Antioxidant activity of propolis extracts from Serbia: A polarographic approach

Antioxidant activity (AO) of commercial propolis extracts (PEs), available on Serbian market, was determined by direct current (DC) polarography. Polarographic anodic current of 5.0 mmol L⁻¹ alkaline solution of H₂O₂ was recorded at potentials of mercury dissolution. Decrease of the current was plotted against the volume of gradually added PEs. The volume of PE causing 20% current decrease was determined from the linear part of the plot. Antioxidant activity was expressed in H₂O₂ equivalent (HPEq), representing the volume of PE that corresponds to 1.0 mmol L⁻¹ H₂O₂ decrease. Resulting HPEq ranged between 1.71 ± 0.11 and 8.00 ± 0.18 μL. Range of 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity was from 0.093 ± 0.004% to 0.346 ± 0.006%. Total phenolic content (TCP) of PE with superior AO activity was 5.31 ± 0.05%g GAE, while the extract with the lowest activity contained 1.45 ± 0.02%g GAE. Antioxidant activity, determined by polarographic method, was correlated with DPPH scavenging activity (R² = 0.991) and TCP (R² = 0.985). Validity of obtained results was further confirmed using ANOVA and post hoc Tukey HSD test.