X-ray Diffraction Patterns. All starch samples showed the
typical A-type X-ray diffraction patterns of cereal starches as
shown in Figure 3. Except for IR74, the chalky kernel starches
noticeably showed more intense diffraction peaks compared with
translucent kernel starches, thus resulting in higher percent
crystallinity values for the chalky kernel starches (Table 5).
The direct relationship between crystallinity and amylopectin,
and the inverse relationship between crystallinity and amylose
were highly significant (Table 4). It appeared that the intensity
of X-ray diffractions was largely determined by total amylopectin
content but not by amylopectin structures because no
particular relationship could be significantly established between
amylopectin average chain length and crystallinity or between
amylopectin branch chain length distribution and crystallinity
(Table 4). These observations were in agreement with the report
of Tester and Karkalas (32) that there was no absolute
dependence of crystalline form on amylopectin structure,
especially chain length. The present results also indicated the
complex nature of the structural organizations within the starch
granule.