title: The evaluation of reduction of Fe(III) in 3-hydroxy-4-nitroso-2,7-naphthalene disulphonic medium as an alternative ferric reducing activity power assay.
abstract: BACKGROUND
  The growing interest in determination of anti-oxidant capacity through non-labour, effective and less costly methods encouraged the development of the spectrophotometric procedure presented in this study.
  
  
  OBJECTIVE
  To investigate the reduction reaction of Fe(III) in 3-hydroxy-4-nitroso-2,7-naphthalenedisulphonic anion (NRS) medium as an alternative ferric reducing activity power (FRAP) assay for determining the total reduction capacity (RC).
  
  
  METHODS
  The absorbance values at 730 nm were used to determine the RC of aqueous extracts of nine Brazilian plants. The results were compared with the values obtained with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and with the total polyphenol content (TPC). The RCs of phenolic derivatives, flavonoids, amino acids and other anti-oxidant compounds were determined.
  
  
  RESULTS
  Paired t-test with RC values obtained with both assays (proposed FRAP and DPPH) showed no statistically significant difference. In addition, the RC values from the proposed FRAP assay are proportional to those found with TPC values (r =0.916). In addition, the conditional reduction potential of the Fe(III)/Fe(II) couple (0.685 V vs NHE (normal hydrogen electrode)) and the molar absorptivities at 730 nm of the Fe(NRS)(3)(3-) and Fe(NRS)(3)(4-) complexes (1.88 × 10(3) and 1.77 × 10(4)  L/cm × mol, respectively) were calculated because these values were not available.
  
  
  CONCLUSIONS
  The proposed assay is adequate for determination of the RC of plant extracts, and the results infer that other samples derived from plants (e.g. beers and wines) and even biological samples (e.g. serum and urine) also could be analysed.
authors.affiliation: Faculdade de Medicina da Fundação do ABC, CEPES (Centro de Estudos, Pesquisa, Prevenção e Tratamento em Saúde), CEP- 09060-650, Santo André, SP, Brazil.
authors.forename: Maryane Woth
authors.initials: MW
authors.lastname: de Souza
authors.forename: Horacio Dorigan
authors.initials: HD
authors.lastname: Moya
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000975:Antioxidants / Q000032:analysis; D001713:Biphenyl Compounds / Q000737:chemistry; D001938:Brazil; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D005290:Ferric Compounds / Q000737:chemistry*; D005419:Flavonoids / Q000032:analysis; D009281:Naphthalenes / Q000032:analysis; D010084:Oxidation-Reduction; D010851:Picrates / Q000737:chemistry; D010936:Plant Extracts / Q000737:chemistry* / Q000302:isolation & purification; D010944:Plants / Q000737:chemistry*; D059808:Polyphenols / Q000032:analysis; D013053:Spectrophotometry / Q000379:methods
chemical_list: D000596:Amino Acids; D000975:Antioxidants; D001713:Biphenyl Compounds; D005290:Ferric Compounds; D005419:Flavonoids; D009281:Naphthalenes; D010851:Picrates; D010936:Plant Extracts; D059808:Polyphenols; C031721:naphthalene; C004931:1,1-diphenyl-2-picrylhydrazyl
keywords: 3-hydroxy-4-nitroso-2,7-naphthalenedisulphonic acid, Fe(III); FRAP assay; medicinal Brazilian plants; total reduction capacity