Preparation of a Calcium Alginate-Coated Polypyrrole/Silver Nanocomposite for Site-Specific Immobilization of Polygalacturonase with High Reusability and Enhanced Stability

Abstract

Polygalacturonase (PG) catalyses the hydrolysis of pectin substances and is commonly used in the textile and food industries. Herein, PG was purified from Arabian balsam using three techniques (ammonium sulfate precipitation, ion exchange chromatography, and gel filtration) with a recovery of 11.2% and tenfold purification. The molecular weight of the purified PG was estimated to be 75.5 kDa using a Sephadex G-150 column. To improve the stability and reusability of the purified enzyme, a novel method to immobilize PG through calcium alginate-coated polypyrrole/silver nanocomposite was described. The immobilized PG was characterized by FTIR, TGA, SEM, EDX, and Raman spectroscopy. The immobilization efficiency was 84.4%. Excellent long-term storage stability of the immobilized PG was demonstrated with 83% of the initial activity preserved after 60 days. The immobilized PG was highly reusable, showing high activity (91% and 68%) after five and ten cycles. The immobilized PG showed improved stability to temperature and pH relative to that of the free enzyme. The Km and Vmax were determined to be 0.368 mg/mL and 5.33 µmol/mL for the immobilized PG and 0.667 mg/mL and 7.38 µmol/mL for free PG, respectively. Improved storage stability, catalytic efficiency (Vmax/Km), and reusability of the immobilized PG make it ideal for biotechnological and industrial applications.