Purification and Antioxidant Activity of Polyphenols from Apple Tree Leaves

The preliminary purification of a polyphenols-rich extract from apple tree leaves prepared in our laboratory was carried out using macroporous resin adsorption,followed by further purification and HPLC analysis. Along with this,the preliminarily purified extract was tested for its ability to scavenge DPPH free radicals and nitrite. X-5 resin was the best resin found for adsorbing and desorbing apple tree leaf polyphenols among eight types of resins tested. The optimum adsorption/ desorption conditions of X-5 resin were determined to be:sample concentration,3.658 mg/mL; sample pH,3; sample flow rate,2.0 mL/min; ethanol concentration for desorption,40%; desoprtion flow rate,1.0 mL/min; and desorption solvent volume,4 BV. After the purification under the above conditions,the purity of polyphenols was increased from 10.07% to 38.55%. The adsorption of X-5 resin towards apple tree leaf polyphenols was an exothermic course and accorded with the Langmuir isothermal model and the Freundlich isothermal model. The purified extract presented stronger DPPH free radical and nitrite scavenging capacities than the native extract. The HPLC analysis showed that the content of phlorizin was 2.45% in apple tree leaves and 47.61% in the further purified extract,which accounted for 91.51% of the total polyphenols.