4. Conclusions
In this paper the range of the transition glass temperature and
the microstructure of hard candy honey flavored have been investigated.
The glass transition temperature of hard candy honey flavored
was calculated and its influence on cooling process and
storage was also analyzed.
By applying DSC technique, it has been determined that the
glass transition temperature range for hard candy honey flavored
was 35.36 ± 1.48–36.37 ± 1.63 C. From product quality point of
view, the glass temperature (Tg) is important to determine the
cooling operating conditions in order to obtain adequate temperature
leaving the cooling tunnel. The maximum outlet temperature
at the center of each hard candy article is 34 C to reach the glassy
structure. Also, Tg is important to determine the storage conditions,
in order to avoid crystallization problems and therefore improve
product shelf life.
On the other hand, SEM images revealed undesired characteristic
like the presence of trapped air within the candy matrix. The air
content detected within the structure was 5.71 ± 1.72%, which produced
a decrease in the value of the thermal conductivity obtained
by Choi and Okos’s correlation from ke = 0.2821 ± 0.0141 to
0.2729 ± 0.0044 W/m C. However, it was concluded, that the thermal
conductivity of hard candy honey flavored is not significantly
affected by the presence of entrapped air within the matrix, due to
the fact that this decrease is within the standard error of the correlation
used.
In addition, with the help of SEM technique it was also observed
overlapping of layers at samples edges showing a hygroscopic
behavior which is one of the major responsible of the problem of
ageing.
DSC and SEM techniques provided useful and necessary knowledge
about the relationship among the microstructure, thermal
properties, composition (in particular moisture) and processing aspects,
especially at cooling stage and product storage. It is clear
that glass transition temperature serves as a guide for quality aspects.
Finally, the gained knowledge can be efficiently used not
only to ensure a high product quality but also to develop a mathematical
model to optimize the whole candy process. For instance,
the Tg value determined in this paper can be used as upper bound
on the outlet temperature at the cooling tunnel. Moreover, proper
assumptions to derive mathematical models can be considered
from the obtained results. For example, to neglect the effect of
air bubbles on the calculation of the candy thermal conductivity
obtained at the same processing conditions.