Free-radical scavenging capacity and antioxidant activity of selected plant species from the Canadian prairies

Ethanolic extracts from the roots of wild licorice (Glycyrrhiza lepidota), narrow-leaved echinacea (Echinacea angustifolia), senega (Polygala senega), leaves of bearberry (Arctostaphylos uva-ursi) and aerial parts of two varieties of horsetail (Equisetum spp.) were prepared and evaluated for their free-radical scavenging capacity and their antioxidant activity, by a number of chemical assays. Assays employed included a β-carotene-linoleic acid (linoleate) model system, reducing power, scavenging effect on the DPPH free radical and capacity to scavenge hydroxyl free radicals (HO), by use of electron paramagnetic resonance (EPR) spectroscopy. The bearberry-leaf extract consistently exhibited the highest antioxidant activity based on the tests performed, and seems to be a promising source of natural antioxidants. The polyphenolic constituents appear to be responsible, at least in part, for the extractʹs radical-scavenging capacity. Research is progressing to characterize the antioxidant compounds in the bearberry-leaf extract and their mode of action in imparting antioxidant activity to various food systems.