Abstract: PPO （Polyphenol Oxidase）-induced enzymatic browning affects the quality of fruits and vegetables.To elucidate the mechanism of cold plasma on PPO and avoid browning，this study investigated the effect of cold plasma on PPO activity and conformation.The results showed that the enzyme activity of PPO could hardly be detected when the treatment time reached 120s and 180s.The active species of cold plasma destroyed the PPO secondary structures with the decrease of α-helix （from 39.92% to 9.47%），and the increase of β-sheet （from 15.32% to 44.30%） （180s）.Fluorescence emission spectrum showed that after cold plasma treatment，the PPO fluorescence intensity decreased from 512.9 to 330.6，and the position of the maximum absorption peak showed a red shift of 1.75nm.The 3D fluorescence spectra showed that the DBD plasma destroyed the polypeptide chain skeleton of the PPO molecule.Atomic force microscopy （AFM） showed that DBD plasma induced PPO molecule aggregation and then depolymerization，thus affecting the enzyme activity.In conclusion，cold plasma treatment changed the secondary and tertiary structures of PPO，and promoted the degeneration of protein oxidation and reduction of enzyme activity，providing theoretical support for the application of cold plasma in the inhibition of enzymatic browning and the maintenance of quality for fruits and vegetables.

Key words: polyphenol oxidase, enzymatic browning, dielectric barrier discharge, cold plasma, enzymatic activity