>Kinetics for heat and pressure‐temperature inactivation of bacillus subtilis α‐amylase

Abstract

The kinetic parameters for thermal inactivation of Bacillus subtilis α‐amylase (15 mg/ml in Tris HCI buffer at pH 8.6) were determined from isothermal experiments using a two step linear regression method. At ambient pressure, the inactivation of Bacillus subtilis α‐amylase could be described by a first order kinetic model. The activation energy (E_a) was 266 kJ/mole and the rate constant (k_ref) at reference temperature (50°C) 6.3∗10⁻⁵ min⁻¹. Subsequently the inactivation 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°C. The kinetic parameters for pressure‐temperature inactivation of BSA were estimated applying a non‐linear regression method on a first order kinetic model. E_a‐values were found to decrease and k_ref‐values to increase with increasing pressure. Furthermore, the influence of glycerol on the thermal and pressure‐temperature stability of Bacillus subtilis α‐amylase was investigated. In both cases, glycerol seemed to enhance the stability since it caused a decrease of the k_ref values at any pressure. At ambient pressure, the kinetic parameters for thermal inactivation in the presence of glycerol were an E_a‐value of 265 kJ/mole and a k_ref‐value of 4.1 ∗10⁻⁶ min⁻¹. Adding glycerol lowered the k_ref‐value, but had no significant influence on the activation energy. Finally, the activation volume for pressure‐temperature inactivation of BSA was calculated. At reference temperature the activation volume was ‐39.7 cm³/mole and it decreased linearly with increasing temperature. In the presence of glycerol, the activation volume at reference temperature was ‐55.1 cm³/mole.