Inactivation and reactivation of horseradish peroxidase treated with supercritical carbon dioxide

Effects of supercritical carbon dioxide (SCCO2) on the activity of horseradish peroxidase (HRP) in pH 5.6 acetate buffer solution were investigated. SCCO2 treatment could effectively inactivate HRP. Higher pressure, higher temperature, and longer treatment time caused more inactivation. The maximum reduction of HRP activity reached nearly 90% at 30 MPa and 55 degrees C for 60 min. Analysis of first-order reaction kinetic data (characterized by a rate constant k and by a decimal reduction time D) showed that D value was closely related to the pressure and temperature of SCCO2 treatment. Higher pressures or higher temperatures resulted in lower D values (higher k), the D value of HRP was minimized to 64.52 min treated by the combination of 30 MPa and 55 degrees C. The Z (p), representing the range of applied pressure between which the D values change by a factor of 10, was 114.81 MPa. The activity of HRP treated by SCCO2 was reactivated significantly after initial 7-day storage at 4 degrees C apart from the samples at 30 MPa for 60 min, indicating the HRP inactivation may be reversible and the reactivation of HRP is dependent on the pressure level and treatment time.