Thermal resistance of β-galactosidase in dehydrated dairy model systems as affected by physical and chemical changes

The objective was to study the remaining activity of the enzyme beta-galactosidase in dehydrated dairy systems and its relationship with simultaneous chemical (i.e. non-enzymatic browning, NEB) and physical changes (structural collapse) at temperatures from 70 to 105 degreesC. The presence of milk proteins had a structure-stabilizing effect, which was not reflected by enzymic stabilization or NEB prevention. Although the remaining enzyme activity was correlated with physical and chemical changes in some of the systems exposed at 22% R.H., these changes were not parallel to the macroscopic changes in some of the anhydrous systems. The single lactose systems were highly collapsed at all the temperatures analyzed, but enzymic inactivation and NEB were dependent on the storage temperature rather than on the degree of collapse. Chemical and physical changes were not correlated to the remaining activity. Changes which occur at a molecular level may not be related to the changes at a supramolecular level (such as those derived from glass transition or collapse). (C) 2002 Elsevier Science Ltd. All rights reserved.