Hydrolysis of starch particles using immobilized barley α-amylase

Abstract

Barley α-amylase has been immobilized on silica particles with diameters between 0.5 and 10 μm using a covalent binding method. Immobilization procedures were adjusted to optimize enzyme activity. The effects of product inhibition, thermal stability and operational stability have been determined. The feasibility of using the immobilized enzyme to hydrolyze wheat starch particles at temperatures below the gelatinization temperature (<55 °C) was proven. The optimal conditions for the hydrolysis were found to be: pH 4.5, 40 °C, calcium ion concentration 0.002 M and immobilized enzyme loading of 30 mg/ml. At these conditions, the immobilized enzyme was able to hydrolyze wheat starch particles at concentrations as high as 100 mg/ml with a final conversion of 90% after 24 h of operation. Maltose and glucose were found to inhibit the immobilized enzyme in a similar manner as reported previously using soluble enzyme. Although the thermostability of the immobilized enzyme was superior to the soluble enzyme, the immobilized enzyme degraded at the same rate as the soluble enzyme during cold wheat starch hydrolysis (operational stability unchanged). Model equations are presented for product inhibition, hydrolysis kinetics and enzyme degradation. Using best-fit parameters, the equations are shown to fit the experimental data well.