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

Abstract

The thermal stability of a commercial preparation of neutral lactase ( -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 (T g ) 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.

Correlations between Molecular Mobility and Chemical Stability During Storage of Amorphous Pharmaceuticals

“…Variations in chemical stability that do not seem to be related to global mobility have also been observed for various solid proteins, including restriction enzyme EcoRI dried with sucrose, trehalose, maltodextrin or PVP, 104 lactase and invertase lyophilized with trehalose, maltose, lactose, sucrose, raffinose, maltodextrin, casein or PVP, 22,[105][106][107][108] and glucose-6-phosphate dehydrogenase lyophilized with dextran, sucrose or raffinose. [109][110] It is not easy to explain the lack of correlation between chemical stability and global mobility for proteins because of many complicated factors possibly affecting the chemical stability.…”

The measurement of the glass transition temperature of sucrose and maltose solutions with added NaCl

“…1 It has been suggested that below this temperature the high viscosity of the unfrozen glassy phase and the low diffusion coef®cients of species within this matrix provide conditions that lead to a marked decrease in the rate of reactions associated with food deterioration. 2 However, recent kinetic studies of chemical processes such as non-enzymatic browning, 3±5 oxidation of ascorbic acid, 6±8 enzymatic reactions, 9±12 colour stability, 13 aspartame degradation, 14 lactase stability, 15 starch retrogradation 16 and lipid oxidation 17 have produced results both for and against the importance of T g and the Williams± Landel±Ferry (WLF) kinetics associated with the expected changes in viscous properties.…”

Protective Role of Trehalose on Thermal Stability of Lactase in Relation to its Glass and Crystal Forming Properties and Effect of Delaying Crystallization

“…Although thermal stability of enzymes is expected to be related to mobility aspects, the influence of glass transition has not yet been fully demonstrated and the specific mechanism of enzyme protection observed in trehalose matrices can not be attributed entirely to the glass transition phenomenon (3). The extent of protection provided by poly(vinyl)pyrrolidone (PVP) and maltodextrin (MD) matrices on the thermal stability of invertase (3) and lactase (13) is somewhat related to their glass transition temperatures. However, even when the matrices are in the glassy state, the loss of enzymatic activity is important if the temperature is sufficiently high (3,13).…”

“…The extent of protection provided by poly(vinyl)pyrrolidone (PVP) and maltodextrin (MD) matrices on the thermal stability of invertase (3) and lactase (13) is somewhat related to their glass transition temperatures. However, even when the matrices are in the glassy state, the loss of enzymatic activity is important if the temperature is sufficiently high (3,13). Cardona et al (14) demonstrated that if sufficient water was present to allow crystalline trehalose dihydrate formation in a high proportion, the protective action of trehalose on invertase stability was lost.…”