LIGHT-SCATTERING MOLECULAR-WEIGHTS AND INTRINSIC VISCOSITIES OF PROCESSED WAXY MAIZE STARCHES IN 90-PERCENT DIMETHYL-SULFOXIDE AND H2O

Waxy maize starch was treated by a variety of gentle and severe method s: direct dispersion-solubilization into 90% dimethyl sulfoxide (DMSO) and H2O solvent, extrusion followed by dispersion-solubilization of t he ground exudate into solvent, or jet-cooking or stirred autoclaving of an aqueous starch slurry followed by transfer into solvent. Intrins ic 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 approxi mate to 30-700 million. However, there was a large amount of scatter i n the data when [eta] were >140 mL/g. The power law relationship R-g p roportional 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 ran ge of M-w distributions, the amylopectin existed in solution as relati vely compact molecules or aggregates and that in the higher molecular weight region, the size and possibly the shape of the ''dissolved'' am ylopectin was highly sensitive to the method of dispersal and treatmen t.