Inactivation of orange pectinesterase by combined high-pressure and -temperature treatments: A kinetic study

Pressure and/or temperature inactivation of orange pectinesterase (PE) was investigated. Thermal inactivation showed a biphasic behavior, indicating t he presence of labile and stable fractions of the enzyme. in a first part, the inactivation of the labile fraction was studied in detail. The combined pressure-temperature inactivation of the labile fraction was studied in th e pressure range 0.1-900 MPa combined with temperatures from 15 to 65 degre es C. Inactivation in the pressure-temperature domain specified could be ac curately described by a first-order fractional conversion model, estimating the inactivation rate constant of the labile fraction and the remaining ac tivity of the stable fraction. Pressure and temperature dependence of the i nactivation rate constants of the labile fraction was quantified using the Eyring and Arrhenius relations, respectively. By replacing in the latter eq uation the pressure-dependent parameters (E-a, k(refT)) by mathematical exp ressions, a global model was formulated. This mathematical model could accu rately predict the inactivation rate constant of the labile fraction of ora nge PE as a function of pressure and temperature. In a second part, the sta ble fraction was studied in more detail. The stable fraction inactivated at temperatures exceeding 75 degrees C. Acidification (pH 3.7) enhanced therm al inactivation of the stable fraction, whereas addition of Ca2+ ions (1 M) suppressed inactivation. At elevated pressure (up to 900 MPa), an antagoni stic effect of pressure and temperature on the inactivation of the stable f raction was observed. The antagonistic effect was more pronounced in the pr esence of a 1 M CaCl2 solution as compared to the inactivation in mater, wh ereas it was less pronounced for the inactivation in acid medium.