Antioxidant activity and principles of Vietnam bitter tea Ilex kudingcha

The ethyl acetate-soluble fraction of Vietnam bitter tea (Ilex kudingcha) was found to display remarkable free radical-scavenging activities against DPPH (IC50 16.3 μg/ml), OH (IC50 87.5 and 27.3 μg/ml for non-site-specific and site-specific assays, respectively), and O2− (IC50 1.3 μg/ml). This fraction also showed strong suppressive effect on rat liver mitochondrial peroxidation (IC50 7.1 μg/ml) and significantly protected against the oxidation of LDL mediated by either Cu2+ or AAPH free radical (IC50 1.4 and 4.8 μg/ml, respectively). Phytochemical study on this fraction using HPLC showed that kudingcha contained an abundance of phenolic compounds and their structures were deduced on the basis of physicochemical and spectroscopic analyses. The main principles of kudingcha were characterised as thirteen caffeic acid derivatives, including a new compound 3,5-di-O-caffeoyl epi-quinic acid n-butyl ester and three flavonols. The antioxidant activities of isolates were also evaluated.