Technische Universität Berlin, Gustav-Meyer-Allee 25, D-13355 Berlin, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rösch
authors.forename: Clemens
authors.initials: C
authors.lastname: Mügge
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Fogliano
authors.forename: Lothar W
authors.initials: LW
authors.lastname: Kroh
mesh_terms: D000975:Antioxidants / Q000302:isolation & purification*; D044948:Flavonols / Q000737:chemistry / Q000302:isolation & purification; D031281:Hippophae / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D044945:Proanthocyanidins / Q000737:chemistry / Q000302:isolation & purification*; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000975:Antioxidants; D044948:Flavonols; D044945:Proanthocyanidins