The Source for Glucan Bio Info

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Starches are found in a very diverse array of plants, primarily in storage organs such as tubers and seeds. Starch is a major component of the "average" dietary intake of man and animals. Because of the presence of cyanogenic glycosides, not all starches are edible without cooking (eg. cassava). Starch can be gelatinized when heated as an aqueous dispersion.


Calculated in calories, about four-fifths of the worlds food is provided by three grain crops (maize, wheat and rice) and three tuber crops (potato, yam and cassava). On a dry-weight basis starch is by far the major component of the edible portions of these crops, providing between 60% to 90% of the dry weight.


As well as its uses in nutrition, starch is also an important component in manufacturing a wide range of industrial products such as paper, textiles and building materials. Furthermore, chemically modified starch and starch derivatives are used widely throughout industry. World-wide, maize represents the major commercial source of starch, whereas wheat starch is of only minor significance in the starch industry.


Starch plays a central role in metabolism in most higher plants since it serves as the plants major food reserve. It is deposited as water-insoluble granules as a mixture of amylose and amylopectin. In leaves chloroplasts, starch acts as a temporary store during photosynthesis where it is stored within a separate metabolic compartment that is termed the chloroplast. During the dark the starch is remobilized.


Longer-term storage takes place in the reserve organs during one phase of the plant's growth: the starch will be used at another time for germination. In cereal plants the starch is laid down in the endosperm tissue of the grain. In potato the storage organ is the tuber. In tomato, like many other fruits, starch is laid-down transiently before ripening, during ripening the starch is degraded back to sucrose. In plant storage tissues such as the developing cereal grain, the final stages of starch biosynthesis are confined to a separate metabolic compartment within the cytosol. This intracellular organelle is termed an amyloplast and consists of a starch granule surrounded by plastid stroma which is enclosed by a double membrane.

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