Starch separation from amylopectin

On treating with hot water, starch is separated into the soluble amylose and the insoluble amylopectin. Alternatively, the amylose can also be separated from amylopectin by precipitation from aqueous solution with butanol or by dissolution in liquid ammonia. Generally, starches contain... 

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. 

Montgomery, E. M., and Senti, F. R. (1958). Separation of amylose from amylopectin of starch by an extraction-sedimentation procedure./. Polym. Sci. 28 1-9. 

It should be noted that the different structures of amylose and amylopectin confer distinctive properties to these polysaccharides (Table II). The linear nature of amylose is responsible for its ability to form complexes with fatty acids, low-molecular-weight alcohols, and iodine these complexes are called clathrates or helical inclusion compounds. This property is the basis for the separation of amylose from amylopectin when starch is solubilized with alkali or with dimethylsulfoxide, amylose can be precipitated by adding 1-butanol and amylopectin remains in solution. 

From Fig. 3, it may be seen that lowering of the temperature to 60-70 will cause separation of amylopectin. In general, this phase separation takes the same route as that for the amylose (except for the peculiar, morphological phenomena of the latter). As crystallization is much slower for the branched fraction of starch, the critical temperature of phase separation is sufficiently high to permit the existence of a coherent, liquid phase for short periods of time. The fact that freshly obtained amylopectin precipitate is soluble in cold water, whereas, after several hours, it is completely insoluble in cold water can only be interpreted as being the result of crystallization. In accordance with this conclusion, it is to be noted that this phenomenon is perfectly reversible. 

Although separation of amylose from amylopectin is the main purpose of the process described, it has been observed that subfractionation of at least one of the two components of starch (namely, amylose) likewise occurs. In this connection, it is to be noted here that the experimental results strongly indicate that fractionation of amylose into its different molecular-weight species is remarkably efficient in salt solutions. In view of the great disparity in solvent power between the precipitant and the solvent in the case of aqueous salt solutions, this conclusion seems to confirm some predictions of Flory s. "... 

The separation and purification of starch granules from plant extracts (see O Sect. 2 in O Chap. 6.2) and the fractionation of amylose and amylopectin is given in O Sect. 5 in O Chap. 6.2. The separation of cellulose and hemicelluloses from plant materials and from each other is given inO Sect. 3.2 inO Chap. 6.3. 

The /3-amylases in the absence of the a-amylases are incapable of degrading whole starches completely. The hydrolysis proceeds rapidly until about 50 to 55 % of the theoretical amount of maltose is produced and then very slowly until a limit of about 61 to 68% is reached (101), The solution is still viscous and the residue, called a /3-amylase limit dextrin, is unfer-mentable. The limit dextrin arises from the inability of /3-amylase to act beyond a branch point in the randomly branched amylopectin molecule and may be envisaged as a pruned amylopectin structure. In the case of potato starch, the /3-limit dextrin includes all the associated phosphate. The limit dextrin contains one end group for every 10 to 12 D-glucose residues (102), in contrast to one in every 25 or 30 residues for the original amylopectin. The initial attack of /3-amylase on amylopectin is about 20 times as fast as on amylose (103), Maltose in amounts of 53 to 62 % of the theoretical have been reported from the action of /3-amylases on amylopec-tins separated from various starches (104). When the /3-limit dextrin is cleaved by acid hydrolysis or by the action of a-amylase, the structure is opened and new chain ends are made available which can be further acted upon by i3-amylase. 

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. 

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. 

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