Kinetic properties and thermal behaviour of polygalacturonase used in fruit juice clarification

Kinetic properties and thermal inactivation of polygalacturonase (PG) assayed in commercial preparations (Rapidase C80, Pectinase CCM and Pectinex 3XL) were studied. The PG activities in all samples followed Michaelis–Menten kinetics and their catalytic efficiencies were calculated. The optimum pH for enzyme activity was 4.7 for Pectinex 3XL and 4.0 for both Rapidase C80 and Pectinase CCM. The PG optimum temperature lay within the range 50–55 °C. The activation energies of Rapidase C80, Pectinase CCM and Pectinex 3XL PG were 26.5, 45.6 and 4.2 kJ mol−1, respectively. The thermal inactivation curves were not linear in the range 40–60 °C. The biphasic curves fitted to a two-fraction first-order model suggested the presence of two groups of PG isozymes in Rapidase C80 and Pectinase CCM. Half-life values demonstrated that Pectinase PG had the largest thermal stability. Additionally, thermodynamic activation parameters, such as ΔE#, ΔH#, ΔG# and ΔS#, were calculated.