XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PB 05
Evaluation of gallic acid antioxidant activity based on its
extensive oxidation promoted by electrochemical methods
Raquel Oliveira, Juliana Marques, Fátima Bento, Dulce Geraldo, Paula
Bettencourt
Departament of Chemistry, Universidade do Minho, 4710-057
juliana.g.marques@hotmail.com
Cellular oxidative stress and oxidative degradation of foods are associated to the
occurrence of oxidative processes on a large scale involving reactive oxygen species
(ROS) such as O 2 , H 2 O 2 , O 2 •- and HO • . The promoted oxidation reactions may involve
free radicals that start chain reactions, causing large scale destruction of molecules and
biological systems (such as cells). The antioxidants action on the prevention of oxidative
damage is widely recognized and is associated to their ability to remove free radicals
and to inhibit the oxidation of other molecules through their own oxidation.
The identification of the activity of recognized antioxidants or of new molecules is
carried out by different methods, mostly chemical, which allow characterizing the
reactions of these compounds with various reactive species. The use of synthetic radicals
such as ABTS •+ (2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate)), DPPH • (2,2-
diphenyl-1-picrylhydrazyl) or DMPD •+ (N,N-dimethyl-p-phenylenediamine) is common
in chemical assays despite their lack of meaning in biological or chemical natural
samples. The generation of ROS is of fundamental importance in order to carry out
relevant activity tests.
Electrochemical methods, such as cyclic voltammetry have been extensively used to
characterize antioxidants, through the estimation of their standard reduction potentials,
E 0 . Despite the importance of this thermodynamic parameter, the kinetic
characterization of reactions of antioxidants is crucial because it determines their ability
to respond in time.
In this paper, we present a study on the gallic acid response to a large scale oxidative
attack promoted by electrochemical means. By adjusting the anode potential, the assay
enables to test the antioxidant behavior against oxidants of different strength. This is an
advantage toward chemical assays based on a chemical oxidant characterized by a fixed
redox potential, E 0 . Another advantage of the electrochemical oxidative attack is the
ease monitoring of the oxidation reaction rate, which is assessed directly from the
current, in opposition to the chemical assays that require the direct monitoring of the
oxidant or of a probe in a competitive assay.
Acknowledgments: Fundação para a Ciência e a Tecnologia (SFRH/BD/64189/2009).
September, 811, 2010. ISEL - Lisbon 71