3.6. Rheological properties
The rheological properties of the studied carrageenan samples
are compiled in Table 7. Drying at 150 C lowered the storage
modulus G0 of K12, K12 þ iota, and K73 þ iota gels after sol-gel
transition, but it did not affect the rheological properties of the
gels formed by K73. Drying at 100 C increased the value of G0 for
K12 gels compared to hydrocolloid dried at 60 C, but the value of
G0 was reduced for K12 þ iota. Drying K73 or K73 þ iota did not
change the G0 value compared to carrageenan dried at 60 C. Thus,
the lowering of the quality of carrageenan after drying at temperatures
above 80 C described by Thommes et al. (2007) was
confirmed only when the hydrocolloids were dried at 150 C.
Higher tolerance of SBD to increasing temperatures can be
attributed to the cooling effect of the drying air stream characterized
by higher speed, and consequently, more intense heat
exchange. Drying at 100 C can actually improve the rheological
properties of gels formed by some types of carrageenan compared
to treatment at 60 C. The higher values of modulus G' found for
K12 can be responsible for better structure-forming properties,
manifested by lower apparent density (Table 5) and porous texture
(Fig. 9), fixed due to the greater rigidity of the material, which
causes open spaces formed during the drying process not to
collapse while cooling.
Drying at different temperatures did not affect the temperature
of the beginning, T1, and the end, T2, of the sol-gel transition. Only
the iota additions to kappa carrageenans slightly reduced T2. Drying
K73 at 100 C caused a rise in temperature T1.