THESIS

of RS overall, 60%, among the three enzyme combination, followed by α-amylase-
pullulanase, then α-amylase alone.
The amount of resistant starch can be increased by enzymatically digesting
rapidly digesting starch followed by washing/filtration to remove short chain low
molecular weight sugars. Crystallization of all crystallisable substances involves three
sequential steps, namely: 1) nucleation – formation of critical nuclei; 2) propagation–
growth of crystals from nuclei by intermolecular association; and 3) maturation–
crystal perfection and continued slow growth (Wunderlich, 1976). Nucleation is
favoured at lower temperatures, while propagation and maturation favour higher
temperatures. In retrograded wheat starch gels, low temperature storage (at 5 and 4 o C)
has been shown to result in recrystallization to lower Tm, less symmetrically perfect
polymorphs than those produced by storage at room temperature. Higher
crystallization temperature favours formation of the higher Tm, more stable A-type
polymorphs. These probably form the resistant starch fraction (Seib and Woo, 1999).
Hizukuri et al. (1983) also reported that isoamylase and pullulanase
degraded potato amylose rapidly at the beginning and then approached constant
values on prolonged incubation with large amounts of enzyme. Debranching nonwaxy
starch and waxy starch with a higher concentration of enzyme results in higher
amount of slowly digestible starch and resistant starch after 2-4 hr of debranching and
a subsequent decrease at longer debranching times.
The differences in the amount of debranching are affect the retrogradation
process during storage. The degree of retrogradation depends on starch precipitation
or aggregation and gelation. Gidley and Bulpin (1989) described these processes in a
phase diagram showing the effect of cooling aqueous solution of synthetic amylose.
In general, precipitation was favored by shorter chain lengths and gelation is favored
by longer chain lengths. Guraya et al. (2001a) observed that debranched waxy starch
formed white milky precipitates on cooling while non-waxy debranched starch
formed a white gel with a fat-like consistency.
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