Degradação de pectina em suco de caju por poligalacturonase de Aspergillus aculeatus URM4953 imobilizada covalentemente em pérolas de alginato

Abstract

Polygalacturonase (PG) is the main pectinolytic enzyme that catalyzes the degradation reaction of pectin. Its immobilized form is generally preferred because of the possibility of numerous reuses. Based on this, the present work aimed to immobilize and perform kinetic and thermodynamic biochemical characterization of polygalacturonase (PG) from Aspergillus aculeatus URM4953 to process cashew juice. The immobilization optimization process had a maximum redemption of 95%. The optimum pH of both forms of PG (free and immobilized) presented two evident peaks at pH 4.0 (acid) and pH 7.0 (neutral). Although the PG optimum temperature differed in both forms, free (50 ° C) and immobilized (40 ° C), PGs exhibited similar residual activity over different temperatures. The affinity of the different forms of PG decreased with increasing temperature, being higher for the enzyme immobilized. However, from the kinetic point of view the free PG presented better general behavior (higher Vmax and Kcat). The thermodynamic parameters of thermoinactivation of immobilized PG such as enthalpy, entropy and free energy of gibbs, suggested a predominant mechanism of reversible denaturation, which allowed 4 successive reuses of PG immobilized with only 34% loss of activity. For the processing of cashew juice using only immobilized PG, the temperature of the highest degradation of the pectic content was at 20 °C and its kinetics was modeled by the Hill equation (due to the presented allosteric behavior). Hill's number increased from 3 (20 °C) to 5 (50 °C), indicating a positive cooperation mechanism. The activation energy (E*) and the standard entropy of equilibrium unfolding of the reaction were 80.31 and 16.57 kJ / mol, respectively. Both kinetic and thermodynamic parameters of hydrolysis corroborated and demonstrated the higher hydrolysis expontance of pectin of cashew juice at 20 ° C, exhibiting values of and of 59.3 kJ/mol, 77.9 kJ/mol and 63.4 J/K.mol, respectively. These results showed a satisfactory performance of PG, mainly in its immobilized form, and it can be laterally used for the theoretical basis of applications of this enzyme in different industrial processes.