Starch as a component in bread that contributes to staling.Starch is one of the major components which accounts for 70 to 75 percent of wheat flour. Various studies have been conducted which proved that the firmness of bread is affected by the changes in starch structure. The major constituents in starch are the 25 - 28 % amylose and 72 - 75 % amylopectin. Amylose is composed of a-(1,4)-linked D-glucopyranosyl units with very insignificant branches formed by a-(1,6)-linkages. Amylose molecule is practically considered to be linear. In contrast, amylopectin is comprised of 10 to 100 linear chain a-(1,4)-linked D-glycopyranosyl units and forms branch at a-(1,6)-linkages which generated up to 3 million glucose units of highly branched polysaccharide (Haegens n.d.). The gelatinization of starch involves both hydration and swelling of starch granules. Apart from that, disarrangement of amylopectin crystallinity with the disappearing of birefringence as well as the leaching of amylose from starch granules into solution are also parts of starch gelatinization. The gelatinization temperature of wheat starch is within 52°C to 64°C. In the preparation of bakery products like bread, complete starch gelatinization usually occurred during the production (Biliaderis cited in Lee & Lee 2012).
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Further swelling of granules, amylose dispersion into the moisture and increase in viscosity are the results of the continuous heating of starch granules in excess water after gelatinization (Lee & Lee 2012). Upon cooling, starch molecules orient and retrogate themselves while syneresis occur where watetr is removed from the molecules. There are amorphous and crystalline regions present in the starch granules. The term "amorphous" refers to the lack of a definite whereas "crystalline" which is opposite for amorphous which refers to a definite structure. When starch undergoes gelatinization, there is a change in the X-ray pattern or in the degree of crystallinity. On aging, the gels retrograde or undergo a change in structure which results in a different type of diffraction pattern. The evidences proving starch as the component in bread that causes staling was proposed by Katz (1928) stating that the retrogradation of starch polymer was responsible for bread staling as shown by the x-ray diffraction patterns of fresh bread which was similar to freshly gelatinized wheat starch, while the patterns of stale bread were shown to be similar to retrograded starch. This finding led to the important discovery of the gradual change in the starch components from amorphous to crystalline which contributes significantly in the staling process (Kartz cited in Gray & Bemiller 2003).
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