Immobilization of glucoamylase on polypropylene fibers modified by radiation induced graft copolymerization

Glucoamylase (GA) had been covalently immobilized on polypropylene grafted poly-acrylamide (PP-g-P(AAm)) and polypropylene grafted poly-acrylic acid (PP-g-P(AAc)) fibers by the use of carbodiimide (CDI) as a coupling agent. The polymeric support for enzyme immobilization was prepared using radiation that induced graft copolymerization of acrylamide (AAm) and acrylic acid (AAc) monomers, individually, onto polypropylene fibers followed by chemical treatments. Effects of pH and temperature on the relative activity, as well as storage stability and reusability of the immobilized enzyme, were studied. The kinetic effect of immobilization was also studied to find that, the K-m values for glucoamylase immobilized on PP-g-P(AAc) and PP-g-P(AAm) fibers are 3.4 and 5.88, respectively, i.e., higher than that for free glucoamylase of K-m 1.6. An enhancement in the thermal stability of the glucoamylase is observed upon immobilization. The optimum temperature for the immobilized enzyme on both PP-g-P(AAc) and PP-g-P(AAm) was found to be shifted 5 degrees C higher than that of the free enzyme at 55 degrees C. Investigation of reusability of the immobilized enzyme showed that after 10 cycles the immobilized enzyme retained 60% and 45% of its original activity for PP-g-P(AAc) and PP-g-P(AAm) carriers, respectively.