5. Reducing power
The antioxidant potential of the extracts was estimated using the method of reduction of potassium ferricyanide. The presence of reducing agents in the extracts induced reduction of the ferric ions (Fe+3) to ferrous ion (Fe+2).
This reduction is measured by the intensity of the blue green color that results.
It absorbs at a wavelength of 700 nm. An increase in absorbance indicates a high reducing power.
The Reducing power obtained for the honey samples are lower than those obtained for the propolis samples (Fig. 6).
On the other hand, the aqueous solution of honey samples gave the best reducing power for the honey samples is water, whereas the methanol extracts of the propolis samples showed a better reducibility.
The diversity of the reducing power of the extracts is probably due to the diversity of phenolic compounds present s in extracts.
The chelating effect of the ions Fe+3 of polyphenols may be related to the highly nucleophilic aromatic rings as specific chelators groups present within the molecule.
The degree of hydroxylation and methylation of the phenolic com-pound and the presence of other non-phenolic compounds such as enzymes (glucose oxidase and catalase) and non-enzyme materials (vitamins and amino acids) may also be involved in this activity.
A highly significant correlation (**P < 0.01, r = 0.59) was observed between the antioxidant activity and polyphenol content (Fig. 7).
This suggests that these compounds (phenolic compounds) appear to contribute very importantly to reducing power of the studied extracts.
Similar results have been reported by several studies, including the work of Blasa et al. (2006) and Beretta et al. (2005).
On the other hand, a significant correlation (*P < 0.05, r = 0.43) was observed between the reducing power and the flavonoid content
This correlation is lower than that obtained by Djeridaneet al. (2007).
Conclusion
In this study, the antioxidants quantification in honey and propolis gave values significantly different between the samples.
These variations are attributed to the floral source, and geographic origin.
Regarding to honey samples, statistical analysis revealed that the aqueous solutions have high level of polyphenol contents. While the best extraction solvent was methanol for flavonoids.
The optimum extraction of total polyphenols and flavonoids of propolis samples was obtained with ethanol.
The comparative study between the antioxidant activity of honey and propolis showed that propolis samples are richer in antioxidants (polyphenols, flavonoids, vitamin C and carotenoids).
Antioxidant activity as measured by the reducing power was found to be higher for propolis samples.
A high correlation was found between the polyphenol content and the reducing power of the analyzed samples. This shows that phenolic compounds are responsible for the antioxidant activity.
Acknowledgments
We want to thank the Algerian Ministry of High Education and Scientific Research for sponsoring this work and my father, Mr. MOUHOUBI Mustapha (a beekeeper) for collecting honey and propolis sample