Abstract: The enzyme browning mechanism of pingguo pear (Pyrus ussuriensis Var. Ovoidea) and Duch pear (pyrus bretechneideri Rehd) was studied by determining the PH Value. soluble solid. degree of browning .total phenolics and polyphenol oxidase activity. During storage both PH value and soluble solids were in a general trend of decreasing However the phenolic content and activity of polyphenol oxidase were on the contrary;.It was consistent with the increasing degree of browning The combining capabibity of phenolics and polyphenol oxidase with other materials is in the following order pyrogallic acid>catechol>chlorgenic acid>caffeic acid.Vitamin C and reducing sugar had little effect on browning .

Key words: Pingguo pear (Pyrus ussuriensis Var. Ovoidea ) Enzyme browning Polyphenol oxidase Phenolic compounds