Inactivation of mushroom polyphenoloxidase in model systems exposed to high-pressure carbon dioxide

An aqueous solution containing mushroom polyphenoxidase was exposed at 20, 35 and 45 degrees C for up to 15 min to CO2 at increasing pressure up to 18 MPa. Samples were analysed for residual enzymatic activity and SDS-PAGE patterns. At 20 and 35 degrees C, HP-CO2 allowed non-thermal and irreversible inactivation of polyphenoloxidase with decimal reduction time (D-P) that decreased when pressure increased. At 45 degrees C, complete inactivation was achieved in less than 0.2 min at all CO2 pressures. The pressure sensitivity parameter (Z(P)) of inactivation rate resulted similar at 20 and 35 degrees C (5.4 and 5.5 MPa, respectively). Accordingly, temperature increase from 20 to 35 degrees C caused minor modifications of activation volume (not equal V-Delta) (circa - 1000 cm(3) mol(-1)) but almost doubled the pre-exponential factor of the Eyring equation. SDS-PAGE data showed that polyphenoloxidase inactivation followed mechanisms other than those associated with thermal inactivation and proceeded with no structural changes, probably implying the formation of bindings between molecular CO2 and enzyme terminal groups.