Doctor of Philosophy / Department of Grain Science and Industry / Yong-Cheng Shi / Starch is the most important source of food energy. However, the information about the
metabolic quality of starchy foods is scarce. It is well known that native starches with a B-type
X-ray diffraction pattern are more resistant to alpha-amylase digestion than those starches with
an A-type X-ray pattern, but the underlying mechanism is not well understood. It is not clear
whether the enzyme resistance of B-type starch is due to its B-type crystalline structure or the
other structural features in starch granules. The objective of this study was to compare the
structure and enzyme digestibility of highly pure A- and B-type starch crystals, and understand
the roles of crystalline types in starch digestibility. Highly pure A- and B-type starch crystals
were prepared from short linear α-glucans (short-chain amylose) generated from completely
debranched waxy starches by manipulating the processing conditions such as starch solids
concentration, crystallization temperature and chain length. High concentration, high temperature
and short chain length favored the formation of the A-type structure, whereas reverse conditions
resulted in the B-type polymorph. Digestion results using a mixture of α-amylase and
glucoamylase showed that A-type crystals were more resistant to enzyme digestion than B-type
crystals. The A-type crystalline product obtained upon debranching 25% waxy maize starch at
50ºC for 24 h gave 16.6% digestion after 3 h, whereas B-type crystals produced by debranching
5% waxy maize starch at 50ºC for 24 h followed by holding at 25ºC for another 24 h had 38.9%
digested after 3 h. The A-type crystals had a higher melting temperature than the B-type crystals
as determined by differential scanning calorimetry. Annealing increased the peak melting
temperature of the B-type crystals, making it similar to that of the A-type crystals, but did not
improve the enzyme resistance. The possible reason for these results was due to more condense
packing pattern of double helices in A-type crystallites. It seems that the crystalline types are not
the key factor that controls the digestibility of native starch granules. The resistance of native
starches with B-type X-ray diffraction pattern is probably attributed to the other structural
features in starch granules.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/15323 |
| Date | January 1900 |
| Creators | Cai, Liming |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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