During freezing of starch gels, starch-rich regions are formed in
the matrix, where water remains partly unfrozen. High solid concentration
in the regions assists connection of the starch chains
resulting in thick filaments, whereas water molecules convert into
ice crystals and a separate phase is formed. Upon thawing, ice
converts to a bulk phase water and releases easily from the polymeric
network. This process is known as syneresis (Yuan &
Thompson, 1998). The freezeethaw stability (syneresis) of the
samples is presented in Fig. 3. In the absence of acetic acid, the
syneresis of both samples increased with increasing numbers of
freezeethawing cycles. The syneresis of the PG starch increased
steadily (Fig. 3A) while a rapid increase in the syneresis of the
GCWS sample was observed after the first freezeethawing cycle
followed by a stabilization (Fig. 3B). The syneresis of PG starch was
initially 20.87% and slightly increased to 21.80% after five freezeethaw
cycles (overall 4.28% increase). For the GCWS starch, the
syneresis was 17.23% in the beginning which increased rapidly to
20.78% after the second freezeethawing cycle (17.08% increase).
Then, the syneresis increased only slightly from 20.78% to 21.03%
(1.18% increase) after the 2nd cycle. Overall, from the first to the
fifth freezeethawing cycles, the syneresis of GCWS increased
18.08%. Comparing the values obtained for the two samples, it is
clear that the PG had greater syneresis than GCWS starch. Nevertheless,
during the five freezeethawing cycles less changes in the
syneresis of PG was observed than the GCWS (4.28% vs 18.08%). The
higher syneresis values of PG starch compared to GCWS starch may
be related to its lower water absorption capacity, the absence of
starch granules and freedom of the starch molecules to interact
with each other during freezing of the starch gel. These factors are
likely to result in greater water loss during thawing. However, the
granules of the GCWS starch can retard rapid re-association of
starch molecules during freezing and uptake more water during
thawing resulting in less syneresis compared to PG starch (Chen &
Jane, 1994b).