Conformational Contributions of Amylose and Amylopectin to the Structural Properties of Starches from Various Sources

Abstract

Six starches of different amylose content were studied by static light scattering from very dilute aqueous solutions at 20°C. Reproducible results were obtained after submitting the solutions to a controlled autoclaving step where the solutions were heated up to 135‐155°C. Amylose rich starches exhibited significantly different angular dependences from those with low amylose content. The high experimental accuracy of the angular dependences allowed separate determination of the molar masses Mw and radii of gyration Rg for both components in the mixture. Molar masses of 60‐10 6 to 110‐ 10 6 and radii around 220nm were found for the amylopectins from the various starches. Unexpectedly high molar masses between 450‐10 3 and 2.5‐10 6 were found for the amylose components but only low radii of gyration. Comparison with synthetic amyloses indicate strong intra and intermolecular aggregation in the form of laterally (side‐by‐side) aligned chains which could contain up to 35 amylose chains. The possibility of a quantitative determination of the degree of branching via the shrinking factor g (=Rg 2 Ap/Rg 2 Am I at the same molar mass) is discussed at some length.