title: Antioxidant activity of Sempervivum tectorum and its components.
abstract: The antioxidant properties of components of leaf extracts of the evergreen plant, Sempervivum tectorum (ST), have been evaluated using UV irradiated liposomal systems containing the spin trap 5-(diethoxyphosphoryl)-5-methyl-pyrroline-N-oxide. Decreases in free radical activity in the liposomal systems as measured by electron paramagnetic resonance (EPR) spectroscopy demonstrate that the lipophilic ST juice components, kaempferol (KA) and kaempferol-3-glucoside (KG) contribute significantly to the antioxidant properties of the juice. EPR spectral simulation established the presence of oxygen and carbon centered free radical adducts. The mixtures with low pH, citric and malic acid, and ST juice reveal increased EPR signals from oxygen centered radicals in comparison to the control, pointing to the important role of pH in oxygen radical formation. Parallel assays that measured thiobarbituric acid related substances confirm the antioxidant effects of KA and KG and explain the results of spin trapping experiments complicated by low pH's.
authors.affiliation: EPR Center, J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Marjeta
authors.initials: M
authors.lastname: Sentjurc
authors.forename: Marjana
authors.initials: M
authors.lastname: Nemec
authors.forename: Henry D
authors.initials: HD
authors.lastname: Connor
authors.forename: Veronika
authors.initials: V
authors.lastname: Abram
mesh_terms: D029627:Crassulaceae / Q000737:chemistry*; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism*; D005609:Free Radicals; D006863:Hydrogen-Ion Concentration; D044949:Kaempferols; D008081:Liposomes; D010084:Oxidation-Reduction; D010936:Plant Extracts / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry; D013113:Spin Labels; D019097:Spin Trapping; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis; D014466:Ultraviolet Rays
chemical_list: D003497:Cyclic N-Oxides; D005419:Flavonoids; D005609:Free Radicals; D044949:Kaempferols; D008081:Liposomes; D010936:Plant Extracts; D013113:Spin Labels; D017392:Thiobarbituric Acid Reactive Substances; C098505:5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide; C006552:kaempferol