THESIS

amylose is the linear fraction of starch. Commercial samples of amylose usually occur
in retrograded, water insoluble form, which can be solubillized by pressure cooking at
150-160 o C. On cooling, amylose solutions of 2% or higher concentrations, prepared
in this way, rapidly gel, while at concentrations lower than 2% precipitation occurs
(Schoch, 1964). Amylose is also soluble in dilute alkali, and rapid neutralization of
concentrations greater than 2% results in gel formation. Both the gelation of amylose
from concentrated solutions and precipitation from dilute solution can be termed
retrogradation. The gels and precipitates formed result from the inherent tendency of
amylose molecules to undergo conformational ordering and to tendency of amylose
molecules to undergo conformation ordering and to subsequently align or aggregate
(Gidley and Bulpin, 1989). The rate of retrogradation increases with increasing
amylose concentration and with decreasing temperature and is greatest at pH 5-7. In
addition, the retrogradation rate has a sharp maximum at amylose degree of
polymerization (DP) of 80, shorter and longer molecules being much more soluble
(Ring et al. 1987 and Jacobson et al. 1997).
Goodfellow and Wilson (1990) studied the retrogradation of
amylose using Fourier Transform Infrared (FT-IR). They found that helix formation
must occur before the creation of crystallites; therefore double helix must form at the
short or early on in the gelation process. Thus in summary, a same time as phase
separation, to create a gel network, with subsequent aggregation of these helices
producing crystallinity would be consistent with the experimental data (Figure 9). The
IR results for amylopectin suggest an initial fast change followed by a much slow
change. Previous IR work by Wilson et al. (1987) in which the spectra for
amylopectin from 6 to 340 hour were obtained suggest that FT-IR and G´ monitor the
same process-namely the crystallization of the amylopectin side chains followed by a
slow aggregation of these helices to produce crystallinity (Figure 9) .
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