Thermal Stability of Dehydrated α-Amylase in Trehalose Matrices in Relation to its Phase Transitions

Abstract

Thermal stability of α-amylase in trehalose matrices of reduced moisture content was studied as affected by phase transitions occurring as a result of increasing temperature at a moisture content of 50 g/kg. Removal of water greatly enhanced thermal stability of α-amylase but when trehalose was present an extraordinary stabilization was achieved. Even in an initially rubbery condition, the protective effect of trehalose could be assessed up to 100 °C. Deactivation kinetics in the range 80–100 °C were related to crystallization of amorphous trehalose which would occur because the system was above the glass transition temperature. According to available water, at most 50% of amorphous trehalose would crystallize. The remaining amorphous trehalose phase would increase its glass transition temperature leading to enhanced enzyme stability. At temperatures close to 90 °C, trehalose dihydrate crystals start melting, releasing water which could promote further trehalose crystallization and enzyme deactivation. Once trehalose crystallizes, the protective effect may be lost since crystalline trehalose forms a separated phase no longer associated with the enzyme. These phase transitions were reflected as breaks in the Arrhenius plots.