Amylose isolation

Amyloses of different origins and molecular weights have been extensively studied.151 Results indicate that cereal amyloses are smaller than other amyloses. Amyloses isolated from high-amylose maize starches display substantially smaller molecular weights (average DP 690-740 and chain lengths 215-255).161 There is about an equal... 

Successful methods entail precipitation of the amylose from solution as an insoluble complex, which is removed by high-speed centrifuging the amylopectin is isolated from the supernatant liquor by precipitation with alcohol or, more satisfactorily, by freeze-drying. (Precipitation with alcohol does not always appear to be quantitative, and the physical form of the product obtained by freeze-drying is more satisfactory for subsequent dissolution and esterification.) The amylose can then be further purified by reprecipitation with the same or, preferably, a different complexing agent. 

It is often important to examine the solids which can be isolated from the supernatant liquors obtained during a fractionation, as it would appear that subfractionation of amylose can occur.28... 

Table I shows the results of periodate oxidation and methylation applied to amylopectins from various sources. If the percentage of amylose in a whole starch is known, the length of unit chain of the amylopectin component can be calculated from the results of periodate oxidation of the whole starch (see Table II). The length of unit chain appears to depend on the botanical species, but not the variety, from which the starch wras isolated. In the case of tapioca and corn amylopectins, sub-fractionation of these by precipitation with methanol, followed by periodate oxidation, showed the sub-fractions had the same degree of branching as the original amylopectins.71 The action of periodate on whole starches and amylopectins is now so well established and accurate, that it may well completely supersede the methylation technique for pure starches, in view of its many advantages.

The composition of branched building blocks in the isolated clusters of the amylose-free potato starch, was analyzed by treating the clusters with excess a-amylase (Bertoft, 2007b). Under such conditions, the enzyme is forced to continue the attack at internal chains shorter than 9 residues inside the clusters. As a resultthe building blocks, which practically resist further attack... 

Structural analysis of isolated amylose and amylopectin components has been carried out by standard methods based on methylation, periodate oxidation, and partial acid hydrolysis studies. Methylation and periodate oxidation studies established the linkage types and frequency of... 

The nonbonded energy (van der Waals) is computed for isolated helical amylose chains as a function of the dihedral angles (, relative orientations of the glucose residues in the polysaccharide chain. In conformity with x-ray data, different helical conformations ere proposed for different crystalline modifications of amylose. 

Probably the most important carbohydrate polymer in food, certainly from a nutritional standpoint, is starch, and Chapter E2 presents three units that can be used for starch isolation and characterization. UNITE2.1 condenses many different starch isolation methods into one scheme for starch isolation from virtually any plant source. In this protocol, the author notes the care that must be taken to prevent starch degradation during isolation. unite2.2 presents a simple enzymatic analysis method that can be used for estimation of starch in food. Finally, unit E2.3 describes a colorimetric method to determine starch amylose content. Again, different combinations of the units in this chapter can be used to characterize starch from any source. 

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