Problems in the physical chemistry of polysaccharides: the structure and solution behaviour of potato amylose

Physical techniques, including rotational viscometry and several ultracentrifugal methods not previously used in these laboratories have been detailed.The viscometric behaviour of the amylose component of potato starch dissolved in aqueous alkaline solution was found to depend on pH and counter-ion concentration. Maximum [π]- values occur- red at a pH of approximately 13 and these were reduced, on the addition of salt, to values below those found in neutral solution. In these solvents, where [π]-values were minimal, the solution behaviour resembled ideal θ-conditions. Changes in [π] were interpreted as changes in the conformation of the amylose molecule due to the ionisation of hydroxyl groups. These effects were confirmed for amylose fractions of varying molecular-weight.The absolute viscosity of solutions of amylose in 0.33M KCl, 0.15M KOH and 1M KOH was found to be dependent on the average shear rate G, between G = 0 -1200 sec⁻¹. Limiting viscosity numbers, [[π], were however, independent of shear rate even for the largest molecular weight samples of amylose.The subfractionation of both total-amylose and linear-amylose has been studied in detail, and the fractional precipitation of amylose from a dimethyl-sulphoxide solution with acetone was found the most efficient method. In the subfractionation of total - amylose, a heterogeneity was evident in some subfractions, and its presence was related to the ß- amylolysis limit. It was shown that this heterogeneity was natural to the polysaccharide, and probably represented branched material.From a study of the properties of subfractions of linear amylose, the polysaccharide was found to behave as a random coil in 0.50M KCl/10⁻²M KOH (an aqueous 9- solvent), 0.15M KCl, and 0.15M KOH. The amylose molecule was in a more expanded form in the latter two solvents. Moreover, there was some evidence for association in neutral aqueous solutions of natural amylose.The concentration dependence of sedimentation coefficient was negligible for amylose dissolved in the above θ-solvent, but increased with solvent power in accord with theory. In addition, the apparent sedimentation coefficient was dependent on forcefield.By fractionating total potato starch, the presence of polysaccharide-material intermediate in structure between linear amylose and highly ramified amylopectin was confirmed. These results suggest that a continuous range in molecular structure may be present in the starch granule. Intermediate material was composed of branched polysaccharides similar to both amylose and amylopectin