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

Abstract

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\u202f°C, showing a maximum hydrolysis rate of 58.2\u202fmg/mL·min, a catalytic constant of 166.2\u202fs-1 and an affinity constant of 113.0\u202fmg/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\u202f°C, evidencing a positive cooperativity mechanism. The reaction activation energy and the standard enthalpy variation of enzyme unfolding were 80.3 and 16.6\u202fkJ/mol, respectively. Consistently with the kinetic results, PG-catalyzed pectin hydrolysis proceeded with maximum spontaneity at 20\u202f°C, showing activation Gibbs free energy, enthalpy and entropy of 59.3\u202fkJ/mol, 77.9\u202fkJ/mol and 63.4\u202fJ/mol·K, respectively. Immobilized PG was successful in the hydrolysis of cashew apple juice pectin, requiring a low temperature to act optimally.