Pectin hydrolysis in cashew apple juice by Aspergillus aculeatus URM4953 polygalacturonase covalently-immobilized on calcium alginate beads: A kinetic and thermodynamic study

摘要

The kinetics and thermodynamics of pectin hydrolysis in cashew apple juice by polygalacturonase (PG) from Aspergillus aculeatus URM4953 covalently-immobilized on calcium alginate beads were investigated. Immobilized PG activity in cashew apple juice was the highest at 20 degrees C, showing a maximum hydrolysis rate of 58.2 mg/mL.min, a catalytic constant of 166.2 s(-1) and an affinity constant of 113.0 mg/mL Since the enzyme exhibited an allosteric behavior, the hydrolysis rate was modeled, with excellent accuracy, by the Hill Equation as function of pectin concentration. The Hill coefficient increased from 3 to 5 with increasing temperature from 20 to 50 degrees C, evidencing a positive cooperativity mechanism. The reaction activation energy and the standard enthalpy variation of enzyme unfolding were 80.3 and 16.6 kJ/mol, respectively. Consistently with the kinetic results, PG-catalyzed pectin hydrolysis proceeded with maximum spontaneity at 20 degrees C, showing activation Gibbs free energy, enthalpy and entropy of 59.3 kJ/mol, 77.9 kJ/mol and 63.4 J/mol.K respectively. Immobilized PG was successful in the hydrolysis of cashew apple juice pectin, requiring a low temperature to act optimally. (C) 2018 Elsevier B.V. All rights reserved.