Amylopectin soluble

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. 

Starch can be split into amylose and amylopectin by a commercial process based on selective solubilities. Amylose is used for making edible films, and amylopectin for textile sizing and finishing, and as a thickener in foods. 

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.

The data19 summarized in Figure 1 show that the extent of the hydrolysis of soluble potato starch by barley beta amylase reaches a limit which is independent of the concentration of the amylase. The data are typical of the action of beta amylases on unfractionated starches, when the hydrolyses are carried out at or near pH 4.5.1 3 6 19 20 Under these conditions, the hydrolysis of unfractionated starches usually ceases when 60 to 64% of the maltose theoretically obtainable from the substrate has been formed. The exact value of the limit obviously will depend upon the concentration of amylopectin in the starch and upon its structure. 

Table I lists physical data for a number of the carbamate and ester derivatives of cellulose, chitin, amylose, amylopectin, and dextran synthesized as described in the Experimental Section. The solubility of the polysaccharide starting materials as well as that of the produced derivatives allows for macromolecular characterization through techniques including UV, NMR, IR, high pressure liquid chromatography, etc.

In comparison with a pullulanase, the purified amylopullulanase displayed 3-fold higher specificity towards soluble starch and amylopectin and 7-fold higher specificity towards glycogen (12). The amylopullulanase hydrolyzed various high molecular weight starch substrates (Table II). Even the mammalian glycogen which... 

Solutions of 1% (w/v) puUulan, amylose, amylopectin, mammalian glycogen, oyster glycogen and soluble starch (pH 6.0) were incubated at 60 C with purified enzyme (0.05 U/ml). Samples were withdrawn after 216 hrs and heated at lOO C for 15 min for enzyme inactivation. The reaction products were analyzed by HPLC for sugars. (12). (Reprinted with permissicm from Ref. 13. Copyright 1990 Academic Press, Inc.)... 

Amylopectin Amylopectin is similar to amylose except that the glucose chain has branches. These branches involve linkages at the -CH2OH position ( 6), which makes them a 1 —> 6 linkages. Amylopectin is water-soluble it also interacts with iodine to form a reddish-purple complex. Typically, amylopectin is ten times the size of an amylose molecule. Digestion requires (3-amylase (1 4 linkages) and a second... 

Amylose, although water soluble, gives an unstable solution which irreversibly precipitates. It is mainly responsible for the deep blue coloration given by starch and iodine. Solutions of amylopectin are relatively stable. The iodine-binding capacity, on the other hand, is very low. A small amount of covalently bound phosphate normally appears with starch but its exact location within the molecule is not known. 

The solubility of the amylose nitration product in ether-alcohol was reported (Ashford, Cook and Hibbert [39]) to be lower, e.g. 20%, than that of the nitration product of amylopectin, which is 86-87%. Such behaviour is explicable in terms... 

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