GLASSY STATE IN RELATION TO THE THERMAL INACTIVATION OF THE ENZYME INVERTASE IN AMORPHOUS DRIED MATRICES OF TREHALOSE, MALTODEXTRIN AND PVP

The stabilization of invertase by its incorporation in aqueous trehalo se and polymer solutions, followed by freeze-drying and desiccation to 'zero' moisture content was studied. The dried amorphous preparations of trehalose, maltodextrin (MD; DE = 10.9), and poly(vinyl)pyrrolidon e (PVP), molecular weights 360000, 40000 and 10000, greatly protected invertase-as compared with its behavior in liquid solution-from heat i nactivation at elevated temperatures. Significant invertase inactivati on was observed in heated PVP and MD matrices kept well below their gl ass-transition temperature. Under glassy conditions the extent of enzy me protection by MD and PVP systems was related to their glass-transit ion temperature (T-g) since systems of higher T-g afforded better prot ection. However the data for trehalose deviated from this behavior sin ce invertase stabilization was higher than expected on the basis of th e results obtained with polymer matrices. Present results suggest that invertase inactivation in dried amorphous systems cannot be adequatel y explained by the glass-transition theory and this is particularly tr ue for trehalose, for which some additional mechanism of enzyme protec tion is likely to operate. Copyright (C) 1996 Elsevier Science Limited