Improvement of enzymatic properties and decolorization of azo dye: immobilization of horseradish peroxidase on cationic maize starch

The main objective of this work was designed to immobilize the horseradish peroxidase (HRP) into an efficient modified natural polymers carrying positive charges. Thus, cationic maize starch (CMS) was chemically synthesized thru the etherifying agent for native maize starch using sodium hydroxide as a base to deprotonate the hydroxyl groups in the starch and (S)-1-amino-3-chloropropan-2-ol (CHPA) as etherifying reagent. CMS was immobilized with horseradish peroxidase (HRP) to improve its characteristics under a variety of conditions. The findings demonstrated that, at 150 mg CMS, 250 units of HRP, and pH 7.0, the highest immobilization effectiveness of HRP (91%) was achieved. The morphological surface structure depicted via field emission-scanning electron microscope (FE-SEM) and roughness assessments proved that the surface pores and roughness were completely blocked and became rough owing to the adsorption of HRP onto the surface of CMS. The immobilized enzyme was reused 10 times, with 65% of its activity remaining. For immobilized HRP on CMS, the pH optimum of soluble HRP was adjusted from broad (6.0-7.0) to sharp (7.0). The thermal stability of the immobilized enzyme was greater improved while immobilized into CMS. The results illustrated that some of the phenolic compounds were oxidized more efficiently by the immobilized enzyme. Heavy metals and denatured compounds had no impact on the immobilized enzyme. After 1 h of incubation, the immobilized HRP decolorized 97% of the utilized methyl orange (MO) as azo dye model, whereas the soluble form removed 72% of dye. Thus, our findings suggested that the cationized starch immobilized with enzyme could be considered as an alternative effective material for the removal of colored industrial wastewaters.