Laser light scattering of high amylose and high amylopectin materials, stability in water after microwave dispersion

Light scattering techniques were used for structural characterization of starches with diverse amylose and amylopectin level, dissolved in water by microwave heating in a high pressure vessel and stored during different times. In general, apparent molar mass ((M) over bar(w)), gyration radius ((R) over bar(G)) and hydrodynamic radius ((R) over bar(H)) values decreased when storage time increased. This emphasised the depolymerization of the samples during the storage time. The fractal dimension obtained from the (R) over bar(G)-(M) over bar(w) relationship showed that the samples presented, in general, a globular structure, with a higher level of branching when amylopectin level in the sample increased. The particle scattering factors and Kratky plots, well suited for studying the internal structure of a macromolecule, showed a depolymerization when storage time increased. The nu(RH) values for Eurylon 5 (0.56) and Eurylon 7 (0.58) starches were close to the values reported for linear chains. For amylopectin (0.09) and normal corn starch (0.10) the nu(RH) values were lower; these values would define a highly branched structure. The relaxation rate distribution of the samples showed that there are changes in the internal structure when storage time increases, and that these changes depend on amylose and amylopectin level present in the sample. The rho values for the samples analyzed were between 0.88 and 1.3; these values are characteristic of branched structures. (C) 1998 Elsevier Science Ltd. All rights reserved.