title: Novel EPR characterization of the antioxidant activity of tea leaves.
abstract: Electron paramagnetic resonance (EPR) spectroscopy is utilized to investigate several categories of green and black tea: Twining green tea (TGT), Chinese green tea (CGT), Red-labels black tea (RBT). Basically, two EPR signals from all the studied samples are observed: One of them is a very weak sharp EPR signal with deltaHpp approximately 10 G and g-factor = 2.00023 superimposed on the other broad signal with deltaHpp approximately 550 G and g-factor = 2.02489. The broad signal is a characteristic one of manganese(II) complex, while the sharp signal is related to a stable radical of aromatic origin exist in a powder condition. The feature of the manganese EPR signal is attributed to manganese(II) complex and reflected the molecular behavior of Mn(II) in the protein system of the natural leaves. The sharp signal, which is most probably due to a semiquinones radicals, is observed at room temperature and its intensity is remarkably affected by photo degradation of the studied samples. The intensity of manganese(II) EPR signal is found to be related to ageing and disintegration of the tea leaves. Moreover, direct relation between the relative intensity of the semiquinones radical signal and antioxidant activity of the studied samples was also correlated.
authors: Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. mamorsy@kfupm.edu.sa
authors: M A
authors: MA
authors: Morsy
authors: M M
authors: MM
authors: Khaled
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008027:Light; D010100:Oxygen / Q000378:metabolism; D010936:Plant Extracts / Q000032:analysis*; D013662:Tea / Q000737:chemistry*; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D000975:Antioxidants; D010936:Plant Extracts; D013662:Tea; D010100:Oxygen