The results of intrinsic viscosity are given in Table 1. The intrinsic
viscosity value of the un-gelatinized N starch was 174.08 mL/g
that reduced significantly to 131.61 mL/g after cross-linking. Similar
results were reported by Majzoobi et al. (2009) and Majzoobi
et al. (2012b) for N and CL wheat starches. This can be related to
the reduction in the distance between the starch molecules and
formation of more compact molecules with lower hydrodynamic
volumes after cross-linking. Such molecules may have less friction
with the surrounding solvent and other molecules in the solution
and hence show lower intrinsic viscosity values. Addition of organic
acids, significantly reduced the intrinsic viscosity of the N and CL
starches. Reductions of 12.35% and 29.95% in the intrinsic viscosity
value were obtained after addition of AA and LA to the N starch,
respectively. For CL starch, reductions of 1.57% and 5.93% in the
intrinsic viscosity were obtained after addition of AA and LA,
respectively. Therefore, CL starch was more resistant to the acids.
It was noted that the gelatinized samples had significantly lower
intrinsic viscosity value compared to the un-gelatinized counterparts.
It is possible that the gelatinization process caused
some changes to the molecular conformation resulting in the decrease
in the intrinsic viscosity. Similar results were reported by
Majzoobi et al. (2012b). The intrinsic viscosity of the gelatinized
starches reduced further after addition of AA and LA. The results
would signify that the organic acids used in this study could probably
degrade starch molecules before and after gelatinization. Such
effect was more pronounced after gelatinization process. Before
gelatinization starch molecules are in semi-crystalline order within
the intact granules and hence the access of the acids to the starch
molecules is rather difficult. After gelatinization, the starch molecules
are essentially in the amorphous form and mostly amylose
may leach from the granules into the surrounding area (Tester,
Karkalas, & Qi, 2004) that would increase the possibility of interactions
between starch molecules and acids. Therefore, lower intrinsic
viscosity values were obtained for the samples after
gelatinization. Similar findings were reported by Majzoobi et al.
(2012a) for addition of L-ascorbic acid to the gelatinized wheat
starch.
Less reduction in the intrinsic viscosity of the CL samples as affected
by the acids may indicate that the CL starch was more resistant
to the acids compared to the N starch. In addition, LA had
greater effects than AA on both N and CL starches before and after
gelatinization. This can be related to the lower pH value of the
samples containing LA (i.e. pH = 3.34) compared to those with AA
(i.e. pH = 4.24). Comparable results were stated by Sriburi et al.
(1999) and Hirashima et al. (2005) for cassava and corn starches
after addition of different organic acids. Hirashima et al. (2005)
indicated that the intrinsic viscosity was mainly affected by t