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