title: Effect of pH and metal ions on DPPH radical scavenging activity of tea.
abstract: The 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assay is commonly applied for the estimation of antioxidant activity of plant extracts. This article discusses the effect of a sample pH and the presence of metal ions on the results obtained using DPPH method for several tea infusions. Higher radical quenching was observed in less acidic media. The impact of metal ions depends of the types of metal ion and its concentration. Quercetin and epigallocatechin gallate were less efficient in the reaction with DPPH in the presence of Al(III). Desalting process using cation-exchange resin Dowex 50Wx8 decreased the content of metal ions in all studied tea infusions. The DPPH scavenging activity of the effluents after this process were higher than those of the primary extracts and this may be related to the actual antioxidant capacity of these samples.
authors.affiliation: Department of Chemistry, University of Warsaw , Warsaw , Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Pękal
authors.forename: Krystyna
authors.initials: K
authors.lastname: Pyrzynska
mesh_terms: D000535:Aluminum / Q000737:chemistry; D001713:Biphenyl Compounds / Q000737:chemistry*; D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D016166:Free Radical Scavengers / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010851:Picrates / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry; D013662:Tea / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry
chemical_list: D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D010851:Picrates; D010936:Plant Extracts; D013662:Tea; D003300:Copper; D002392:Catechin; C045651:epigallocatechin gallate; D000535:Aluminum; C004931:1,1-diphenyl-2-picrylhydrazyl; D015032:Zinc
keywords: DPPH assay; metal chelation; phenolic compounds; resin purification; tea