3.7. Syneresis of the samples
Physical changes during freezing and thawing of starch gels
known as syneresis are related to the starch ability to hold water and its tendency for retrogradation. Fig. 2A and B shows that the
syneresis of both samples increased with addition of acetic acid.
On the other hand, the samples released more water after subsequent
freeze thaw cycles. Formation of smaller starch molecules
as a result of acetic acid addition can reduce water absorption of
the samples as observed previously (see Table 2). Therefore, the
starch molecules could not hold as much water resulting in more
syneresis of the samples.
It was also noted that the overall syneresis of PGWS ranged
from 17.23% to 25.23% (46.43% increase) while that of PGCS varied
between 20.87% and 32.67% (56.54% increase). Therefore, in the
presence of acetic acid, PGWS gels were more resistant to freeze–
thaw cycles compared to the PGCS gels. This can be related to
the larger molecular size of PGWS which results in its higher water
uptake and stronger gel network compared to PGCS (see also
Tables 2 and 3). Similarly, a significantly negative correlation
between swelling power and syneresis of rice starch obtained from
different rice cultivars has been reported, but no correlation was
observed between amylose content and syneresis of these samples
(Sathaporn Srichuwong, Isono, Jiang, Mishima, & Hisamatsu, 2012).