4. Conclusions
The study revealed that the Page model can be used to predict
the drying behavior for the spouted bed drying of cubes formed
from carrageenan gels K12, K73, and their blends with carrageenan
92S (iota). Increasing the air temperature from 60 to 150 C lowered
the equilibrium moisture content, and thus the water activity,
increased specific energy consumption, and decreased the drying
time for all types of carrageenan gels by ca. 50%. Covering of
carrageenan cubes with powder obtained from the dried product
reduced their stickiness, allowing the formation of a proper
spouted bed in the first minutes of drying, but also extended the
entire time of drying by 10 min. The linear decrease of spouted bed
volume ratio versus moisture content during the drying of carrageenan
cubes was significantly affected only by the kind of material.
However, the final values of the bulk and apparent densities
depended on both the kind of material and the drying temperature.
The differences in the final values of the bulk and apparent densities
of dried carrageenan samples can be explained, taking into
account the effect of temperature and the material properties on
the mechanism of shrinkage, which was dominated by shape
deformation, rather than decreasing in a linear manner, beyond a
certain critical moisture content. The increase in drying temperature
enhanced the formation of a lighter color of dried product,
apart from the K73 þ iota samples, which remained dark. On the
other hand, our studies indicated that the drying of carrageenan
gels at 100 C provides a product with good solubility and high
gelling ability.
Taking into account all our results, we recommend spouted bed
drying of carrageenan gels at 100 C, recognizing K12 as the best
raw material for production of carrageenan powders, as it generally
had the best functional properties among all the samples tested.