Amylopectin starch

Amylopectin (Section 25.15) A polysaccharide present in starch. Amylopectin is a polymer of a(l,4)-linked glucose units, as is amylose (see aniylose). Unlike amylose, amylopectin contains branches of 24-30 glucose units connected to the main chain by an a(l,6) linkage. 

In a current rheological study [296], the galactoxyloglucan from Hymenia courbaril was mixed with starch containing 66% amylose and with waxy corn starch (amylopectin). The gel mixtures showed, under static rheological conditions, an increase in paste viscosity compared to those of the polysaccharides alone. Dynamic rheometry indicated that the interactions resulted in increased thermal stability of the gel formed in comparison to that of the starch alone. 

Hydroxyethyl starch (HES) is a derivative of the highly branched starch, amylopectin, in which the anhydroglucose residues are substituted by hydroxyethyl groups to reduce metabolic degradation by plasma a-amylase. The... 

Branched starches (amylopectin and glycogen) have branches added at this position... 

Equation (17) has been validated via experiments using simple liquids [35, 37], and has been applied to studies on solutions, and gels, as well as solid foods. PGSE has been used in studies on the obstruction and solvation effects related to the macromolecular shape factor for ovalbumin [38], wheat starch amylopectin [39], and for agarose gel [40]. 

The large proportion of short chains (Bl- and A-chains) present in A-type starch amylopectin is located within one cluster, with their non-reducing ends free and unrestricted. These short chains have more freedom to move around and are likely... 

The other component of starch, amylopectin, contains up to 106 glucose units. It is similar to amylose in that the glucose monomers are connected by a-glycosidic bonds between carbons 1 and 4. It differs, however, in that it has branches that occur every 20 to 30 glucose units. These branches are also amylose-type chains that are connected to the main chain by an a-glycosidic bond from carbon 1 of the branch to carbon 6 of the main chain ... 

Both the amylose and amylopectin components of starch form complexes with iodine, but early studies showed that there is no connection between the iodine reaction and the reducibility of starch fractions.63 The complex of amylose is pure blue, whereas the complex of amylopectin is blue-violet.5864 Thus, the varying amylose-to-amylopectin ratio can be one of the factors responsible for the various shades of blue color exhibited by various varieties of starch. Amylopectin takes up less iodine than does amylose. Also the course of complex formation uptake is different, as is evident65 from Fig. 2. 

The second major component of starch, amylopectin, is a branched polysaccharide, containing spine 1,6-a linkages in addition t tj l pi)ding that occurs in amylose, as in Figure 9-37. This branching... 

When starch, amylopectin or glycogen is saccharified by /S-amylase and the maltose is removed, there remains the limit dextrin, called /3-amylase dextrin, Grenzdextrin, a-amylodextrin or in publications from the author s laboratory, simply -dextrin. It gives viscous solutions and is colored blue or violet by iodine. After precipitation with alcohol... 

Fig. 2.—Absorption Spectra of Polysaccharide-Iodine Complexes. (I) Mytiltis edulis glycogen, (II) rabbit liver glycogen, (III) waxy-maize starch (amylopectin). [Solutions contained 0.01% of polysaccharide and 0.02% of iodine in 0.2% of potassium iodide, and were read against an iodine—potassium iodide reference solution.]...

Schematic of range of glass transition data for low moisture cereal foods and their major components (starch, amylopectin, gluten).

Volatile product Starch Amylopectin Amylose D-Glucose... 

Bryce and Greenwood studied the kinetics of formation of the major volatile fraction from potato starch, and its components. They limited their interest to the temperature range from 156 to 337 and to the formation of water, as well as of carbon mon- and di-oxide. The results revealed the following facts. Stability toward pyrolysis within the first 20 minutes of the process falls in the order amylose < starch < amylopectin < cellulose. Autocatalysis is absent, as shown by Puddington. Both carbon mon- and di-oxide are evolved as a consequence of each of two first-order reactions. The initial one is fast, and the second is slow. The reasons are not well understood, but they probably involve some secondary physical effects. The amount of both carbon oxides is a direct function of the quantity of water produced from any polysaccharide, which, furthermore, is independent of the temperature. The activation energy for the production of carbon mon-and di-oxide reaches 161.6 kJ/mol, and is practically independent of the polysaccharide formed. At the limiting rates, the approximate ratios of water carbon dioxide carbon monoxide were found to be 16 4 1 for amylopectin, 13 3 1 for starch, 10 3 1 for amylose, and 16 5 1 for cellulose. 

The other form of starch, amylopectin, is a branched polymer containing both a(l,4) and a(l,6) glycosidic linkages. The 0(1,6) branch points may occur every 20-25 glucose residues and prevent helix formation (Figure 7.32a). The number of glucose units in amylopectin may vary from a few thousand to a million. 

Cooking starch in the presence of amino acids may favour the occurrence of Maillard reactions, lowering the bioavailability of lysine in the diet. 13C CPMAS was used to follow the effect of Maillard reactions on the bioavailability of potato starch.124 A loss of crystallinity was found for the three samples studied starch, amylopectin, and amylose, being more marked for amylose. A similar study on chestnut starch indicated that Maillard reactions do not influence significantly its digestibility.125 NMR was used to characterize some Maillard reaction products extracted from model reactive mixtures such as starch-glucose-lysine 126 and lactose-lysine.127... 

FIGURE 3.9 Three-dimensional representation of starch (amylopectin). 

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