THERMOSTABILITY OF SOLUBLE AND IMMOBILIZED ALPHA-AMYLASE FROM BACILLUS-LICHENIFORMIS

In view of a possible application of the alpha-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-degrees-C. The D-values (95-degrees-C) for inactivation of alpha-amylase, dissolved in tris-HCl buffer, ranged from 6 to 157 min, depending on pH, ionic strength, and Ca2+ and enzyme concentration. The z-value fluctuated between 6.2 and 7.6-degrees-C. On immobilization of the alpha-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-degrees-C) ranged between 17 and 620 min, depending largely on certain environmental conditions. The z-value fluctuated between 8.1 and 12.9-degrees-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.