Characterization of antioxidants present in bitter tea (Ligustrum pedunculare)

The present study examined the antioxidants present in bitter tea (Ligustrum pedunculare). It was found that the crude glycoside fraction strongly protected human low-density lipoprotein (LDL) from oxidation. Further column chromatography led to purification of eight phenylethanoid or monoterpene glycosides: lipecloside A-I, lipecloside A-II, lipecloside B-I, lipecloside B-III, lipecloside B-V, lipecloside B-VI, osmanthuside B, and anatolioside. It was found that lipecloside A-I, lipecloside A-II, lipecloside B-V, and lipecloside B-VI were protective, whereas the other four compounds did not protect human LDL from Cu2+-medicated oxidation. Lipecloside A-I, lipecloside A-II, lipecloside B-V, and lipecloside B-VI also had a scavenging effect on 2,2-diphenyl-1-picrylhydrazyl free radical (DIPPH), comparable to that of alpha-tocopherol. The inhibitory effect of these four phenylethanoid or monoterpene glycosides on oxidation of human LDL and alpha-tocopherol was dose-dependent at concentrations of 5-40 muM. The present results demonstrate that bitter tea as a beverage contains effective antioxidants that may have benefits similar to those of green tea in terms of antioxidant activity.