Thermal stability of invertase in reduced-moisture amorphous matrices in relation to glassy state and trehalose crystallization

The thermal stability of enzyme invertase in reduced-moisture model systems of maltodextrin (MD), polyvynilpyrrolidone (PVP; MW 40,000) and trehalose heated at 90 degrees C was studied. Significant invertase inactivation was observed in heated glassy PVP and MD systems kept well below their glass transition temperature (T-g) but the enzyme was fairly stable in rubbery trehalose systems. However, at moisture contents which allowed trehalose crystallization rapid thermal inactivation of invertase was observed. Invertase inactivation in heated PVP, MD and trehalose systems of reduced-moisture could not be predicted on the basis of glass transition and this was particularly true for trehalose. Conditions which would allow collapse of the systems and crystallization of trehalose were fairly well predicted based on the estimated T-g of model systems.