Amylopectin fine structure

Starch functionality in food systems is primarily related to its gelatinization, retrogradation, and pasting properties. The functionality of native starch varies with botanical somce, amylopectin fine structure, and amyloseiamylopectin ratio. 

Table III shows the results of chemical analyses of amylose samples compared, where possible, with values of Mn. These indicate the presence of more than one nonreducing, terminal group in some of the amylose samples. In the case of potato starch, this result is thought to be attributable to the presence of contaminating amylopectin rather than to inherent branching in the molecule.106 Other methods of examining the fine structure of amylose, and the question of branching, will be dealt with later (see p. 381).

Amylo-1 —> 6-glucosidase obtained by Cori and Larner218 from rabbit muscles, and R-enzyme isolated by Hobson, Whelan and Peat219 from potatoes and broad beans, are typical debranching enzymes, which will hydrolyze the 6 — 1-a-D-glucosidic linkage rather than the normal 4 —> 1-a-D linkage. These enzymes will therefore be particularly important in determinations of the fine structure of amylopectin, if they can be sufficiently well purified. 

Figure 6.12 Proposed cluster model of smooth pea amylopectin (a) the mode of interconnection of small structural units to build up dextrin b1. Arrows trace the sub-pieces (included in boxes) of the larger dextrins (b) the fine structure of the dextrins showing how the clusters of short chains (—) are interconnected by long B-chains.261...

Formation of 3-Amylase Limit Dextrins of Amylopectin and Determination of their Fine Structure... 

All chapters/subjects that were also in the previous edition have been updated. Chapters have been added on the biochemistry and molecular biology of starch biosynthesis, structural transitions and related physical properties of starch, and cyclo-dextrins. There are two chapters on the structural features of starch granules that present not only advances in understanding the organization of starch granules, but also advances in understanding the fine structures of amylose and amylopectin, both of which are based on techniques that have been developed since 1984. 

The greatly enlarged chapter on wheat starch presents advances in its production, the differences between large and small granules, the fine structures of wheat starch amylose and amylopectin, genetic and chemical modification of wheat starch, and its functionalities and uses, especially in food products. 

Data on the fine structure of amylopectin from several sources have been obtained through the action of )8-amylase and pullulanase 104, 105, 106). Pullulanase removes specifically the a-D-(l- 6) linkages in amylo-... 

Although, on the basis of chemical studies, it was possible to ascertain the gross structures of the molecules of starch and glycogen, the use of highly purified enzymes has become established as one of the most versatile and definitive methods for the determination of the fine structure of these polysaccharides. The use of these techniques in the examination of the fine structures of glycogen, amylopectin, and amylose will now be discussed. 

Jiang, H., W. Diane, and P. Wu. 2003. Effect of high temperature on fine structure of amylopectin in endosperm by reducing the activity of starch branching enzyme. Photochemistry 63 53-59. 

Interest in the genetic engineering of both plants and micro-organisms for the production of tailor made amylose, amylopectin and/or starches has also been reported. Furthermore, investigations on the enzymatic modification of starch and its major components, for example the introduction of additional branches composed of glucose and/or other monosaccharides and/or uronic acids as well as amino acids or peptides, to produce carbohydrates of possibly comparable functionality to galactomannans, pectin, gum arable, etc., has been initiated. Also studies on the metabolic fate of carbohydrates in food, the biosynthesis of starch, the fine structure of starch from different sources, the effect of electrolytes on the gelatinization of starch and the development of enzymic methods for starch analyses are still active. 

Affinity Chromatography. The interaction of concanavalin A with alpha-D-glucans has been used in the determination of the fine structure of amylopectin and glycogen(88), where correlation between the external chain length of the glucan and the hydrodynamic volume has been established. 

Figure 6.5. Fine structure of amylopectin A, Meyer-Bernfeld tree structure for amylopectin, adapted from ref. [25] B, French/Nikuni cluster structure for amylopectin, from refs. [26,27] with permission from the publisher C, detailed cluster structure for amylopectin, reprinted from ref. [28], with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK and the author.

Since amylopectin acetate produces only brittle films and plastics, its molecules probably have a non-linear structure which may be branched or coiled. A further striking difference between amylose triacetate and amylopectin triacetate is that the former can be obtained in the form of a highly fibrous mass, whereas the latter occurs only as a fine powder. 

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