THESIS

(-1 to 43 o C) on concentrated starch gels by DSC. They found that the mechanism of
starch crystallization (instantaneous nucleation followed by rod-like growth of
crystals) is the same over the whole range of temperature. Moreover, at higher storage
temperatures, a more symmetrically perfect crystalline structure is found. Biliaderis
and Zawastowski (1990) studied the effect of temperature on rigidity of 5 % (w/w)
amylose and 40% waxy maize starch gels. They observations further support the
notion that amylase gelation mainly involves rapid formation of double helical
junction zones upon cooling of amylose solutions, whereas a network-based structure
for amylopectin is established mainly as a result of separation of partially crystalline
structure.
4) Botanical sources of the starch
The botanical source is one of great importance for the
retrogradation of starch gels (Gudmundsson and Eliasson, 1993). They dose not
concern differences in amylase content, because it has even been observed in starches
with very similar amylase content. This indicates that structural differences found in
the amylopectin molecule may be the cause of differences in the recrystallization rate.
Amylopectin from cereal has also been shown to retrograde to a lesser extent than
pea, potato and canna amylopectin which has been attributed to shorter average chain
length in the cereal amylopectin (Kailcheusky et al. 1990). The structural differences
in cereal amylopectin as related to retrogradation can be related either to differences
in the amorphous regions or to differences in the ratio of short to long chains and the
ratio of A-chains to B-chains. A greater amount of short chains over 15 glucose units
and increase ratio of A- chains to B-chains probably promote retrogradation. It has
also been reported that very short chain (6-9 glucose units) can inhibit or retard
retrogradation of starch gels (Levine and Slade, 1986)
2.6.2 Method used for estimating retrogradation
Retrogradation has been studied using analysis methods of different
techniques such as X-ray diffraction (Gidley and Bulpin, 1987), differential scanning
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