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

XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society K N 04
Evaluation of antioxidant activity: a reagentless
electrochemical approach
Dulce Geraldo, Fátima Bento
Departament of Chemistry, Universidade do Minho, 4710-057 Braga
gdulce@quimica.uminho.pt
The growing interest in the study of the action of antioxidants in health and
biotechnology has led to the development of different analytical methods for the
evaluation of the antioxidant capacity of these compounds.
Cyclic voltammetry has been widely used in the analysis of samples containing mixtures
of antioxidants. The analysis of voltammograms gives qualitative information, which
relates to the identification of peaks, or waves resulting from overlapping voltammetric
peaks. This information is usually used to evaluate the power of the antioxidants present
in the sample. Quantitative information can be achieved by following two different
approaches, consisting in measuring the current intensity at a fixed potential, or the area
under the anodic scan of voltammograms. The values of current or area are converted to
relative values of antioxidant activity against a model antioxidant. Besides cyclic
voltammetry, electrochemical methods have been used as an alternative to optical
methods for monitoring the consumption of reactive species, such as the DPPH [1] . Other
studies reported the use of coulometric titration at constant current to generate reactive
species such as the cation radical ABTS [2] , Ce(IV) [3] , Cl 2
[4, 5] and Br 2 [5] . As the reactivity
of these species is different from that of naturally ROS involved in oxidative damage /
oxidative stress, the significance of these results is rather limited and may lead to an
underestimation or overestimation of the antioxidant activity according to the relative
value of the reduction potential of reactive species. Likewise, the difference between the
reduction potentials of the reactive species used in the various methods difficult the
establishment of a parallelism between the results from these methods.
The direct analysis of electron transfer with the antioxidants using controlled potential
exhaustive electrolysis can overcome these limitations.
In this work, we present a new analytical approach for evaluating the antioxidant
activity of chemical species in synthetic solutions or in natural systems, designed to
measure their reactivity against specific ROS (from the O 2 to the HO • ) under defined
experimental conditions (eg pH). The method is based on the response of antioxidants
during electrolysis conducted at a fixed potential, simulating an oxidative attack by a
natural ROS.
References
[1] Milardovic, S.; Ivekovic, D.; Grabaric B. S. Bioelectrochemistry, 2006, 68, 175.
[2] Alonso, A. M.; Dominguez, C.; Guillén D. A.; Barroso, C. G. J. Agric. Food Chem., 2002, 50,
3112.
[3] Ferreira, R. Q.; Avaca, L. A. Electroanalysis 2008, 20, 1323.
[4] Addullin, I. F.; Turova, E. N.; Ziyatdinova, G. K.; Budnikov, H. C. Journal of Analytical
Chemistry , 2002, 57, 730.
Talanta, 2006, 68, 800.
September, 811, 2010. ISEL - Lisbon 21