THESIS

1.2.10 Crystallinity of RS III
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X-ray diffraction patterns of native high amylose rice starch and
RS III samples (0 to 48 hr pullulanase hydrolysis of 75 o C and 121 o C preheated high
amylose rice starch) are shown in Figure 21 and 22. The diffraction pattern obtained
from native high amylose rice starch was classified as an A-type pattern as indicated
by typical peaks at 15.0, 17.5 and 23.2 o of diffraction angle 2θ, with 13.18 %
crystallinity (Figure 20). These values are in agreement with those reported for native
rice starch and cereal starches. Ornanong et al. (2006) reported that the X-ray
diffractogram of the native rice starch showed an A-type crystal pattern with strong
reflections at 14.9, 17.8 and 22.8 o of diffraction angle 2θ for all strains of rice.
When the starch was subjected to debranching
retrogradation
treatments in this study, the 0, 16 and 48 hr pullulanase hydrolysis
treatments showed completely
different pattern from the native high amylose rice
starch. The RS III sample from 0 hr hydrolysis exhibited very low crystallinity values
due to the loss of crystallinity during thermal treatment, and the calculated
crystallinity was only 2.58 %. This result suggests that the stored starch contained
amorphous region than crystalline region. The RS III formation from 16 and 48-hr
hydrolysis of 75
ted to
debranching and retro
o C preheated starch sample displayed a V-type diffraction pattern
with 10.67 % and 12.91% crystallinity, respectively. This was attribu
gradation which reorganized the structure of starch into a helical
complex to that of V-amylose (Cui and Oates, 1979). Occurrence of V-diffraction
patterns is caused by the presence of amylose and lipids in the starting material.
In addition, the X-ray diffraction profile (Figure 21) of the RS
III samples from 4, 16, 24 and 48 hr hydrolysis of 121 o C preheated starch showed
very strong V-type diffraction pattern, which had 14.37, 15.59, 15.80 and 19.50%
crystallinity, respectively. RS III samples from 48 hr hydrolysis of 121 o C preheated
rice starch gave the strongest diffraction peak at around 17 o 2θ and a few small peaks
, 22 o and 24 o at around 2θ values of 20 . This indicated that highly debranching and
o
retrogradation of high amylose rice starch influenced the crystalline structure.
and