Covalent immobilization of alpha-amylase onto pHEMA microspheres: preparation and application to fixed bed reactor

Microspheres of poly(2-hydroxyethyl methacrylate) with and without cross-linker were prepared by suspension polymerization. As the amount of cross-linker increased, the equilibrium water content, enzyme loading, immobilization efficiency and recovered activity were all adversely affected. Enzyme alpha-amylase was immobilized onto the microspheres after activation with epichlorohydrin. The Km value for the immobilized enzyme (0.90% w/v) was much greater than that of the free enzyme (0.53% w/v). It was found that the inactivation constant (ki) increased from 2.23 x 10(-8) min-1 at 20 degrees C to 1.45 x 10(-4) min-1 at 60 degrees C. Since the enzyme activity increased as the temperature increased, the temperature profile yielded a peak at 50 degrees C. For free enzyme this is at 45 degrees C. The residence time was proportional to the percentage hydrolysis until a residence time of 12 min was reached. Beyond this the activity increase could not match the increase in residence time. The pH profile yielded a broadening upon immobilization in addition to a small shift to higher pH (from 5.5 to 6.0). The continuous run at 30 degrees C, 1.0% w/v starch concentration and flow rate of 40 cm3 h-1 led to only 20% loss in activity after a 120 h operation.