The rheological properties of corn and potato starch concentrated aqueous
solutions were investigated at 25?C. The starches were previously dispersed
in water and the solutions were obtained by heating of dispersions at
115-120?C for 20 minutes. The solutions of potato starch were transparent,
while the corn starch solutions were opalescent. The results of dynamic
mechanical measurements showed that the values of viscosity, h, storage
modulus, G?, and loss modulus, G?, of the corn starch solutions increased
with the storage time. This phenomenon was not observed for the potato starch
solutions. It was assumed that the increase of h, G? and G? is the result of
starch solutions retrogradation. The potato starch solutions retrogradation
did not occur probably because of the phosphates presence. The viscosity of 2
mass % corn starch solution is less than the viscosity of 2 mass % potato
starch solution. By increasing the concentration of corn starch solution the
gel with elastic behavior was formed. The corn starch solutions formed gel as
early as at 4 mass % concentration, while potato starch solutions achieved
the gel state at the concentration of 5 mass %. The value of exponent m (G?
and G? ? wm) during the transition of potato starch solutions to gel is
0.414, which gives the fractal dimensions for corn starch of 2.10. The
obtained value of fractal dimension corresponds to slow aggregation. The corn
starch solutions with the starch concentrations higher than 4 mass % form
weak gels. For these solutions the values of modulus in rubber plateau were
determined. It was found that the modulus in rubber plateau increased with
the concentration by the exponent of 4.36. Such high exponent value was
obtained in the case when the tridimensional network is formed, i.e. when
supermolecular structures like associates or crystal domains are formed.
Thermal and Rheological Properties of Agaropectin Aqueous Solutions
