Identification and quantification of antioxidants in Fructus lycii

Fructus lycii was extracted with 95% ethanol and the flavonoid content was determined to be 1.56 mg quercetin-equivalents/g extract. The following antioxidative activities were determined in the extract: (a) radical-scavenging activity (80 μmol trolox equivalent antioxidant capacity/g), measured by its ability to scavenge 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid radical, (b) reducing capacity (301 μmol trolox equivalent reducing capacity/g), measured by its ability to directly donate an electron in the reduction of Fe(III) to Fe(II), and (c) chelating activity (2.5 μmol ethylenediamine-tetraaceticacid equivalents/g), measured by its ability to remove Fe(II) ion from complexation with ferrozine. Three flavonol species in the extract were identified and quantitated by reversed-phase HPLC and their structures confirmed by electrospray ionization-mass spectroscopy: kaempferol (135 μg/g), quercetin (296 μg/g) and myricetin (247 μg/g). These results showed that F. lycii contains substantial amounts of the three antioxidative activities and is rich in flavonoids. The three flavonols accounted for 43% of total flavonoid content.