Inactivation of apple pectin methylesterase induced by dense phase carbon dioxide

The inactivation of apple pectin methylesterase (PME) with dense phase carbon dioxide (DPCD) combined with temperatures (35-55 degrees C) is investigated. DPCD increases the susceptibility of apple PME to the temperatures and the pressures have a noticeable effect on apple PME activity. A labile and stable fraction of apple PME is present and the inactivation kinetics of apple PME by DPCD is adequately described by a two-fraction model. The kinetic rate constants k(L) and k(S) of labile and stable fractions are 0.890 and 0.039 min(-1), and the decimal reduction times D-L and D-S are 2.59 and 58.70 min at 30 MPa and 55 degrees C. Z(T) representing temperature increase needed for a 90% reduction of the D value and the activation energy E-a of the labile fraction at 30 MPa is 22.32 degrees C and 86.88 kJ/mol, its Z(P) representing pressure increase needed for a 90% reduction of the D value and the activation volume V-a at 55 degrees C is 21.75 MPa and -288.38 cm(3/)mol. The residual activity of apple PME after DPCD exhibits no reduction or reactivation for 4 weeks at 4 degrees C.