Chemical compositions and antioxidant activities of water extracts of Chinese propolis.

The present study investigated the chemical composition and antioxidant activity of the water extract of propolis (WEP) collected from 26 locations in China. Spectrophotometry was used to determine the physicochemical properties and the chemical constituents of WEP. Phenolic compounds in WEP were identified by RP-HPLC-DAD with reference standards. The antioxidant activities [characterized by reducing power and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging ability] of WEP were also measured. Results show that epicatechin, p-coumaric acid, morin, 3,4-dimethoxycinnamic acid, naringenin, ferulic acid, cinnamic acid, pinocembrin, and chrysin are the major functional phenolic compounds in Chinese WEPs. Furthermore, most WEPs show strong antioxidant activities, which are significantly correlated with E(1cm)(1%), an index for the estimation of the quality of WEP. WEPs also contain many more active constituents than ethanol extracts of propolis.