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Starch composition and structure.pptxdsfghnbvcxZZx
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- 2. THE STARCH MOLECULE Starchis polysaccharide made up of hundreds or even thousands of glucose molecules joined together. The molecules of starch are two general types, called fractions: amylose and amylopectin
- 3. • is along chain-like molecule, sometimes called the linear fraction, and is produced by linking together 500 to 2,000 glucose molecules. The amylose fraction of starch contributes gelling characteristics to cooked and cooled starch mixtures. A gel is rigid to a certain degree and holds a shape when molded. AMYLOSE
- 4. • Amylopectin hasa highly branched, bushy type of structure, very different from the long string- like molecules of amylose. In both amylose and amylopectin, however, the basic building unit is glucose. Cohesion or thickening properties are contributed by amylopectin when a starch mixture is cooked in the presence of water, but this fraction does not produce a gel. AMYLOPECTIN
- 5. Most natural starchesare mixtures of the two fractions. Corn, wheat, rice, potato, and tapioca starches contains 24 to 16 percent amylose, with the remainder being amylopectin. The root starches of tapioca and potato are lower in amylose content than the cereal starches of corn, wheat, and rice.
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- 7. In the storageareas of plants, notably the seeds and roots, molecules of starch are deposited in tiny, organized units called granules.
- 8. Amylose and amylopectinmolecules are placed together in tightly packed, stratified layers formed around a central spot in the granule called the hilum. The starch molecules are systematically structured in the granule to form crystalline-like patterns.
- 9. If the starchgranules in a water suspension are observed microscopically under polarized light, the highly oriented structure causes the light to be rotated so that a Maltese cross pattern on each granule is observed. This phenomenon is called birefringence.
- 10. The pattern disappearswhen the starch mixture is heated and the structure disrupted. The sizes and shapes of granules differ among starches formvarious sources, but all starch granules are microscopic in size.
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