Thermal and combined pressure-temperature inactivation of orange pectinesterase: Influence of pH and additives

Inactivation of commercially available orange pectinesterase (PE) was inves tigated under isothermal and isothermal-isobaric conditions. In both cases, inactivation data could be accurately described by a fractional conversion model. The influence of enzyme concentration, pH, Ca2+ concentration, and sucrose on the inactivation kinetics was studied. Enzyme stability against heat and pressure increased by increasing enzyme concentration. An increase d Ca2+ concentration caused sensitization to temperature and increased the residual fraction active PE after thermal treatment. To the contrary, in th e case of pressure treatment, decreasing Ca2+ concentrations increased pres sure inactivation. The remaining fraction active PE after pressure treatmen t was not influenced by the addition of Ca2+ ions. Acidification accelerate d thermal as well as pressure-temperature inactivation, whereas in the pres ence of sucrose an increased temperature and pressure stability of orange P E was observed. Sucrose had no influence on the remaining activity after th ermal treatment, but it increased the residual fraction after pressure trea tment. The remaining fraction was for all additives studied independent of the pressure and temperature level applied except for the inactivation in a n acid medium, when a decrease of the residual fraction was observed with i ncreasing temperature and pressure.