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.