Electrochemical Detection of Radical Scavenging Polyphenols in Natural Honey: Structure-Activity Relationships

Consumption of antioxidant-rich foods is very likely helpful in protecting human body from deleterious effects of free-radical induced oxidative stress. Polyphenols, the plant secondary metabolites that have been recognized to serve as antioxidants, are among hundreds of minor constituents present in natural honeys. The present work aims to analyze the electrochemical behaviour of polyphenols identified in Malaysian honey samples and elucidate their structure-radical scavenging activity relationships. A total of 18 polyphenols comprises of nine flavonoids, eight phenolic acids, and tannin as identified from our earlier work was studied. Oxidation-reduction (redox) properties of these polyphenols prepared in 0.1 M PBS at pH 7 were analyzed using cyclic voltammetry (CV). The results of the study as shown by cyclic voltammograms indicated that polyphenols with catechol moiety specifically at the B-ring exhibited first anodic (oxidation) peak at low potentials, ranging between +0.173V and +0.404V. Subsequent anodic peaks appeared at much higher potentials were seen for polyphenols bearing a third phenol group (gallic moiety) or other electroactive group (resorcinol moiety). For polyphenols with only isolated phenol group on the B-ring, anodic peak(s) were observed at higher potentials as well. The presence of cathodic (reduction) peaks was observed in several analysed phenolics. It is concluded that the polyphenols varied in their electron donor ability as influenced by their structure as well as hydroxyl group’s number and location, suggesting that they exhibit different radical scavenging activity.