Antioxidant and xanthine oxidase inhibitory activity of Eucommia ulmoides Oliver leaf extracts.

The total phenolic content, flavonoid content, in vitro xanthine oxidase (XOD) inhibitory activity and antioxidant activity (AA) of Eucommia ulmoides Oliver leaf extracts were investigated. The AA investigations included 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, β-carotene/linoleic acid bleaching assay and oxygen radical absorbance capacity (ORAC) test. The ethyl acetate fraction (EE) showed the highest AA and xanthine oxidase inhibitory activity. Whilst the lowest 50% inhibition (IC50) value of this fraction for DPPH free radical scavenging was 0.045mg/mL, its highest ORAC value was 10.57 μmol TE/mg. The highest inhibition rate against linoleic acid oxidation observed was 69.41%, and the lowest IC50 value for xanthine oxidase activity inhibition was 2.47mg/mL. These results show that E. ulmoides leaf extract is a promising source of natural antioxidants because it contains high contents of bioactive compounds, including chlorogenic acid, rutin, hyperin and astragalin, as detected by high-performance liquid chromatography coupled to HPLC-DAD-ESI-MS.