Light-scattering molecular weights and intrinsic viscosities of processed waxy maize starches in 90% dimethyl sulfoxide and H2O

Waxy maize starch was treated by a variety of gentle and severe methods: direct dispersion-solubilization into 90% dimethyl sulfoxide (DMSO) and H2O solvent, extrusion followed by dispersion-solubilization of the ground exudate into solvent, or jet-cooking or stirred autoclaving of an aqueous starch slurry followed by transfer into solvent. Intrinsic viscosities [eta] and multiangle light-scattering measurements were made in 90% DMSO-H2O. A Mark-Houwink relation, [eta] = (0.28-1.2) M-w(0.29 +/- 0.04), was obtained over a molecular weight range of approximate to 30-700 million. However, there was a large amount of scatter in the data when [eta] were >140 mL/g. The power law relationship R-g proportional to M-w(0.41 +/- 0.04) was noted between radii of gyration and molecular weights. We infer from our data that over the entire range of M-w distributions, the amylopectin existed in solution as relatively compact molecules or aggregates and that in the higher molecular weight region, the size and possibly the shape of the ''dissolved'' amylopectin was highly sensitive to the method of dispersal and treatment.