Amylopectin separation

For the irradiation of amylose it has been shown that the solvent may stabilize the irradiated matrix. Thus the scission of amylose in dimethyl sulfoxide is almost 15 times lower than that in water.92 Irradiation of the solution simultaneously containing amylose and amylopectin separated resulted in their grafting.93 Thus the results of irradiation depend on whether starch is radiolyzed in the solid, paste,... 

Amylopectin of potato starch and probably amylopectin of other tuber starches occurs as a natural ester of phosphoric acid. Potato amylopectin" contains approximately 0.07-0.09% phosphorus, " or one phosphate group for every 212 to 273 anhydroglucose units. The phosphate appears to be attached mainly to the primary alcohol group since, on hydrolysis, potato amylopectin (separated by electrodialysis)... 

Amylopectin differs from amylose in that its retr< adation from solution is slow. The setting of starch gels (cornstarch puddings) and the staling of bread are, however, due to amylopectin separation. With iodine amylopectin gives a purple to red color, and it may be distingui ed from amylose in a potentiometric titration with iodine, since it does not form a complex. 

FIGURE 16.7 Native starch ( ) and fractions of native starch differing in their branching characteristics (nb/lcb amylose -type fraction scb amylopectin -t/pe fraction ) separated on semipreparative... 

Starches can be separated into two major components, amylose and amylopectin, which exist in different proportions in various plants. Amylose, which is a straight-chain compound and is abundant in potato starch, gives a blue colour with iodine and the chain assumes a spiral form. Amylopectin, which has a branched-chain structure, forms a red-purple product, probably by adsorption. 

Perhaps the most important advance in the chemistry of starch was the realization of the apparent inhomogeneity of the material, followed by its fractionation into simpler components—first carried out quantitatively by Schoch1 in 1941. Starches can, in general, be separated into at least two chemically distinguishable entities amylose, a mixture of essentially unbranched chains, and amylopectin, a mixture of highly branched chains.2... 

The labile nature of the components necessitates that, for fundamental investigations, the starch should preferably be extracted from its botanical source, in the laboratory, under the mildest possible conditions.26 Industrial samples of unknown origin and treatment should not be used. The characterization of the starch would appear to entail (1) dissolution of the granule without degradation, (2) fractionation without degradation, (3) complete analysis of the finer details of structure of the separated components (including the possibilities of intermediate structures between the extremes of amylose and amylopectin), and (4) the estimation of the size, shape, and molecular-weight distribution of these fractions. 

Although it has been found that the separated amylose component can be readily orientated to yield fiber patterns, amylopectin usually gives poor or amorphous patterns. In the granule, however, amylopectin does exhibit crystallinity, since waxy maize starch gives a diffraction pattern and other waxy starches behave similarly.193 -195 (This suggests that the branch points in the amylopectin molecule may be in the amorphous part of the granule.)... 

Starch is the major energy store of plants chemically it is a polymer of glucose and occurs in two separate forms, amylose and amylopectin. The ratio of the two types depends on the plant that the starch has come from typically starch is 20 30% amylose and 70-80% amylopectin but there are amylomaizes with more than 50% amylose while waxy maize produces almost pure amylopectin with less than 3% amylose. 

The variation between the starch from different plants is considerable. The percentage of amylose varies from 27% in maize starch through 22% in potato starch to 17% in tapioca starch. The waxy maizes are unusual in that they are almost pure amylopectin. This is extremely convenient because it avoids the need to separate amylopectin from amylose chemically. 

A second reason for the turn-over in the osmotic modulus may arise from a decrease in A2 until it becomes zero or even negative. This would be the classical situation for a phase separation. The reason why in a good solvent such a phase separation should occur has not yet been elucidated and remains to be answered by a fundamental theory. In one case the reason seems to be clear. This is that of starches where the branched amylopectin coexists with a certain fraction of the linear amylose. Amylose is well known to form no stable solution in water. In its amorphous stage it can be brought into solution, but it then quickly undergoes a liquid-solid transition. Thus in starches the amylose content makes the amylopectin solution unstable and finally causes gelation that actually is a kinetically inhibited phase transition [166]. Because of the not yet fully clarified situation this turn-over will be not discussed any further. 

The dependence of the mobilities of amylopectin and amylose on iodine concentration in the background electrolyte and applied temperature was studied by Brewster et al. (111). The method was used for the separation and identification of different plant starches, but no binding constants were calculated. 

It is generally believed that the physical state of the amylose component is amorphous and therefore it is found in the amorphous parts of the granules. It is, however, not separated from the amylopectin component. By chemically cross-linking the polymers, it was shown that amylose... 

The crystallinity of starch granules is disrupted during derivatization (Saroja et al., 2000), and this leads to a greater degree of separation between the outer branches of adjacent amylopectin... 

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. 

A further factor that causes the non-homogeneity of nitrostarch is the presence of the two components, amylose and amylopectin in starch. It has been demonstrated by nitrating each of these starch components separately that the nitration products differ from one another. Berl and Kunze [37] detected that amylopectin yields a product of a considerably higher viscosity than that resulting from the nitration of amylose. This effect may be attributable to the higher molecular weight of amylopectin. 

There have been several examinations of the structure of Nageli dextrin,405407 which is prepared by the prolonged action of acid on granular starch. In one study,405 there was separated from waxy maize a branched fraction that was resistant to pullulanase action. As this fraction contained some molecules having two branch points that were in close proximity, it was considered that this may have hindered hydrolysis, and that it could be of relevance to studies on the structure of the original amylopectin. 

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