Chemical characterization and antioxidant properties of Canadian propolis

Abstract

Propolis is a multifunctional material collected and used by honey bees in the construction and maintenance of their hives. It has been used in folk medicine for centuries. Concentrations of major constituents and antioxidant characteristics of ethanolic extracts of three samples of propolis (EEPs) collected from different geographical locations in Canada (Saskatchewan, Ontario and British Columbia) were determined. Twenty-one compounds were identified in each EEP, of which 18 were polyphenols. Semi-quantitative measurements showed that benzyl caffeate, pinocembrin, sakuranetin and pinobanksin-3-acetate were most abundant in propolis from Ontario. Total phenolic content of EEPs were quantified by using the Folin–Ciocalteu reagent which ranged between 410.81 and 429.61 mg GAE/g EEP. Free radical scavenging activities of propolis were confirmed by use of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and by using Nrf2 Luciferase reporter cell lines. The three EEPs exhibited strong scavenging of free radicals, and protective activity against oxidative stress caused by exposure to H₂O₂ in this in vitro system. These results support the use of propolis from these regions of Canada as a source of natural antioxidants.