Starch grains structure

Czaja, A. T. (1978). Structure of starch grains and the classification of vascular plant families. Taxon T1,463 70. 

The starch grains are insoluble in water at room temperature. At 50-60 °C, starch absorbs water reversibly and hydrogen bonding is reduced. Above 60 °C (this temperature depends on the native source) the structure of the starch is modified irreversibly, crystallinity disappears and gelatinisation occurs. 

Structure and Composition of Starch.—Starch grains vary in shape from spheroidal to oval to chonchoidal to polygonal. They... 

Maize or Corn Starch.—The structure of a grain of maize is similar to that of a grain of wheat already described. The average analysis of maize is starch 55, other carbohydrates 15, proteins 10-5, fat 5, ash 2-5, water 12 per cent. Of the proteins present one is soluble in water, and the gluten is soluble in dilute caustic alkali. 

Figure 10.16. De-structuring of starch grains in an aqueous solution containing 40% formic acid observed under an optical microscope (OM) [FEL 05]...

Yasuda (1945) deduced this from his observation that the protoplasm of the pollen tube is found primarily at the apex and constantly recedes from the older portions of the pollen tube. Later, O Kelley and Carr (1954) observed from electron micrographs that the wall structure of the extreme tip was more open than the portions behind the tip. This has been confirmed by Iwanami (1959), who considers the tip to be continuously in an unfinished state. He presents evidence that the tube contents are always under slight positive pressure maintaining a continuous tendency toward rupture of the tip membrane, counterbalanced by the continuous formation of new wall. He also observed that the protoplasm at the very apex of the tube has a different appearance than that further back because of the absence of granules (starch grains). This clear portion he has called a cap block. 

Native starch cannot be treated as a traditional polymer because the arrangement of amylose and amylopectin leads to the already explained grain structure. As observed by Donovan [11] this grain structure has a melting process related to the amount of water contained in it. 

Thin section of a Rhodosorus cell, showing the chloroplast and other organelles. Various views of the phycobilisomes can be seen due to the angles at which different thylakoids have been sectioned. Plug-like structures are visible in the inset (circle), c = chloroplast m = mitochondrion n = nucleus p = pyrenoid s= starch grain. 

Swelling food starches that passed water and thermal treatment, get new structure, i.e. there is a sphtting of polysacharide starch grains. 

In their original classic work. Brown and Morris observed that hydrolysis of starch grains never takes place if the enclosing endosperm cells walls are intact. About the same time as a-amylase is released from the aleurone layer, there is also the release of an endo-jS-glucanase, the mode of action of which is purported to include the dissolution of the endosperm cell walls as well as the cell walls of the intermediate layer. The action of this enzyme, however, has not rigorously been determined in relation to the structure of the endosperm or intermediate layer cell walls themselves, though it has been reported that... 

This section is followed by another extensive discussion of starch, the other major commercial polysaccharide. It is amazing how much difference a simple stereochemical variation can make in the structure and properties of a macromolecule. Even more fascinating patterns are observed in native starch grains. The crystalline fibrils are arranged in a fractal-like pattern called trichites (Fig. 3.14). 

Chapter 52 - It is directly observed a variety of morphologies of the cereal starch nano-structural units after the heating gelatinization by using atomic force microscope in the atmosphere. According to the observation results, nano-structural units of starch grains can be... 

Fig. 2.2. Structure of parenchymatous plant cells. A. Cell from the petiole of a sugar-beet leaf. It has vacuolated cytoplasm with mitochondria, chloroplasts and nucleus. B. Starch sheath cells from young stem of tobacco, showing prominent starch grains in the chloroplasts. (Both xll90.) (From K. Esau, Plant Anatomy, John Wiley Sons, Inc., New York, 1953.)...

Fig. 2.17. Bottom left. Chloroplasts (P) in chlorenchyma of pea leaf. Note the large starch grains within the chloroplast (asterisks). IS, intercellular space V, vacuole. X 780. Right. Electron micrograph of a chloroplast of a leaf of spinach Spinacea oleracea). The chloroplast is surrounded by a double membrane (PM) and the internal membrane system is differentiated into grana (asterisks) and stroma lamellae (open arrows). Osmiophilic droplets (small black arrows) occur in the plastid stroma. The structure of the grana is shown in more detail in the inset top left) as are regions of continuity between the grana and stroma lamellae (large solid arrows). Key CM, cell membrane CW, cell wall SG, starch grain ...

When starch is heated in water to 60-80°C the starch grains swell and yield two components. One component (amylose) is water-soluble, is entirely degraded to maltose by the ]S-amylase and its molecules consist of unbranched spiral chains of glucose units (300-1000 units) linked by 1 4 a-linkages. The second component (amylopectin) is not soluble, yields both maltose and dextrin on treatment with )8-amylase and has a branched chain structure due to the occurrence not only of 1 4 but also of 1-6 linkages between the glucose units (Fig. 5.11). 

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