When citric acid was added before gelatiniza-
tion, the viscosity of cornstarch pastes increased by adjusting
the pH between 5.6 and 3.6, while the viscosity of pastes with
pH below 3.5 decreased further than that of the control (pH
)
6.3) on the steady shear and dynamic oscillatory measurements.
It is obvious from intrinsic viscosity measurements that the
hydrolysis of glucose chains occurs by adding acid before
gelatinization. However, increases in the viscosity could be seen
by adding small amounts of acids (5.6
>
pH
>
3.5), because
many glucose chains leached out from starch granules, indicating
that there were many entanglements of glucose chains. On the
other hand, adding large amounts of acids (pH
e
3.5) leads to
the fracture of starch granules, and thus, a decrease in the
viscosity was observed.
No decrease in the viscoelasticity was noted for cornstarch
pastes by adding citric acid after gelatinization. The hydrolysis
of glucose chains could be prevented.