Thermodynamic and kinetic studies on pectinase extracted from Aspergillus aculeatus: Free and immobilized enzyme entrapped in alginate beads

The kinetics and thermodynamics of Aspergillus aculeatus pectinase, either free or immobilized in alginate beads, were investigated. Pectinase immobilization ensured an enzyme immobilization yield of 59.71%. The irreversible denaturation of pectinase in both preparations was evaluated at temperatures ranging from 30 to 60 °C. When temperature was raised, the first-order thermal denaturation constant increased from 0.0011 to 0.0231 min−1for the free enzyme and from 0.0017 to 0.0700 min−1for the immobilized one, respectively. The results of residual activity tests enabled us to estimate, for denaturation of both free and immobilized pectinase, the activation energy (E⁎d= 85.1 and 101.6 kJ·mol−1), enthalpy (82.59 ≤ ΔH⁎d≤ 82.34 kJ·mol−1and 99.11 ≤ ΔH⁎d≤ 98.86 kJ·mol−1), entropy (−63.26 ≤ ΔS⁎d≤ −63.85 J·mol−1·K−1and −5.50 ≤ ΔS⁎d≤ −5.23 J·mol−1·K−1) and Gibbs free energy (101.8 ≤ ΔG⁎d≤ 104.7 kJ·mol−1and 100.6 ≤ ΔG⁎d≤ 102.0 kJ·mol−1). The integral activity of a continuous system using the free and immobilized enzyme was also predicted, whose results indicated a satisfactory enzyme long-term thermostability in both preparations at temperatures commonly used to clarify juice. These results suggest that both free and immobilized pectinase from A. aculeatus may be profitably exploited in future food industrial applications, with special concern to the immobilized enzyme because of its reusability.