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Glass Transition and Thermal Stability of Lactase in Low‐Moisture Amorphous Polymeric Matrices

The thermal stability of a commercial preparation of neutral lactase (β‐galactosidase) in low‐moisture amorphous polymeric matrices of maltodextrin (MD dextrose equivalent (D.E.) = 10.9) and polyvinylpyrrolidone (PVP; MW 40 000) stored at various temperatures (T) was studied. The main objective was to analyze the usefulness of the glass transition temperature (Tg) as a parameter for predicting the thermal stability of lactase in low‐moisture glass‐forming matrices. Loss of enzyme activity was observed during storage in glassy conditions (either in PVP or MD matrices), suggesting that, although molecular mobility may be significantly decreased in the glassy state, the protein molecule is still mobile enough to lead to enzyme inactivation. The results indicated that the change from the glassy to the rubbery state of the PVP matrix, where the enzyme was embedded, was not reflected in drastic changes in the temperature dependence of the thermal inactivation rate, as expected if it could be only predicted on the basis of physical changes of the matrices. The plasticizing effect of water is not the only factor to take into account when considering enzymatic stability in heated low‐moisture amorphous systems.