Comparative study of different methodologies for the determination the antioxidant activity of Venezuelan propolis

Abstract

Propolis is a complex resinous substance produced by bees. Its physical and chemical composition vary according to the flora near the apiary and its geographical origin. Seven propolis samples, collected from different productive areas from Venezuela were selected to characterize their main antioxidant properties taking as reference well recognized samples from Argentina and Brazil. Total phenolic compound and flavonoid contents were determined by Folin-Ciocalteu and AlCl3 methods, respectively. The antiradical activity (ARA) was evaluated by bleaching techniques using both the 1,1-diphenyl-2-picrylhydrazyl (DPPH[rad]) radical and 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical (ABTS[rad]+). Ferric ion reducing power (FRAP) and the antioxidant activity (AAO) by the β-carotene bleaching method induced by lipoxygenase were also determined. The electrochemical behavior of the ethanolic extracts was evaluated by cyclic voltammetry. The values obtained using the different methodologies showed variable results among different samples even being from the same provenance. Phenolic contents of Venezuelan propolis reached values in a wide range between 19.1 and 107 mg GAE/g. Flavonoid contents varied between 2.6 and 8.5 mg QE/g. Samples from Bolivar and Miranda did not differ statistically each other in their properties, although, can be distinguished from other provenances as Argentinean and Brazilian. Regarding to the electrochemical behavior, half of the samples showed two oxidation peaks. The remaining ones had correlation between the IC50 from O2[rad]− and DPPH[rad] scavenging assays. The highest correlations were found between FRAP and IC50 (O2[rad]−) (R = 0.70); IC50 (DPPH) (R = 0.89) and phenolic contents (R = 0.93). These results demonstrated that the cyclic voltammetry is a useful tool to remark differences among propolis according their antioxidant profile.