THERMAL-STABILITY OF DEHYDRATED ALPHA-AMYLASE IN TREHALOSE MATRICES IN RELATION TO ITS PHASE-TRANSITIONS

Thermal stability of alpha-amylase in trehalose matrices of reduced mo isture 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 alpha-amylase but when trehalose was present an extraordinary stabilization was ach ieved. Even in an initially rubbery condition, the protective effect o f trehalose could be assessed up to 100 degrees C. Deactivation kineti cs in the range 80-100 degrees C were related to crystallization of am orphous trehalose which would occur because the system was above the g lass transition temperature According to available water, at most 50% of amorphous trehalose would crystallize. The remaining amorphous treh alose phase would increase its glass transition temperature lending to enhanced enzyme stability. Ar temperatures close to 90 degrees C, tre halose dihydrate crystals start melting, releasing water which could p romote further trehalose crystallization and enzyme deactivation Once trehalose crystallizes, the protective effect may be lost since crysta lline trehalose forms a separated phase no longer associated with the enzyme. These phase transitions were reflected as breaks in the Arrhen ius plots.