ABSTRACT
Introduction ........................................................................................................ 689
Materials and Methods ..................................................................................... 690
Results and Discussion ..................................................................................... 691
Conclusions......................................................................................................... 693
Acknowledgments ............................................................................................. 694
References ........................................................................................................... 694
The physical state of foods, including sugars and biopolymers, has received
increasing attention because of its importance to food processing and storage
(Roos and Karel, 1991a). In Food Polymer Science, one of the most important
events used to characterize the physical state is the glass transition, which
involves transition from a “glassy” solid to a “rubbery” liquid-like state
(Roos and Karel, 1991a; Slade and Levine, 1991). This change occurs within a
temperature range characteristic for each material and the mid-point
temperature of such change is taken as the glass-transition temperature
(T
). Because there is a great increase on molecular mobility across T
, it is
hypothesized to be an important parameter for storage stability and quality
of dried or frozen products (Zeleznak and Hoseney, 1987; Inoue and
Ishikawa, 1997). For frozen food, another important property is the T
of the
maximally freeze-concentrated matrix (T
). The minimal moisture content at
which T
is visible corresponds to the unfreezable water content (X
). When
submitted to slow freezing, the system will consist of ice crystals embedded
in an amorphous glass matrix with a characteristic glass/rubber transition
temperature, T
, above which it begins to lose quality (Slade and Levine,
1991). The breakdown of structure above a “collapse” temperature (related
to T
) during freeze-drying is considered a major contributor to product
quality deterioration (Anglea et al., 1993).
