THESIS

in excess water. The loss of birefringence occurs over a broader temperature interval
when content is decreased (Lund, 1984).
2.5.3 Loss of crystallinity
The loss of crystalline order during heating is observed by X-ray
diffraction. The diffraction pattern disappears, and eventually a pattern indicative of a
completely amorphous material is obtained (Zobel et al. 1988). The temperature range
during which the crystallinity is lost and the rate which it is lost depend on the water
content and or the type of starch (Liu et al. 1997). The temperature range increases
with decreasing water content, and at water content below 50% the temperature for
complete loss of crystallinity approaches 100 o C. The loss of crystallinity seems to
occur in two steps: at first the loss occurs at a very low rate, but then at a temperature
typical of the starch the rate increases dramatically (Svensson and Eliasson, 1995).
Tester et al. (1994) indicated that low and high gelatinized
temperature (GT) starches had very similar amylopectin chain lengths after
debranching and on debranching of insoluble residues after lintnerizaton. The low GT
starches could be annealed to behave like high GT starches, but the latter also
responded a little to annealing. It was concluded that low GT starches have less
crystallinity and less perfect crystallites than the high GT starches due to minor
amylopectin structural differences. Eliasson et al. (1980) reported that amylopectin
branch chain lengths and distributions determine starch GT, enthalpy change, and
pasting properties. Starch GT increased with increasing branch chain length.
2.5.4 Endothermic transitions
The starch gelatinization is an endothermic process with enthalpy
values in the range 10-20 J/g. During the last 10 -15 years DSC has become the most
important tool for studying starch gelatinization (Donaovan, 1979; Eliasson, 1980).
DSC measures the gelatinization transition temperature and the enthalpy of
gelatinization (∆H). These DSC parameters are influenced by the molecular
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