THESIS
THESIS
THESIS
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value than the waxy rice flour gel. However, they found that during the first cycle the<br />
amylose rice flour gel had changed from a smooth gel to a rough- textured porous gel<br />
(rough surface) with a sponge-like structure that allowed it to reabsorb the separated<br />
water. Thus, syneresis was not detectable unless this rough-textured gel pressed to<br />
squeeze out the absorbed water. This retrogradation phenomenon occurred when the<br />
starch gel was frozen and ice crystals spread within the gel. Upon subsequent thawing<br />
at a lower temperature (30°C), the ice crystals melted and a rough porous gel was<br />
formed and it was not enough to form a spongy structure and a high syneresis value<br />
was observed. From the second to the fifth cycle, the quantity of rough-textured gel<br />
accumulated curve indicated the formation of a rough and porous gel alter thawing<br />
and it formation of a rough and porous gel after thawing and it confirmed the very low<br />
freeze-thaw stability of this flour. When thawed at higher temperature (60°C, 90°C<br />
and microwave), amylose rice flour gels no longer formed a rough, spongy gel<br />
because of re-dissolved of retrogradation starch during heating.<br />
5.3 The mechanisms of RS III formation during drying of the starch<br />
The drying of recrystalized resistant starch may be performed at room<br />
temperature or at elevated temperatures. Thus, the recrystalized retrograded starch<br />
may be cooled from the crystal-propagating temperature to room temperature or to a<br />
drying temperature which is above room temperature. Exemplary drying temperatures<br />
may range from about 20°C. to about 130°C., depending on mode of drying,<br />
preferably from about 45°C. to about 80°C., for oven-drying. Known drying methods<br />
for the drying of starch, which do not substantially destroy or melt the crystals of<br />
resistant starch type III, may be employed. Exemplary drying methods which may be<br />
used include freeze-drying, oven-drying, vacuum-drying, spray drying, flash-drying,<br />
belt-drying and drum-drying. The drying of the high-melting-point resistant starch<br />
type III composition is conducted to achieve a shelf-stable water activity or relative<br />
humidity of less than about 0.7. The water content of the dried product may<br />
approximate that of commercially available flour. Exemplary moisture contents of the<br />
dried, bulking agent or flour substitute or replacer may range from about 8% by<br />
weight to about 14% by weightb (Relinda, 1994).<br />
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