THESIS

(O’Dea et al. 1981, Jenkins et al. 1982, Bornet et al. 1989, Granfeldt et al. 1992 and
Englyst et al. 2003). The rate and extent of starch digestion is influenced by many
intrinsic food factors. Starch consists of two glucose polymers; amylose amylopectin.
The physical arrangement of amylose and amylopectin in food and their interaction
and/or interconnection with other food component (protein, lipids and fibre)
determine the physicochemical and functional properties of starch and is susceptibility
to amylolytic enzymes, and thus its bioavailability. Hydroyhermic food processing
has a major impact on starch availability (Bjorck, 2000). The arrangement of starch
components changes continuously under the influence of hydrothermic parameters
during both food processing and storage.
6.3.2 The role of starch sources and starch granule on low GI food
Common food starch is derived from seed (wheat, maize rice,
barley), roots (potatoes, cassava) and legumes (pea, lentils, mungbeen). Native starch
in granule form is insoluble in cold water. Its microcrystalline structure gives rise to a
characteristic polarization cross under polarized light. Under dry heat conditions,
starch granules are not disrupted and the polarization cross remains unchanged.
Native starch granules are slowly attacked by salivary and pancreatic amylases.
Mechanical processes cause fissures to appear on the surface increase the
susceptibility of starch to α- amylase (Bjorck and Asp, 1984).
6.3.3 The role of gelatinized starch on low GI food
Starch is usually eaten after an initial gelatinization step. Dramatic
changes occur in the structure of the starch granule when it is heated in the presence
of water are descried in above topic (2.4). Amylose content is not a discriminate
indicator of α- amylase susceptibility when starch is native (Bornet et al. 1989).
Tuber starches are highly resistant to amylase despite their low amylose content.
However, after gelatinization, amylose content becomes an important factor in
determining α- amylase susceptibility. It is explained by the marked tendency of high
amylose content starch to produce hard gels, retrograded amylose and amylose lipid
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