Actinidin is the sulfhydryl protease of kiwi fruit. It can have applications in the food industry replacing other plant sulfhydryl proteases like papain and ficin, as milk clotting enzyme for traditional and novel dairy products, as meat tenderizer and beer clarifier. High hydrostatic pressure (HHP) will allow the controlled inactivation of actinidin after it has been applied and caused the desirable extent of clotting or tenderization, respectively. Thermal inactivation and inactivation by HHP (200-800 MPa) combined with moderate temperature (25-50 degrees C) of the endogenous actinidin in kiwi fruit juice was studied. The enzyme activity was measured spectrophotometrically based on the hydrolysis of a chromophore-peptide compound. Actinidin inactivation followed first order kinetics at the studied processing conditions. The activation energy E, and the activation volume V(a) were expressed as a function of pressure and temperature, respectively. The enzyme inactivation was modeled by a single multi-parameter equation in the studied temperature and pressure domain. The developed kinetics allow the selection of optimal HHP process conditions for achieving the desirable enzyme activity control after the targeted proteolysis has been achieved in products where the kiwi fruit actinidin has been applied. (C) 2009 Elsevier Ltd. All rights reserved.