Use of Reference Compounds in Antioxidant Activity Assessment

Abstract

The choice of reference compounds is examined as a "critical control point" of antioxidant activity assessment. Gallic, caffeic, sinapic, uric, and ascorbic acids, isoeugenol, and Trolox were tested using different redox (FRAP, Folin-Ciocalteu) and radical scavenging (DPPH*, ABTS*+, CBA, ORAC) assays. The ability to chelate transition metals was assessed to support some of the findings. Analytes were also tested in liposomes. On the basis of the findings, we do not recommend uric acid (due to solubility constrains) and ascorbic acid (due to fast degradation kinetics) as references. The behavior of the rest of the compounds could not always be attributed to typical structural characteristics. Selection of suitable reference compounds for in vitro antioxidant activity assays is not an easy task to achieve. The choice of reference compounds has to remain at the convenience of the researchers, with regard to the aim of the study.

Marker Constituents of the Natural Antioxidant Eucalyptus Leaf Extract for the Evaluation of Food Additives

“…34,35) Among polyphenols, including flavonol glycosides and hydrolyzable tannins characterized in the extract, bioactive oenothein B (2) might be a significant marker characteristic of the E. globulus leaf, because it is a rare natural product with a unique structure and can be detected easily without interference from other peaks on a reversed-phase HPLC chromatogram in a gradient mode with 5% AcOH and MeOH (Fig. 1).…”

Kinetic and Stoichiometric Evaluation of Free Radicals Scavengers Activities Based on Diphenyl-Picryl Hydrazyyl (Dpph) Consumption

“…It is then not expected a relationship between kinetic and stoichiometric evaluations. On the other hand, it is expected, and frequently found, good correlations between the number of hydroxyl groups in a compound and EC 50 values 16 . In complex mixtures it is frequently found a relationship between the amounts of total phenols titrated by Folin's method and the amount of DPPH molecules bleached 33,34 , in particular, with EC 50 values 26,35 .…”

“…In particular, it is widely employed the EC 50 parameter defined as the amount of antioxidants that, at a fixed time, bleaches half of the initial DPPH absorbance. In order to consider both the reactivity and stoichiometry of the tested sample it has been proposed an index that includes the EC 50 and the time required to reach the plateau at the EC 50 concentration 16,17 . In the present work we discuss the validity of the proposed methodologies, with particular emphasis on the information that can be derived from kinetic evaluations of the rate of DPPH bleaching and the stoichiometry of the process.…”

“…In the present work we discuss the validity of the proposed methodologies, with particular emphasis on the information that can be derived from kinetic evaluations of the rate of DPPH bleaching and the stoichiometry of the process. This is a conflicting subject and even there are not consensus regarding how to estimate the "final" DPPH concentration: 5 minutes 18 24 or reaching a plateau 25 or a steady state condition 26,27 .…”

Antioxidant Potential and Biochemical Analysis of Moringa oleifera Leaves

“…The ABTS •+ is decolorized by antioxidants according to their antioxidant content (Nenadis et al, 2007). The assay mixture contained reagent R1 (mixture of sodium acetate buffer solution and glacial acetic acid, pH5.8), sample extract and reagent R2 (mixture of sodium phosphate buffer solution, glacial acetic acid, hydrogen peroxide and ABTs).…”