Antioxidant activity applying an improved ABTS radical cation decolorization assay.

Free radicals, metals and antioxidants in oxidative stress-induced cancer

This review summarizes the multifaceted aspects of antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Depending upon the reactions involved, these assays can roughly be classified into two types:  assays based on hydrogen atom transfer (HAT) reactions and assays based on electron transfer (ET). The majority of HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. These assays include inhibition of induced low-density lipoprotein autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced. The degree of color change is correlated with the sample's antioxidant concentrations. ET-based assays include th...

The Chemistry behind Antioxidant Capacity Assays

Publisher Summary This chapter discusses the role of free radicals and catalytic metal ions in human disease. The importance of transition metal ions in mediating oxidant damage naturally leads to the question as to what forms of such ions might be available to catalyze radical reactions in vivo . The chapter discusses the metabolism of transition metals, such as iron and copper. It also discusses the chelation therapy that is an approach to site-specific antioxidant protection. The detection and measurement of lipid peroxidation is the evidence most frequently cited to support the involvement of free radical reactions in toxicology and in human disease. A wide range of techniques is available to measure the rate of this process, but none is applicable to all circumstances. The two most popular are the measurement of diene conjugation and the thiobarbituric acid (TBA) test, but they are both subject to pitfalls, especially when applied to human samples. The chapter also discusses the essential principles of the peroxidation process. When discussing lipid peroxidation, it is essential to use clear terminology for the sequence of events involved; an imprecise use of terms such as initiation has caused considerable confusion in the literature. In a completely peroxide-free lipid system, first chain initiation of a peroxidation sequence in a membrane or polyunsaturated fatty acid refers to the attack of any species that has sufficient reactivity to abstract a hydrogen atom from a methylene group.

Role of free radicals and catalytic metal ions in human disease: an overview.

Methods available for the measurement of antioxidant capacity are reviewed, presenting the general chemistry underlying the assays, the types of molecules detected, and the most important advantages and shortcomings of each method. This overview provides a basis and rationale for developing standardized antioxidant capacity methods for the food, nutraceutical, and dietary supplement industries. From evaluation of data presented at the First International Congress on Antioxidant Methods in 2004 and in the literature, as well as consideration of potential end uses of antioxidants, it is proposed that procedures and applications for three assays be considered for standardization: the oxygen radical absorbance capacity (ORAC) assay, the Folin-Ciocalteu method, and possibly the Trolox equivalent antioxidant capacity (TEAC) assay. ORAC represent a hydrogen atom transfer (HAT) reaction mechanism, which is most relevant to human biology. The Folin-Ciocalteu method is an electron transfer (ET) based assay and gives reducing capacity, which has normally been expressed as phenolic contents. The TEAC assay represents a second ET-based method. Other assays may need to be considered in the future as more is learned about some of the other radical sources and their importance to human biology.

https://faculty.missouri.edu/~glaserr/3700s14/Antioxidant-Capacity_jf0502698.pdf

Standardized Methods for the Determination of Antioxidant Capacity and Phenolics in Foods and Dietary Supplements

The relative contributions of vitamin E, urate, ascorbate and proteins to the total peroxyl radical-trapping antioxidant activity of human blood plasma.

Is vitamin E the only lipid-soluble, chain-breaking antioxidant in human blood plasma and erythrocyte membranes?

On mesure les constantes de vitesse de l'elimination de l'hydrogene atomique par les radicaux peroxyles de l'α-tocopherol et de 35 phenols structuralement apparentes. Les mesures sont faites par la methode de l'autooxydation inhibee du styrene

Autoxidation of biological molecules. 4. Maximizing the antioxidant activity of phenols

Article de synthese sur la vitamine E. Etude de son activite antioxydante sous la forme de α-tocopherol et de son role dans la peroxidation des lipides, sur les radicaux libres. Cinetique et mecanismes d'action dans les organes et les tissus; forme active. Pour mesurer l'absorption et le transport de la vitamine E, utilisation d'un isotope stable marque et analyse par chromatographie gazeuse et spectrometrie de masse. Mesure de sa biodisponibilite. Transport de la vitamine E et lipoproteine chez l'homme

Vitamin E: Antioxidant Activity, Biokinetics, and Bioavailability

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2885%2981208-4

Quantitative measurement of the total, peroxyl radical-trapping antioxidant capability of human blood plasma by controlled peroxidation. The important contribution made by plasma proteins.

Graham W. Burton

Papers

The relative contributions of vitamin E, urate, ascorbate and proteins to the total peroxyl radical-trapping antioxidant activity of human blood plasma.

Is vitamin E the only lipid-soluble, chain-breaking antioxidant in human blood plasma and erythrocyte membranes?

Autoxidation of biological molecules. 4. Maximizing the antioxidant activity of phenols

Vitamin E: Antioxidant Activity, Biokinetics, and Bioavailability

Quantitative measurement of the total, peroxyl radical-trapping antioxidant capability of human blood plasma by controlled peroxidation. The important contribution made by plasma proteins.