title: Modified Folin-Ciocalteu antioxidant capacity assay for measuring lipophilic antioxidants.
abstract: The Folin-Ciocalteu (FC) method of performing a total phenolics assay, originally developed for protein determination, has recently evolved as a total antioxidant capacity assay but was found to be incapable of measuring lipophilic antioxidants due to the high affinity of the FC chromophore, that is, multivalent-charged phospho-tungsto-molybdate(V), toward water. Thus, the FC method was modified and standardized so as to enable simultaneous measurement of lipophilic and hydrophilic antioxidants in NaOH-added isobutanol-water medium. Optimal conditions were as follows: dilution ratio of aqueous FC reagent with iso-BuOH (1:2, v/v), final NaOH concentration of 3.5 × 10(-2) M, reaction time of 20 min, and maximum absorption wavelength of 665 nm. The modified procedure was successfully applied to the total antioxidant capacity assay of trolox, quercetin, ascorbic acid, gallic acid, catechin, caffeic acid, ferulic acid, rosmarinic acid, glutathione, and cysteine, as well as of lipophilic antioxidants such as α-tocopherol (vitamin E), butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquinone, lauryl gallate, and β-carotene. The modified FC method reliably quantified ascorbic acid, whereas the conventional method could not. The modified method was reproducible and additive in terms of total antioxidant capacity values of constituents of complex mixtures such as olive oil extract and herbal tea infusion. The trolox equivalent antioxidant capacities of the tested antioxidant compounds correlated well with those found by the Cupric Reducing Antioxidant Capacity reference method.
authors.affiliation: Department of Chemistry, Faculty of Science and Letters, Istanbul Technical University, Ayazaga Maslak, 34469 Istanbul, Turkey.
authors.forename: Kadriye Isil
authors.initials: KI
authors.lastname: Berker
authors.forename: F Ayca
authors.initials: FA
authors.lastname: Ozdemir Olgun
authors.forename: Dilek
authors.initials: D
authors.lastname: Ozyurt
authors.forename: Birsen
authors.initials: B
authors.lastname: Demirata
authors.forename: Resat
authors.initials: R
authors.lastname: Apak
mesh_terms: D000975:Antioxidants / Q000032:analysis*; D001205:Ascorbic Acid / Q000032:analysis; D001555:Benzene Derivatives / Q000032:analysis; D000440:Butanols; D005419:Flavonoids / Q000032:analysis; D007202:Indicators and Reagents; D008055:Lipids / Q000737:chemistry*; D008982:Molybdenum; D012972:Sodium Hydroxide; D017973:Tungsten Compounds; D014810:Vitamin E / Q000032:analysis; D024502:alpha-Tocopherol / Q000032:analysis; D019207:beta Carotene / Q000032:analysis
chemical_list: D000975:Antioxidants; D001555:Benzene Derivatives; D000440:Butanols; D005419:Flavonoids; C029556:Folin's phenol reagent; D007202:Indicators and Reagents; D008055:Lipids; D017973:Tungsten Compounds; D019207:beta Carotene; D014810:Vitamin E; D012972:Sodium Hydroxide; C040507:isobutyl alcohol; D008982:Molybdenum; D024502:alpha-Tocopherol; D001205:Ascorbic Acid