Abstract: Duck pear (Pyrus bretschneideri Rehder) tends to develop browning core after 55 to 60 days storage at low temperature (0℃). Following physiological changes of the duck pear during storage at different temperature were investigated: (1) As compared with 20℃, ethylene release is obviously decreased and its peak is retarded for 15 days at 0℃. Levels of internal ethylene are variant at different individuals harvested at same time. Concentrations of internal ethylene are in accord with ethylene release. The higher internal ethylene is, the easier the pear core becomes brown. (2) At 0℃, activity of polyphenol oxidase in the core increases with ethylene release enhancement. After ethylene peak passes, its activity is lower than before. (3) The electric conductivity of cores is higher at 0℃ than at 20℃. During post climacteric period, the electric conductivity increases irreversibly, then browning core occurs. From above results, it is concluded that interactions between two factors induce the browrang core of the duck pears at low temperature. One is chilling injury caused by low temperature, another is ethylene function. They stimulate the activity of polyphenol oxidase and enhance the membrane permeability.

Key words: Duck pears, Ethylene, Ratio of electric conductivities, Polyphenol oxidase, The browning cores of duck pears