ABSTRACT
Introduction ........................................................................................................ 495
Materials and Methods ..................................................................................... 496
Materials ...................................................................................................... 496
Drying Treatments ..................................................................................... 496
Moisture Equilibration .............................................................................. 497
Analytical Determinations........................................................................ 497
Statistical Analysis ..................................................................................... 498
Results and Discussion ..................................................................................... 498
Changes in Pectic Composition as a Result of Drying Treatment..... 498
Calorimetric Analysis................................................................................ 499
Mechanical Properties ............................................................................... 500
Conclusions......................................................................................................... 501
Acknowledgments ............................................................................................. 502
References ........................................................................................................... 502
Drying of fruits promotes water loss and changes in product phases and
components. In a simplified way, fruits can be considered as being made up
of two phases: the insoluble cellular matrix and the liquid phase containing
the water-soluble compounds inside cells or intercellular spaces. Water
distribution among phases changes during the drying process, depending
on the process conditions. Changes in soluble components and the insoluble
matrix can also occur. These phenomena affect molecular interactions in each
phase and so the final properties and structure of the product also.
Mechanical properties of dehydrated products are closely related to the
physical state (glassy or rubbery) of the phases (Roos et al., 1998) and to the
structure developed as a result of induced deformations in cells and
intercellular spaces and of ruptures in cell bonding. Previous studies
showed that the drying process induces changes in the pectic substances
because of the structural modification of the cell wall, which is also related to
textural changes in dehydrated products (Forni et al., 1986; Torreggiani et al.,
1998). Analysis of mechanical behavior related to product texture, glass-
transition temperatures, and changes in pectic fractions during fruit drying
may help understand the structural and quality changes that take place
during dehydration as a function of process conditions. The aim of this work
was to analyze the effect of drying conditions (vacuum impregnation
pretreatment, MW application, and air temperature) on structural changes
that took place in apple. In this sense, the analysis of changes that occurred in
the structural polymers (pectic fractions), mechanical properties of dried
products, and glass-transition temperature of the soluble solid fraction of the
fruit was carried out as a function of moisture content.
