Immobilization of polygalacturonase from Aspergilus niger onto glutaraldehyde activated Nylon-6 and its application in apple juice clarification

The application of immobilized enzyme for catalyzing various biotransformation processes is a widely used approach at present. This work mainly focused on the immobilization of polygalacturonase from Aspergillus niger Van Tieghem (MTCC 3323) on Nylon-6 by covalent binding, keeping in view its applicability in apple juice clarification. The immobilized enzyme was characterized in terms of kinetic parameters, thermal stability and reusability. The enzyme was immobilized onto glutaraldehyde-activated Nylon-6 by covalent binding and the efficiency of immobilization was found to be 40%. The immobilization yielded a protein loading of 70 μg g−1 of Nylon-6. Immobilized enzyme showed maximum activity at a temperature of 50 °C and pH 5.0. The enzyme was stable between pH 4.0–5.5. The immobilized enzyme could be reused through 4 cycles with almost 50% retention of its original activity. It had increased thermostability over its soluble form at 25 °C and 45 °C. Kinetic parameters Km and Vmax were found to be 7.6 mg ml−1 and 41.66 μmol of galacturonic acid/ml/min, respectively. The immobilized enzyme when used for apple juice clarification showed about 50% increase in transmittance of apple juice at 650 nm. This increase was observed at enzyme concentration of 20 U ml−1 apple juice, temperature 50 °C and incubation time of one hour. The optimization of these factors, which affect the stability and productivity of the immobilized system, resulted in an increase in enzyme stability and the possibility of economic application of immobilized enzyme at large scale apple juice clarification