Abstract: The purpose of the present study was to investigate antioxidant constituents in Eucommia ulmoides Oliv. leaves and deeply exploit the resource. Aqueous extract from the leaves of the plant was separated by sequential solvent extraction into chloroform, ethyl acetate extract and n-butanol fractions as well as extraction residue, and the abilities of the extract and these four fractions to scavenge DPPH and hydroxyl free radicals, inhibit linoleic acid peroxidation, chelate ferrous ions and reduce ferric ions were measured and compared with those of BHT and vitamins E and C. Along with this, their total phenol contents were determined. The ethyl acetate and n-butanol fractions had much higher total phenolic content (465.1 mg/g and 286.4 mg/g, respectively) when compared to the aqueous extract and their antioxidant activity in linoleic acid emulsion was higher than that of VE and similar to that of BHT. Moreover, their DPPH free radical scavenging activity was similar to that of VC and remarkably higher than that of BHT. The n-butanol fraction had hydroxyl free radical scavenging activity similar to that of VE. The ethyl acetate fraction had increased ability to reduce ferric ions compared to BHT and VC. All the samples, however, exhibited low ferrous ion-chelating activity. Theses findings collectively indicated that the ethyl acetate extract and n-butanol fractions are rich in antioxidant components and therefore has the potential to be developed as antioxidants.

Key words: Eucommia ulmoides Oliv., antioxidant, free radical, total phenol