Thermostability of soluble and immobilized α‐amylase from Bacillus licheniformis

In view of a possible application of the α‐amylase from Bacillus licheniformis as a time–temperature integrator for evaluation of heat processes, 11 thermal inactivation kinetics of the dissolved and covalently immobilized enzyme were studied in the temperature range 90–108°C. The D ‐values (95°C) for inactivation of α‐amylase, dissolved in tris‐HCl buffer, ranged from 6 to 157 min, depending on pH, ionic strength, and Ca 2+ and enzyme concentration. The z ‐value fluctuated between 6.2 and 7.6°C. On immobilization of the α‐amylase by covalent coupling with glutaraldehyde to porous glass beads, the thermoinactivation kinetics became biphasic under certain circumstances. For immobilized enzyme, the D ‐values (95°C) ranged between 17 and 620 min, depending largely on certain environmental conditions. The z ‐value fluctuated between 8.1 and 12.9°C. In each case of biphasic inactivation, the z ‐value of the stable fraction (with the higher D ‐values) was lower than the z ‐value of the labile fraction. © 1992 John Wiley & Sons, Inc.