ABSTRACT
Introduction ........................................................................................................ 573
Materials and Methods ..................................................................................... 574
Materials ...................................................................................................... 574
Methods ....................................................................................................... 575
Spray Drying ...................................................................................... 575
Freeze Drying ..................................................................................... 575
Scanning Electron Micrographs ...................................................... 575
Differential Scanning Calorimetry .................................................. 575
Water Sorption and Time-Dependent Crystallization ................. 576
Results and Discussion ..................................................................................... 576
Physical Structure ...................................................................................... 576
Glass-Transition Temperature.................................................................. 576
Instant Crystallization Temperature ....................................................... 578
Time-Dependent Lactose Crystallization ............................................... 579
Conclusions......................................................................................................... 580
Acknowledgments ............................................................................................. 581
References ........................................................................................................... 581
Lactose, the characteristic milk sugar, is present in dairy-based products. Its
physical state is important for the stabilization of products during
processing and storage (Roos and Karel, 1991a; Slade and Levine, 1991).
Lactose in foods is often in an amorphous state, which is very hygroscopic.
Amorphous materials can be produced from a solution by rapid cooling or
removal of solvent water, e.g., by freeze drying, and spray drying. Different
drying methods produce amorphous materials with different physical
properties, e.g., in terms of particle size and structure (Saito, 1985) and their
thermal behavior may differ. Spray-dried lactose and milk powders are
widely used in the food industries. The physical and chemical changes of
lactose can be affected or controlled by the glass transition (Roos and Karel,
1990; Slade and Levine, 1991). Above the glass transition, increasing
molecular mobility and free volume result in endothermic changes in heat
capacity, which can be detected by differential scanning calorimetry (DSC)
(Roos and Karel, 1990; 1991a; 1991b). Lactose crystallization in dairy
products is controlled by glass transition and water content causing rapid
product deterioration.