Amylopectin water insoluble

Figure 17-5. Amylose, cellulose. Amylose consists of a water-soluble portion, a linear polymer of glucose, the amylose and a water-insoluble portion, the amylopectin. The difference between amylose and cellulose is the way in which the glucose units are linked. In amylose, a-linkages are present, whereas in cellulose, p-linkages are present. Because of this difference, amylose is soluble in water and cellulose is not. Chemical modification allows cellulose to become water soluble.

Problem 22.44 Amylopectin, the water insoluble fraction of starch, behaves like amylose, except that more 2,3,4,6-tetra-O-methyl-D-glucose (5%), and an equal amount of 2.3-di-O-methyl-D-glucose, is formed. Deduce the structure of amylopectin. 

Cellulose, a fibrous, tough, water-insoluble substance, is found in the cell walls of plants, particularly in stalks, stems, trunks, and all the woody portions of the plant body. Cellulose constitutes much of the mass of wood, and cotton is almost pure cellulose. Like amylose and the main chains of amylopectin and glycogen, the cellulose molecule is a linear, unbranched homopolysaccharide, consisting of 10,000 to 15,000 D-glucose units. But there is a very important difference in cellulose the glucose residues have the /3 configuration (Fig. 7-16),... 

Amylopectin a component of starch (the other is amylose). A. is a branched, water-insoluble polysaccharide (A/, 500,000-1,000,000) consisting of a main chain of a-l,4-linked D-glucose units with side chains (15-25 D-glucose units) attached a-1,6 to every 8th or 9th glucose. A. forms violet to red-violet inclusion compounds with iodine. It swells in water, and upon heating it forms a paste. 

The other main form of plant starch is amylopectin, which has a molar mass as high as 150,000,000 g/mol (Fig. 22.13). It has the same a(l 4) bonds as amylose, but it also has branches designated o (l 6). As a result of its high molar mass and its branches, amylopectin is insoluble in water. 

Starch is another polymer of glucose, like cellulose. But you know that starch is quite different from cellulose. Plant starch typically consists of two components water-soluble amylose and water-insoluble amylopectin. Amylose is a linear polymer of glucose, but its connection is different from that in cellulose. The structure of amylopectin is different from that of amylose. We discuss these issues later. 

In its native state, starch is semi-crystalline (about 20-45%) and water insoluble. Native starch granules typically have dimensions ranging from 0.5 to 175 pm and appear in a variety of shapes. It is composed of linear (amylose) and branched (amylopectin) polymers of ot-D-glucose. Amylose has a molecular mass of about 10 -10 g moU while amylopectin has a molecular mass in the range 10 -10 g moU Starch rich in amylose is usually preferred for conversion to TPS as the linearity of amylose improves the processability of starch even though it is present as a minor component (between 20 and 30wt%). The ratio of amylose to amylopectin depends on the source and age of the starch, and can also be influenced by the extraction process. ... 

Following the method developed by Davis and Flitsch [90] using a mixture of sodium hypochlorite, sodium bromide and 2,2,6,6-tetramethyl-l-piperidine oxoammonium radical, the TEMPO-NaBr-NaClO system was applied to a wealth of products including many polysaccharides. This method was first proposed for water-soluble polysaccharides [3, 5-8], namely starch, inulin, amylodextrin, pullulan, alternan, amylopectin, chitosan, galactomannan, and later extended to water-insoluble products [7-12], such as cellulose, amylose, and chitin. 

Starch consists of two main components amylose (insoluble in cold water) and amylopectin (soluble in cold water). Amylose, which accounts for about 20 per cent by weight of starch, has an average molecular weight of over 10. It is a polymer of glucopyranose units linked together through a l,4 -linkages in a linear chain. Hydrolysis of amylose produces maltose. Amylose and iodine form a colour complex, which is blue/black. This is the colour reaction of iodine in starch, a confirmatory test for the presence of starch. 

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