3.2. Microstructure and critical design parameters relationship
In the confectionary industry, several process operating parameters
are critical to produce high quality products. For this reason,
such parameters should be controlled. Also, the behavior of the
ingredients plays an important role on the product quality and
therefore should be considered.
3.2.1. Hygroscopic behavior
Specifically in hard candies manufacturing, hygroscopic properties
are closed related with the wrapping stage during processing
and the product storage. Also, the presence of air bubbles in hard
candy matrix could affect the performance of the cooling stage.
The problems mentioned above are analyzed in this section using
SEM as a tool to reveal the strength in the relationship between
the structure and properties.
SEM micrographs showing the microstructure of hard candy
honey flavored are presented from Figs. 4 to 9. In these figures, it
can be clearly observed the presence of supercooled material and
the glass-like structure.
The non-equilibrium state of amorphous materials has no characteristic
order of molecular arrangement, which has caused difficulties
in understanding their properties [1].
In supersaturated solutions, molecules or molecular groupings
tend to be in contact by short range forces. Once contact has been
established, they are attracted in one direction only, being free to
glide in any direction on the surface. When molecules move along
a projection, they form a layer front that continues until meeting
an angle. When this action is being repeated by the constant bombardment,
migration and attachment of fresh molecules from the
solution, the cumulative effect is visible by the advance of the layer
fronts [22], as can be seen in Figs. 4–6.
Fig. 4 illustrates a portion of the edge [E] and the center [C] of a
hard candy. Figs. 5 and 6 clearly show the overlapping of layers [OL]
at samples edges. This overlap between the edge and the center
may be attributed to the ageing of the hard candy, which is caused
by the water absorption from the environment, related with the
storage problems. The quality problem of ageing is due to hard handy
exhibits hygroscopic properties. Consequently for sucrose composition
less than 55% (in this case, sucrose composition is 39%),
sucrose dissolution and candy melting occurs due to moisture uptake
causing quality problems related to stickiness during storage
[12]. In the microstructural aspects, this phenomenon is observed
as the formation of a film with lower viscosity than the original
at the hard candy periphery, as is shown in Figs. 5 and 6.