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

The purpose of this study was to investigate the combined effects of trehal ose and cations on the preservation of beta-galactosidase in freeze-dried s ystems 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 trehal ose dihydrate present in the samples. In systems in which the trehalose mat rix was humidified to conditions which allowed a high proportion of trehalo se to crystallize, the enzyme was rapidly inactivated upon heating at 70 de grees C. In these conditions the addition of CsCl, NaCl and particularly KC l or MgCl2, 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; t herefore the protective effect could not be attributed to a higher T-g valu e. The crystallization of trehalose dihydrate in the humidified samples was delayed in the trehalose/salt systems (principally in the presence of Mg2) and a parallel improvement of enzyme stability was observed. (C) 1999 Els evier Science B.V. All rights reserved.