Amylopectin constitution

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),... 

Starch granules are composed of two different polysaccharides, amylopectin and amylose the former constitutes about 80 % of the most common starches. Separation of the two components can be achieved by selective precipitation involving the formation of an insoluble complex of amylose with polar organic substances. 

On the basis of researches devoted to the products of paitial or total hydrolytic breakdown of methylated starch, the chain of a-D-anhydroglucose is thought to constitute the main element of the amylose and amylopectin molecules. These units are combined as in maltose, i.e. by means of a-glucosidic linkages formed between the carbon atoms 1 and 4 ... 

Figure 20-3 Proposed structure of a molecule of amylopec-tin in a starch granule. The highly branched molecule lies within 9 nm thick layers, about 2 / 3 of which contains parallel double helices of the kind shown in Fig. 4-8 in a semicrystalline array. The branches are concentrated in the amorphous region.113 114 121 Some starch granules contain no amylose, hut it may constitute up to 30% by weight of the starch. It may he found in part in the amorphous bands and in part intertwined with the amylopectin.122...

Starches are the major carbohydrates of such foods as com, wheat, and rice (Table 2,5). Potatoes and legumes are also rich in starches. Most starches are a mixture of amylose and amylopectin, as shown in Table 2.6. in general, amylose constitutes about one-third of the starch in various foods the remainder is amy-lopectin. Of the dry matter of the plants listed in Table 2.4, 70-90% consists of stanch. These plants are called starchy foods. Take special note of the general constituents of the cassava root- (Tapioca is made from cassava.) This food has the loVilest protein/carbohydrate ratio of any of the foods listed in Table 2.5, about 1/25 for cassava compared with about 1/5 for wheat. 

Amylose derivative. R or R = H or CHjCHjOH. Amylopectin derivative. Differs from the amylose deriv in that the sequence is frequently interrupted by a unit in which R is the residue of an additional O-hydroxyethylated a-D-glucopyranosy] moiety that constitutes the first unit in a branch or sub-branch of the polymer. 

Chemically, starch is a polymer of anhydroglu-cose, (CgHjpOj)jj. It is constituted of 17-27 wt% of amylose with a-1,4-linkages between the units, and amylopectin with a-1,6-linkages. Amylose is a linear polymer, with (MW = 200 to 2,000 kg/mol), while amylopectin is a branched one (MW = 100,000 to 400,000 kg/mol). In nature,... 

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