Abstract:Using spectrophotometry，Fourier infrared spectroscopy，differential scanning calorimetry，endogenous fluorescence spectroscopy，scanning electron microscopy，and fluorescent molecular probes，the activity，secondary and tertiary structures，and surface microstructure of polyphenol oxidase（PPO）in Lycium ruthenicum Murr.juice under ultra-high pressure（UHP）treatment was studied.Pressures above 400 MPa could reduce polyphenol oxidase activity in Lycium ruthenicum Murr.juice to less than 0.5 U/mL.With increasing pressure，surface hydrophobicity increased，but high pressure had little effect on PPO secondary structure.Changes in thermal denaturation temperature and thermal change enthalpy indicated that pressures above 400 MPa could change the conformation of PPO.Endogenous fluorescence spectroscopy analysis showed that the microenvironment in which tryptophan residues were located increased in polarity，and the tertiary structure of the enzyme changed.High pressure thus changed the apparent morphology of PPO.These studies suggested that the effect of UHP might be to change the spatial structure of PPO，thus changing its enzyme activity.