3.6. Turbidity of the samples
The results of turbidity determination of the samples during
storage time are given in Table 4. Similar to other starch gels, the
turbidity of both samples increased with increasing the storage
time (Bello-Pérez et al., 2000). This has been related to the increase
in the re-associations and re-organization of the starch molecules,
granule remnants aggregation, intra- or inter-bonding between
starch molecules as well as non-starch components such as lipids
and proteins (Mua & Jackson, 1997; Sandhu & Singh, 2007).
The results showed that the turbidity of the samples reduced in
the presence of acetic acid. Degradation of starch molecules in the
presence of acetic acid and hence formation of smaller starch
molecules can increase the transmitted light resulting in less turbid
gels. Similar findings have been reported for PG starches as
affected by L-ascorbic acid (Majzoobi et al., 2014b). The PGWS produced
more turbid gels than PGCS which may indicate higher sensitivity
of PGWS to retrogradation during storage, while the higher
fat and protein content of the PGCS may obstacle starch retrogradation.
Starch molecular size and chain length also affect gel turbidity.
It is possible that the PGCS had smaller size molecules
due to the lower pH of this sample at various concentration of
acetic acid leading to more clear gel. Further studies are required
to determine the starch molecular size and structure after pregelatinization
and acetic acid addition in relation to gel turbidity.