Contribution of amylose and amylopectin to the light scattering behaviour of starches in aqueous solution

Investigations based on static and dynamic light-scattering studies were conducted to assess the influence of amylose content (0.0-65.8%) and microwave dispersion treatment (MDT) on the macromolecular features of starches, including fractal behaviour. Values for apparent average molar mass ((M) over bar(w)), gyration radius ((R) over bar(G)) and hydrodynamic radius ((R) over bar(H)) were obtained using common extrapolation procedures to the zero scattering vector. The general trend showed a decrease in these values when amylose level or the intensity of MDT was increased. However, unexpected results were obtained. mainly for the starch with the highest amylose content and for long MDT times. The high q (R) over bar(G)-range [where q is the scattering vector; q = (4 pi n/lambda)sin(theta/2)] allowed the internal behaviour of starch samples to be studied as well. Kratky plots, fractal dimensions, and relaxation rate dependence on q revealed significant differences in internal structures and the influence of amylose content. At low amylose contents (0.0-28.5%), light-scattering behaviour was dominated by the amylopectin contribution, in agreement with Galinski and Burchard (Macromolecules 1995;28:2363), whereas at high amylose contents (52.5-65.8%), light-scattering behaviour was influenced by amylose despite the high dimensions of amylopectin. (C) 1999 Elsevier Science Ltd. All rights reserved.