title: Thermostability of soluble and immobilized alpha-amylase from Bacillus licheniformis.
abstract: 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 Ca(2+) 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.
authors.affiliation: Laboratory of Food Technology, Faculty of Agricultural Science, Katholieke Universiteit Leuven, Belgium.
authors.forename: S
authors.initials: S
authors.lastname: De Cordt
authors.forename: K
authors.initials: K
authors.lastname: Vanhoof
authors.forename: J
authors.initials: J
authors.lastname: Hu
authors.forename: G
authors.initials: G
authors.lastname: Maesmans
authors.forename: M
authors.initials: M
authors.lastname: Hendrickx
authors.forename: P
authors.initials: P
authors.lastname: Tobback