ABSTRACT
Materials and Methods ..................................................................................... 604
Materials ...................................................................................................... 604
Samples Preparation.................................................................................. 604
Compression of Powders.......................................................................... 605
DSC Measurements ................................................................................... 605
DMTA Measurements ............................................................................... 605
Statistical Significance ............................................................................... 605
Results and Discussion ..................................................................................... 606
Mobility around the Glass Transition..................................................... 606
Mobility within the Glass ......................................................................... 606
Conclusion .......................................................................................................... 610
References ........................................................................................................... 610
Low moisture biopolymer-based systems are commonly encountered in
food (e.g., cereal products) or nonfood applications (e.g., packaging films,
pharmaceutical excipients). Obviously, understanding the physical basis of
their quality or performance over time or as a function of their composition
(water or other added solutes) is of primary importance. For several years, a
polymer science approach based on physical state, phase transitions, and
molecular mobility has been applied to investigate these aspects. Contrary to
the data generally found in literature, in recent years several quality or
property changes of biopolymer-based materials (Attenburrow et al., 1992;
Nicholls et al., 1995; Roudaut et al., 1999b; Grattard et al., 2002; ) have been
observed while the samples were still in the glassy state. As an example,
baked or extruded cereal products that are mostly amorphous as a result of
their hydrothermal process exhibit, following moisture pickup, texture
changes (Valles Pamies et al., 2000) below their glass-transition temperature
(T
). Structural relaxation (evolution of the material towards thermo-
dynamic equilibrium) and secondary relaxations of the material (localized
motions of the polymer chains) are signs of possible evolutions within the
glass.
