The influence of moisture content on the thermostability of Aspergillus oryzae α-amylase

The thermal stability of Aspergillus oryzae α-amylase in systems of different moisture content was investigated. To obtain systems of reduced moisture content the enzyme was freeze-dried with addition of maltodextrin and equilibrated above saturated salt solutions. Other systems applied were aqueous solutions of maltodextrin. The thermal inactivation kinetics could be accurately described by a first-order model in all systems studied except the system at moisture content 0.029 g H2O/g dry basis, which showed a biphasic inactivation pattern. Reduced moisture content had a significant effect on α-amylase thermostability, the enzyme being far more thermostable in maltodextrin systems at reduced moisture content than in aqueous solutions. When the moisture content decreased from 3.5 g H2O/g dry basis to 0.029 g H2O/g dry basis, the temperature range of inactivation increased from 70–75 °C to 100–115 °C. The activation energy (z-value) of thermal inactivation was also affected by the moisture content in the system.