Combined effects of trehalose and cations on the thermal resistance of β-galactosidase in freeze-dried systems

Abstract

The purpose of this study was to investigate the combined effects of trehalose and cations on the preservation of β-galactosidase in freeze-dried systems and their relationship to physical properties. Differential scanning calorimetry was employed to measure the glass transition temperature ( T g) and the endothermal peak area, related to the amount of crystalline trehalose dihydrate present in the samples. In systems in which the trehalose matrix was humidified to conditions which allowed a high proportion of trehalose to crystallize, the enzyme was rapidly inactivated upon heating at 70°C. In these conditions the addition of CsCl, NaCl and particularly KCl or MgCl 2, improved the enzyme stability with respect to that observed in matrices containing only trehalose. For a given moisture content, addition of salts produced very little change on the glass transition temperature; therefore the protective effect could not be attributed to a higher T g value. The crystallization of trehalose dihydrate in the humidified samples was delayed in the trehalose/salt systems (principally in the presence of Mg 2+) and a parallel improvement of enzyme stability was observed.