Immobilization of starch-converting enzymes on surface-modified carriers using single and co-immobilized systems: properties and application to starch hydrolysis

Starch-converting enzymes, α-amylase and glucoamylase, were immobilized on surface-modified carriers using a co-immobilized as well as a single system. Hydrophilic silica gel and DEAE-cellulose entrapped in alginate beads were selected as the most effective carriers. The hydrophilic and the hydrophobic characteristics of carriers were made by polyethylimine-coating and silanization, respectively, and confirmed by contact angle measurements. All co-enzymes immobilized on hydrophilic carriers exhibited the highest activities in each modulation. The lower Km values (0.102 mg/ml for hydrophilic silica gel and 0.099 mg/ml for DEAE-cellulose entrapped in beads) than that of native enzyme (0.199 mg/ml) represented the higher affinity of immobilized enzymes to substrates. When performing the hydrolysis of starch, the shifts of optimum temperature from 50 to 60 °C (or activation energy) and pH from 5.0 to 5.5 after immobilization were due to covalent bond formation and polyionic characteristics of carriers, respectively. The co-enzymes immobilized on hydrophilic silica gel and DEAE-cellulose entrapped in alginate beads exhibited 92.3 and 88.9% of the remaining activity even after 10 times of reuse.