KINETICS FOR HEAT AND PRESSURE-TEMPERATURE INACTIVATION OF BACILLUS-SUBTILIS ALPHA-AMYLASE

The kinetic parameters for thermal inactivation of Bacillus subtilis a lpha-amylase (15 mg/ml in Tris HCl buffer at pH 8.6) were determined f rom isothermal experiments using a two step linear regression method. At ambient pressure, the inactivation of Bacillus subtilis alpha-amyla se could be described by a first order kinetic model. The activation e nergy (E(a)) was 266 kJ/mole and the rate constant (k(ref)) at referen ce temperature (50 degrees C) 6.310(-5) min(-1). Subsequently the ina ctivation due to combined pressure and temperature was investigated in a pressure range of 0 to 550 MPa and a temperature range of 40 to 80 degrees C. The kinetic parameters for pressure-temperature inactivatio n of BSA were estimated applying a non-linear regression method on a f irst order kinetic model. E(a)-values were found to decrease and k(ref )-values to increase with increasing pressure. Furthermore, the influe nce of glycerol on the thermal and pressure-temperature stability of B acillus subtilis alpha-amylase was investigated. In both cases, glycer ol seemed to enhance the stability since it caused a decrease of the k (ref) values at any pressure. At ambient pressure, the kinetic paramet ers for thermal inactivation in the presence of glycerol were an E(a)- value of 265 kJ/mole and a k(ref)-value of 4.110(-6) min(-1). Adding glycerol lowered the k(ref)-value, but had no significant influence on the activation energy. Finally, the activation volume for pressure-te mperature inactivation of BSA was calculated. At reference temperature the activation volume was -39.7 cm(3)/mole and it decreased linearly with increasing temperature. In the presence of glycerol, the activati on volume at reference temperature was -55.1 cm(3)/mole.