Carbohydrates in Amorphous States: Molecular Packing, Nanostructure, and Interaction with Water

The last few decades have witnessed a considerable impact of the study of phase transitions in carbohydrate - based systems on the prediction and optimization of product stability and shelf life in low - moisture foods and pharmaceutics. Such studies have in particular been aimed at the analysis of the glass transition and the role of water as a plasticizer. There is a growing awareness, however, that a number of issues cannot be resolved satisfactorily without an understanding of the molecular physics of carbohydrate matrices. This includes the properties of carbohydrate glasses, the phase behavior and molecular structure of carbohydrate - water systems, and the understanding of the role of carbohydrates as bioprotectants. In this chapter, an overview is provided of recent advances in the molecular physics of carbohydrate matrices, including our own work on the elucidation of the carbohydrate nanostructure by positron annihilation lifetime spectroscopy (PALS) and molecular dynamics (MD) simulations. The implications of these fi ndings for the development of encapsulation systems and bioprotectants are discussed.