THESIS

Figure 9 Schematic diagram showing the process occurring the gelation and
retrogradation of amylose and amylopectin
Source: Wilson et al. (1987)
Cereal amylose may form double-helical associations of 40-70
glucose units, while amylopectin forms shorter double helices (Miles et al. 1985a;
Goodfellow and Wilson, 1990; and Liu et al. 1997). The latter can be attributed to
restrictions imposed by the branching structure of the amylopectin molecules and the
chain lengths of the branches, Thus, amylose, is responsible for short-term changes
while amylopectin is responsible for the longer term rheological and structural
changes of starch gel. Double helices may associate and organize into crystallites,
most of which are related to association of the amylopectin chain which comprise the
bulk of the starch component of rice. The retrogradation of maize amylopectin was
proportional to the amount of short chains having a DP of 16-30 and inversely
propolytional to the level of short chains with a DP of 6 – 11 (Shi and Seib, 1995).
Lu et al. (1997) studied the retrogradation of amylopectin from
Taiwan rice varieties. They reported that the short chains of amylopectin with DP 10 -
15 glucose units would result in more retrograded crystalline building blocks. On this
basic as well, it would require more energy to disorder the greater number of double
helical linkages of retrograded amylopectin. Thus, the plateau enthalpy would be
higher (Sander et al. 1990). Gidley and Bulpin (1987) suggested that a chain length of
at least 10 units is required for crystallinity development and, by inference, for the
formation of double helices. On the other hand, short chains with DP 6-9 glucose
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