Reversible immobilization of glucoamylase by ionic adsorption on sepabeads coated with polyethyleneimine

Glucoamylase (GA) from Aspergillus niger was immobilized via ionic adsorption onto DEAE-agarose, Q1A-Sepabeads, and Sepabeads EC-EP3 supports coated with polyethyleneimine (PEI). After optimization of the immobilization conditions (pH, polymer size), it was observed that the adsorption strength was much higher in PEI-Sepabeads than in Q1A-Sepabeads or DEAE-supports, requiring very high ionic strength to remove glucoamylase from the PEI-supports (e.g., 1 M NaCl at pH 5.5). Thermal stability and optimal temperature was marginally improved by this immobilization. Recovered activity depended on the substrate used, maltose or starch, except when very low loading was used. The optimization of the loading allowed the preparation of derivatives with 750 IU/g in the hydrolysis of starch, preserving a high percentage of immobilized activity (around 50%).