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Light-Scattering Molecular Weights and Intrinsic Viscosities of Processed Waxy Maize Starches in 90% Dimethyl Sulfoxide and H₂O

¹Bioactive Agents Research, Biomaterials Processing Research, Plant Polymer Research, and Biomaterials Processing Research, respectively, United States Department of Agriculture, Agriculture Research Service, Midwest Area, National Center for Agricultural Utilization Research, 1815 N. University, Peoria, IL 61604. Mention of trademark or proprietary products does not constitute a guarantee or warranty by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. ²Corresponding author. E-mail: willetjl@mail.ncaur.usda.gov

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 [η] and multiangle light-scattering measurements were made in 90% DMSO-H₂O. A Mark-Houwink relation, [η] = (0.28–1.2) M_w^{0.29 ± 0.04}, was obtained over a molecular weight range of ≈30–700 million. However, there was a large amount of scatter in the data when [η] were >140 mL/g. The power law relationship R_g ∝ 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.