Antioxidant and xanthine oxidase inhibitory activity of Eucommia ulmoides oliver leaf extracts

ABSTRACT

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, beta-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