Occurrence, of starch

The starch in plants occurs in small microscopic granules that have a core of starch surrounded by a network of protein. In the granules, amylopectin has an orderly crystalline structure, whereas amylose is somewhat amorphous. The orderly structure of the starch molecules may impair digestion by pancreatic amylase. The occurrence of starch in granules, whether in wheat, potatoes, bananas, or other foods, may prevent the digestion of up to 50% of the starch in these foods... 

Starch, the general storage product in plant cells, is found also in lichen algae. The occurrence of starch in lichens was discussed in detail by Geitler (1933) on the basis of light microscope observations. With the electron microscope large starch plates were found in the Trebouxia of Physcia aipolia (Brown and Wilson, 1968) while Jacobs and Ahmadjian... 

One of the most abundant biopolymers available in nature is starch. Starch is a polysaccharide consistent of glucose monomers and is found in all green plants. Next to its occurrence in food and its use in food-related industries, the major application of starch is in the paper industry, followed by the adhesives industry. 

Figure 5.15 Scanning electron micrographs of starch granules after mild a-amylolysis showing the occurrence of spherical bl ocklet-l I ke structures, (a) potato and (b) wheat starch granules. (Adapted with permission from reference 1)...

The /3-amylase liberates the maltose in the /S-configuration. This is no proof for the occurrence of /3-D-glucosidic linkages in starch. On the other hand, it is not known why the /3-amylase, in contrast to the a-amylases, causes an inversion of the configuration. 

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